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ANESTHESIA BASICS:
THE ROLE OF THE
NURSE ANESTHETIST
Jassin M. Jouria, MD
Dr. Jassin M. Jouria is a medical doctor,
professor of academic medicine, and medical
author. He graduated from Ross University
School of Medicine and has completed his
clinical clerkship training in various teaching hospitals throughout New York,
including King’s County Hospital Center and Brookdale Medical Center, among
others. Dr. Jouria has passed all USMLE medical board exams, and has served as a
test prep tutor and instructor for Kaplan. He has developed several medical courses
and curricula for a variety of educational institutions. Dr. Jouria has also served on
multiple levels in the academic field including faculty member and Department Chair.
Dr. Jouria continues to serves as a Subject Matter Expert for several continuing
education organizations covering multiple basic medical sciences. He has also
developed several continuing medical education courses covering various topics in
clinical medicine. Recently, Dr. Jouria has been contracted by the University of
Miami/Jackson Memorial Hospital’s Department of Surgery to develop an e-module
training series for trauma patient management. Dr. Jouria is currently authoring an
academic textbook on Human Anatomy & Physiology.
Abstract
The rapid growth of nurse anesthetists within surgical and other health
settings has helped to improve available, cost-effective services for
patients. Nurse anesthetists have a vital role in the management of
the perioperative patient as well as in the provision of clinical support
services outside the operating suite. As experienced anesthesia
clinicians, they are able to assist in the education and training of new
nursing and medical staff in the provision of safe and appropriate care
during varied anesthesia procedures, including pre- and postanesthesia care. With such a wide array of responsibilities, nurse
anesthetists must possess a broad field of clinical knowledge.
Policy Statement
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This activity has been planned and implemented in accordance with
the policies of NurseCe4Less.com and the continuing nursing education
requirements of the American Nurses Credentialing Center's
Commission on Accreditation for registered nurses. It is the policy of
NurseCe4Less.com to ensure objectivity, transparency, and best
practice in clinical education for all continuing nursing education (CNE)
activities.
Continuing Education Credit Designation
This educational activity is credited for 4.5 hours. Nurses may only
claim credit commensurate with the credit awarded for completion of
this course activity. Pharmacology content is 1 hour.
Statement of Learning Need
Nurse anesthetists need to know their role and responsibilities in the
management of the patient receiving varied types of anesthesia.
Importantly, as members of the anesthesia team, they are actively
involved in the patient’s pre- and post-operative care relating to the
preparation and planning, administration and recovery phase of
anesthesia that require them to continuously update their own
knowledge as practicing clinicians and as clinical leaders and educators
of anesthesia practice in multiple settings, including Intensive Care
Units, Palliative Care Units, and a wide array of inpatient and
outpatient surgical services.
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Course Purpose
To provide advanced learning for clinicians interested in the role and
practice of the nurse anesthetist.
Target Audience
Advanced Practice Registered Nurses and Registered Nurses
(Interdisciplinary Health Team Members, including Vocational Nurses
and Medical Assistants may obtain a Certificate of Completion)
Course Author & Planning Team Conflict of Interest Disclosures
Jassin M. Jouria, MD, William S. Cook, PhD, Douglas Lawrence, MA,
Susan DePasquale, MSN, FPMHNP-BC – all have no disclosures
Acknowledgement of Commercial Support
There is no commercial support for this course.
Please take time to complete a self-assessment of knowledge,
on page 4, sample questions before reading the article.
Opportunity to complete a self-assessment of knowledge
learned will be provided at the end of the course.
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1. _____________ is used to anesthetize an area of the body.
a.
b.
c.
d.
Local anesthesia
General anesthesia
Sedation
Regional anesthesia
2. True or False: The term “asleep” is used when anesthesia
clinicians speak of a patient who is anesthetized because
general anesthesia is similar to sleep in physiological terms.
a. True
b. False
3. The triad model of anesthesia means that _______________
needed to produce all three of the intended effects of
anesthesia: narcosis, analgesia, and muscle relaxation.
a.
b.
c.
d.
sedation is
an anesthesia care team is
multiple agents are
only one agent is
4. Which of the following is characteristic of electrical brain
activity in an anesthetized subject but not an individual who
is sleeping?
a.
b.
c.
d.
Rapid eye movement (REM) sleep
Non-REM sleep
Burst suppression
Aniso-electric periods
5. Pain signals turn into perceived pain at the moment the
sensory pain signals arrive at the
a.
b.
c.
d.
thalamus.
the cortex.
nociceptors.
peripheral nerves to the spinal cord.
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Introduction
The anesthesia care team works in collaboration with all members of
the surgical team to provide a plan that is tailored to each individual
patient in terms of intraoperative life support, sedation, pain control,
and postoperative management, to assure an uneventful recovery
from a surgical or other emergency procedure. Outside of the
operating room, medical and nursing anesthetists are involved with
emergency units that provide monitoring, treatment, and support
during diagnostic investigations. They often intervene in intensive care
units, radiology units, acute pain units, and outside the hospital
setting, such as providing care for terminal (i.e., cancer) and
psychiatric (i.e., electroconvulsive therapy) patients. In the United
States, the amount of autonomy that nurse anesthetists have is
variable. Currently, certified registered nurse anesthetists (CRNAs)
may practice without physician supervision in 17 states of the United
States.3
Anesthesia Overview And General Concepts
Due to development of the state of the art surgical and exploratory
tools in general surgery and the sharp rise of subspecialties in Ear,
Nose and Throat (ENT), Ophthalmology, Plastic surgery and
Cosmetics, among other surgical procedures, anesthesia is becoming
the largest hospital medical specialty in many countries. It is
estimated that 234 million surgical procedures are performed annually
that necessitate the use of anesthesia.1 The proportion of nonoperating room anesthesia (NORA) cases increased from 28.3% in
2010 to 35.9% in 2014. There is also a trend of increasing the volume
of NORA care in the United States.2
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Anesthesia involves medication given to relieve pain and sensation
during a medical procedure such as during surgery. Sedation is used to
make a patient calm or sleepy and sedation may also be used as part
of the anesthesia process. In regional anesthesia, the anesthesiologist
makes an injection near a cluster of nerves to numb the area of the
body that requires surgery.
There are three types of anesthesia to consider: 1) local anesthesia
performed typically at the site of the surgical incision, 2) regional
anesthesia used to anesthetize an area of the body (used alone or in
combination with general anesthesia), and 3) general anesthesia
where the patient is made completely unresponsive to pain, in which
case the patient needs assisted ventilation and close monitoring of his
or her physiological status.
Sedation is another important skill area of anesthesia medical and
nursing staff. Often sedation is used in combination with local
anesthesia in light procedures involving the skin or subcutaneous
tissues, minor biopsies, and surgeries of peripheral parts of the body
that can be easily anesthetized with regional injections.
There are several levels of sedation. A mild dose allows the patient to
stay awake or in a drowsy state but easily arousable, such as when
the patient hears his or her name called. As sedation deepens with
increasing doses, the anesthetist may need to maintain the airway
open with support and assist the ventilation of the patient. In its
deepest level, sedation becomes general anesthesia called total
intravenous anesthesia (TIVA), and for this reason should be included
in a discussion of anesthesia types.1,4
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General Anesthesia and the Triad Model
Although the term asleep is used when anesthesia clinicians speak of a
patient who is anesthetized, general anesthesia is very different from
sleep in physiological terms. So, what is general anesthesia? First,
general anesthesia is a term that refers to a state of unconsciousness
deliberately produced by the action of drugs on a patient. This state is
reversible in essence. At its infancy, anesthesia was introduced with
the goal of eliminating pain and was usually provided by a single agent
of ether or chloroform.
In 1926, John Lundy introduced the term “balanced anesthesia” to
describe the use of multiple sedating agents as a premedication
together with general anesthesia to improve results. Later, in the
1950s Gordon Jackson Rees and Cecil Gray proposed a triad of
anesthesia consisting of narcosis (unconsciousness), analgesia, and
muscle relaxation; all represented in a triangular diagram. The triad
model means that one agent is no longer found sufficient to produce
narcosis, analgesia, and muscle relaxation. The triad model is still
taught and used with some refinement.1,4
Anesthesia Is Not ‘Asleep’
An understanding of why anesthesia is not the same as being asleep
may be achieved through observing the electrical activity of the brain
by means of electroencephalography (EEG). Using EEG analysis, sleep
is characterized as two phases. One of these phases is rapid eye
movement (REM) sleep during which vivid dreams occur and REM
sleep accounts for 10% to 20% of sleep time. The other is non-REM
sleep. These two types of sleep form a pattern that lasts about 90
minutes, which is a sleep cycle.4
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Intense electrical activity occurs during the sleep cycle, especially
during the REM phase, which resembles the EEG activity of awake
subjects. In contrast to what happens in wakefulness and sleep, in
anesthetized subjects, the frequency of the brain waves slows and
their overall amplitude diminishes. During general anesthesia the
patient may even experience short periods of silencing called burst
suppression. Therefore, EEG recordings provide evidence that
anesthesia is distinct from sleep.
Analgesia During Anesthesia
The aim of analgesia is to abolish pain sensation experienced by the
patient during surgery and in the perioperative phase as well. The
American Society of Regional Anesthesia and Pain Medicine (ASRA)
define pain as “an unpleasant stimulus, which evokes an unpleasant
reaction in the recipient.”4 This definition incorporates both the
subjective and objective components of pain; the perception of the
individual and the objective measurable effects elicited by the
stimulus.
Briefly summarized, the neurophysiology of pain has been shown to
comprise the following steps. First, the detection of the painful
stimulus (nociception) due to the presence of nociceptors located in
the skin and other organs, which upon their stimulation will produce
electrical signals; second, the signals will be transmitted via the
peripheral nerves to the spinal cord, and then to the thalamus which is
responsible for integrating sensory signals; finally, the emerging
signals from the thalamus will travel to the cortex where the pain
signals turn into conscious perception, and at this moment only, pain
is being perceived.
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The experience of pain triggers emotional response in the patient,
including fear, anger, and anxiety, which the anesthesia team strives
to avoid during surgery. But the process does not end there. Pain is
experienced in the subconscious part of the brain, and triggers
physiological responses, activating the sympathetic system and
thereby the production of adrenaline, which is responsible for pallor,
sweating, rapid heart rate and breathing, and increased blood
pressure. Although the patient does not respond outwardly to surgical
pain while anesthetized, he or she will be under hormonal stress,
which alters the healing process (by mobilizing energy stores instead
of activating repair mechanisms) and leads to an uncomfortable
waking of the patient.
Optimal conditions for general anesthesia require a combination of
general anesthetics to produce unconsciousness and analgesics to
suppress the stress response.
Muscle Relaxation
Muscle relaxation is the last component of the triad model. Sectioning
a muscle of the abdominal wall for example causes a reflex spasm of
the muscle, which renders the abdominal surgery more difficult to
perform. Also, placing a tube in the trachea can only be performed
under deep anesthesia. To circumvent these obstacles, muscle
relaxants are needed both for easy access to the surgery site and
intubation.
Types Of Anesthesia
The nervous system is organized hierarchically. The brain and the
spinal cord constitute the central nervous system (CNS), and function
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to integrate various sensory inputs, process inputs, and elicit
commands to the organs. Surrounding the CNS is the peripheral
nervous system, made of peripheral nerves that convey information
from the different parts of the body to the CNS, and convey signals
from the CNS back to the body. This section highlights the types of
anesthetic drugs and target sites in the body where their effect
happen.1,4-8
Peripheral nerves are made of a mixture of several types of fibers and
each type has a specific function. For each particular nerve, signals
may be heading toward the CNS, known as afferent signals (also
termed ascending), or heading away from the CNS and known as
efferent signals (also termed descending).
Ascending signals are almost all sensory, which include pain,
temperature, touch, vibration and proprioception (joint position
sense). On one side, touch, vibration and proprioception travel through
the type A-fibers, which have a coating of myelin, a lipid that increases
the conduction velocity of the nerve. When they reach the spinal cord,
the signals ascend in structures called the dorsal columns, on the
same side of the body where the signal came from. On the other side,
pain and temperature signals travel in type C-fibers; these fibers have
a smaller diameter and lack myelin, so they have a slower conduction
velocity. These signals travel in the spino-thalamic tracts on the
opposite side of the body from the signal.
Descending signals are used to produce muscle movement; they are
also called motor signals and travel via type A-fibers. Additionally,
other descending signals regulating the function of internal organs
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such as breathing, digestion, heart
rate, bladder control, are below
conscious awareness and depend
on the autonomic system with its
two components - the sympathetic
and parasympathetic pathways.
A nerve cell or neuron consists in a
cell body (“soma”) from which
emerge threadlike extensions or
processes called dendrites and
axons, which are long, slender
projections of the neuron, or
processes that conduct electrical impulses away from the neuron's
soma. Axons can reach up to 1 meter in length. Nerve fibers are made
of nerve cell axons, which can be myelinated or unmyelinated.
An individual nerve transmits its signal along the axons by a selfpropagating electrical charge called an action potential. The interior of
the axon is rich in potassium ions while the exterior is rich in sodium
ions. This state is continually maintained by ion pumps located on the
surface of the axon membrane and this imbalance is what creates the
potential energy.
Opening ion channels in the membrane permits sodium and potassium
to switch places leading to a depolarization lasting a few milliseconds.
In response to this depolarization other channels called voltage-gated
channels are activated to repolarize the cell membrane at this location.
The succession of depolarization and repolarization allows the
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propagation of the impulse to spread along the axon, in what is called
action potential. The action potential is then passed from neuron to
neuron at the synaptic junction where it triggers the release of
chemicals or neurotransmitters. At this level, another action potential
mediated by the binding of the neurotransmitter to the dendritic site of
the synapse will be initiated and so on.
Several substances found in nature are known to disrupt the
propagation of action potentials. The most widely known compound
that interferes with nerve conduction by blocking the voltage-gated
sodium channels is cocaine, the first anesthetic drug.
Cocaine And Derived Pharmacological Products
Cocaine is an alkaloid found in the leaves of the coca plant
(erythroxylum coca) native of South America. The Spanish brought the
plant to Europe in the 16th century and cocaine was for the first time
isolated in 1855 by Friedrich Gaedcke. Later, it was even incorporated
into tonic drinks like Coca-Cola in 1866. Cocaine acts at two levels of
the nervous system. Firstly, it blocks the voltage-gated sodium
channels in the peripheral neurons making it an efficient local
anesthetic agent. Secondly, cocaine acts on the central nervous
system by blocking the reuptake of stimulatory neurotransmitters like
dopamine, serotonin and noradrenaline in the synapses.
Normally, stimulatory neurotransmitters are recycled back into the
transmitting neuron by a specialized protein transporter; if cocaine is
present in the body, it attaches to the dopamine, serotonin or
noradrenaline transporters and blocks the normal recycling process,
resulting in a buildup of these stimulatory neurotransmitters in the
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synapses. This has the effect of enhancing their actions. It is this
second action that is responsible for both cocaine’s stimulant and
addictive properties.
In 1904 at the Pasteur Institute, Ernest Fourneau was able to
synthesize amylocaine and completed a successful search for another
drug having similar anesthetic properties without the addictive side
effect. Since then, almost all local anesthetic drugs carry the suffix –
caine. Amylocaine and its successors share common biochemical
characteristics. They have a ring-shaped structure joined by a short
linkage that is water-soluble. If the connecting link is an ester group
then the drug will be hydrolyzed in the plasma by
pseudocholinesterase; and, if the link is an amide bond, hydrolysis will
occur in the liver. The greater the length of the connecting amino
groups the greater will be potency and toxicity of the local anesthetic.
Amylocaine and procaine have an ester linkage, which can be broken
down in the bloodstream and so these two drugs are known for their
very short duration of action. They also have been associated with a
higher incidence of allergic reactions due to one of their metabolite,
para-amino benzoic acid (PABA). Eventually, an amide linkage was
substituted for ester, making the molecule more stable and with a
longer duration of action. This latter design led to the synthesis of
lidocaine (in 1943), bupivacaine (in 1963), and ropivacaine (in 1993).
Drugs Used In Local Anesthesia
Because local anesthetic agents act by blocking both sensory and
motor nerve conduction, they produce a temporary loss of sensation
without loss of consciousness or depression of the central nervous
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system. Despite the fact that cocaine has been the first identified local
anesthetic, its effects on the central nervous system, coupled with its
addictive potential, have resulted in a significant decline of its clinical
use. This section summarizes the characteristics of more recently
developed drugs, which are currently used in local, as well as regional
anesthesia. These drugs are procaine, tetracaine, lidocaine,
bupivacaine and ropivacaine.1,4-7
Procaine
Procaine has a short duration of action, causes minimal systemic
toxicity and creates no local irritation. The combination procaineepinephrine decreases its rate of absorption in the bloodstream and
doubles the duration of its action. A 1%-2% solution is used for nerve
blocking in regional anesthesia and infiltration anesthesia, and a 5%20% is needed for spinal anesthesia. Procaine is not efficient for
topical use.
Tetracaine
Tetracaine is approximately 10 times more potent and more toxic than
procaine. Its onset of action is about 5 minutes and its effect lasts
between 2 and 3 hours. A 2% solution of tetracaine is used topically
on mucous membranes.
Lidocaine
Lidocaine also known under the name xylocaine is rapidly absorbed,
has a rapid onset of action, and causes minimal local irritation. It is
more potent and has a longer duration of action than procaine. A 0.5%
solution is used for infiltrative anesthesia, while a 1%-2% solution is
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needed for topical mucosal and nerve block anesthesia. Lidocaine is
also available as an ointment, jelly and cream.
Bupivacaine
Bupivacaine is used mainly for regional anesthesia in concentrations
ranging between 0.25%-0.75%. Its toxicity is similar to that of
tetracaine. Its undesirable effects include hypotension, bradycardia,
and prolonged duration of motor impairment, cardiotoxicity and central
nervous system toxicity, which can be fatal. These severe side effects
occur after an overdose or accidental intravascular injections.
Ropivacaine
Ropivacaine is nearly identical to bupivacaine in onset, quality and
duration of sensory block, but it produces lesser duration of motor
blockade and has a better safety profile.
Adverse Effects of Local Anesthetics
Systemic adverse effects of local anesthetics result from the passage
of toxic amounts of local anesthetics into the bloodstream. As a
consequence, epinephrine is prescribed in addition to the local
anesthetic whenever possible to reduce the rate of systemic absorption
and thus the systemic toxicity. Although rare, allergic reactions to local
anesthetics have been observed. Certain local anesthetics, such as
procaine and tetracaine, are associated with a higher incidence of
allergic reactions due to their metabolite para-amino benzoic acid
(PABA).
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Local Anesthesia: Topical and Subcutaneous
Local anesthetics penetrate healthy skin poorly. Therefore, applying
them as creams or gels is not the most effective way to administer
local anesthetics. However, there are preparations such as tetracaine
or lidocaine/prilocaine, which are used to anesthetize the skin in
certain circumstances; for example, prior to blood sampling in the
pediatric population.
In contrast to the skin, mucous membranes absorb topical anesthetics
well. By example, the use of topical anesthetics is effective in
ophthalmic procedures or surgeries. Eye drops of tetracaine can
provide effective corneal anesthesia prior to the extraction of foreign
objects from the eye, or even during prolonged ophthalmic surgeries
involving extra-ocular muscles. Finally, infiltrative anesthesia is
another technique for local anesthetics. Here the anesthesia is injected
subcutaneously. This procedure is well-suited for minor surgeries such
as suturing a superficial wound.
Regional Anesthesia
Regional anesthesia is obtained by blocking a nerve, so that the skin,
the deeper structures, and the muscles that the nerve supplies
become paralyzed. Regional anesthesia results in an inability to move
muscles or to sense pain. Regional anesthesia affects temperature in
the area of the affected nerve.
There are two main categories of nerve blocks. The first called
neuraxial block involves the spine and can be subdivided in spinal,
epidural and caudal block. The second called peripheral block may
involve the eyes, breast, trunk, the upper extremity and the lower
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extremity. Peripheral blocks can be used alone or in combination with
neuraxial anesthesia or general anesthesia.
Another alternative technique of regional anesthesia consists in the
intravenous injection of anesthetic into a limb, which is isolated from
the circulation by application of a tourniquet and is called Bier’s block.
Advantages of Regional Anesthesia
Besides controlling pain, regional anesthesia presents a number of
advantages. It allows the patient to breathe independently without
airway support, reduces postoperative nausea and vomiting, blocks
the stress-induced inflammatory response to surgical trauma, and
avoids airway manipulation in difficult cases. Since regional anesthesia
is accompanied with vessel dilation and lower pressure within the
dilated vessels, there will be less blood loss and less requirements for
blood transfusions. In addition, regional anesthesia allows earlier
recovery of bowel function as well as earlier rehabilitation and hospital
discharge.
General Technique
The technique of regional anesthesia involves inserting the needle near
enough to a nerve to deposit the anesthetic agent without injuring the
nerve itself. For this, it is possible to rely on anatomical landmarks to
locate the nerve, but anatomical landmarks may vary from one
individual to another. Today, the nerve is located using the help of
electronic nerve stimulators, which are more accurate and save time.
A small electric current is passed down the needle and, as the nerve is
approached, the current causes the muscles innervated by the nerve
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to twitch. This signals to the operator that the tip of the needle is close
enough to the nerve.
Another way to avoid nerve and large vessel injuries during the
injection is the use of portable ultrasound scanners, which allow a
guided nerve block under direct visualization of the neighboring
structures as the needle approaches its target. These two techniques
complement each other since they provide important information
about both nerve anatomy and function. Therefore, they are used in
combination by many anesthesia teams.
Before the regional anesthesia procedure begins, the patient is
positioned and connected to standard monitors for follow-up of vital
signs the same as if the patient were receiving a general anesthesia.
The patient is sedated in small doses to maintain the patient’s comfort
but maintain the patient’s consciousness since the patient’s ability to
communicate throughout the surgery is important to maintain block
safety. For lengthy procedures, a plastic catheter may be inserted and
left in situ, so that repeated injections, or an infusion of anesthetic
may be given.
Regional blockade occurs slowly, and may take up to 30 minutes after
the injection to be fully effective. Regional anesthesia is not always
reliable in providing a complete analgesia during surgery. Therefore,
for some types of surgeries, regional blockade is performed as an
addition to general anesthesia. In this case, the regional block placed
first is followed by induction of general anesthesia. This block can also
provide pain relief after surgery if a nerve catheter is left in place for
injection after the patient recovers from general anesthesia.
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Neuraxial Block Procedure
A neuraxial block is also known as spinal block, subarachnoid block,
intradural block or intrathecal block.12-15 The spinal cord is a very
delicate structure. It is covered by a microscopic layer called the pia
mater, and is suspended in clear watery fluid, the cerebrospinal fluid,
which circulates around it. The cerebrospinal fluid is enclosed by
another fragile membrane, the arachnoid, which in turn is enclosed in
a tough membrane called the dura mater.
In spinal anesthesia, local anesthetic is injected into the subarachnoid
space located between the pia mater and the arachnoid, using a fine
needle, usually 9 cm (3.5 in) long. Spinal anesthesia provides a dense
block of all spinal cord function below the level of the block. This
includes loss of motor and sensitive function as well as loss of
automatic reflexes that control blood pressure and heart rate
depending on the level of the block. The head and the body are
unaffected and the patient remains awake.
The height or level of the block depends on the injection site, which is
usually done in the lumbar area, but also on the diffusion of the
anesthetic solution in the cerebrospinal fluid (CSF). To prevent a
higher than intended diffusion of the anesthetic drug, some solutions
for spinal anesthesia are formulated with 8% dextrose, making them
denser (hyperbaric solutions) than CSF. After injection, the patient will
be positioned according to gravity in order to control the height of the
block.
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Dermatome Map
There are eight cervical nerves, twelve thoracic nerves, five lumbar
nerves and five sacral nerves. Each of these nerves relays sensation
from a particular region to the brain. A dermatome is an area of the
skin supplied by the sensory fibers of the spinal nerve. In the head and
trunk, each segment is horizontally disposed, except C1, which does
not have a sensory component.8
Assessment of Neuraxial Blockade Level
Knowledge of dermatome levels is key in allowing the anesthetist to
assess the level of blockade. Spinal nerves contain both sensory and
motor pathways, as well as autonomic fibers. In general, small
myelinated fibers are more susceptible to blockade than larger
unmyelinated fibers. Moreover, with a neuraxial block there is a
difference between sympathetic, sensory and motor block level. The
sympathetic level being generally two to six dermatome levels higher
than the sensory level. The sensory level is approximately two
dermatome levels higher than the motor level.9
Contraindications
Contraindications should include patient refusal, infection, abnormal
coagulation, and cardiac disease. The use of neuraxial anesthesia in
patients with pre-existing neurologic disorders, such as multiple
sclerosis is not recommended unless it is absolutely necessary.
Indications of Spinal Anesthesia
Spinal anesthesia is used for almost any procedure of the lower half of
the body, including orthopedics, obstetrics, and prostate surgery. The
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use of spinal anesthesia has also been described for surgeries in the
head and neck where punctures performed between the 1st and 2nd
thoracic vertebrae resulted in good analgesia. Laparoscopic surgeries
such as laparoscopic cholecystectomy performed under spinal
anesthesia require very small incisions, produce less pain and result in
shorter hospital stays. They are particularly advantageous to use in
older and high-risk patients for general anesthesia.10 In the same
manner, spinal anesthesia has been associated with a lower
postoperative mortality risk in elective total joint replacement
surgery.11
Spinal anesthesia is generally preferred over a general anesthesia in
the obstetric population, as long as it is not contraindicated. The dose
of local anesthetic is often reduced to one-third due to changes in the
intra-abdominal pressure and effects of hormones, which increase
sensitivity.
Drugs and Associated Factors Influencing Effect
The level and duration of spinal anesthesia are primarily determined
by 1) baricity (the density of the drug as compared to the density of
human cerebrospinal fluid), 2) contour of the spinal canal, and
3) patient position in the first few minutes after injection. To optimize
lordosis, a pillow is placed under the patient’s knees; the other option
is to place the patient in the lateral position. Isobaric solutions
undergo less spread than hyperbaric solutions, and both of these
solutions are suited for perineal or lower extremity surgery. Hypobaric
solutions (sterile water or normal saline) are rarely used due the
osmotic stress they might cause.
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Short Duration Procedure
Lidocaine, with duration 60-90 minutes, provides good sensory and
motor block. The dose of lidocaine used is between 60-75 mg.
Lidocaine has been linked to transient neurologic symptoms in up to
one-third of patients. Lidocaine gives less vasodilation.
Longer Duration Procedure
Bupivacaine is the most commonly used local anesthetic. It decreases
spinal and dural blood flow, and 2 to 3 ml of 0.5% in the cerebrospinal
fluid provides about 2 hours of surgical anesthesia. It is administered
at similar dose and duration as tetracaine (5-20 mg with duration of
90-120 minutes). However, bupivacaine gives a slightly more intense
sensory anesthesia (and less motor blockade) than tetracaine.
Tetracaine provides slightly more motor blockade (although less
sensory anesthesia) than bupivacaine. Its duration of action is more
variable than bupivacaine. And since tetracaine is accompanied by
important vasodilation, it is more profoundly affected by
vasoconstrictors.
Spread of anesthesia is affected by the addition of vasoconstrictors; so
the addition of epinephrine (usually 0.1 – 0.2 mg of epinephrine, i.e.,
0.2 to 0.5 cc of 1:1000, or 2 – 5 mg phenylephrine) may be
considered to prolong and/or improve the quality of the block.
Opioids (usually fentanyl 25 μcg) and morphine (0.1 – 0.5 mg) can be
added to provide 24 hours of relief, but unlike fentanyl, morphine
requires in-hospital monitoring for respiratory depression.
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Technique
Spinal anesthesia is one of the oldest techniques in anesthesia. Its use
to produce surgical anesthesia dates back to 1899, and was reported
in a classic paper by a German surgeon Augustus Bier.
Spinal anesthesia is considered as a routine part of any anesthetist
skills. The technique of administering spinal anesthesia can be
described as the “4 P’s”: preparation, position, projection, and
puncture. The use of a rigorous aseptic technique during both the
preparation and the procedure itself must be the rule, as reviewed
further below.12-15
Preparation
Preparation refers to the preparation of the material necessary for the
procedure based on the type of planned surgery and patient’s
characteristics (general status, associated pathologies).12 The
anesthetist will then be able to choose the appropriate anesthetic drug
and formulation (hypobaric, hyperbaric, or isobaric), to match the
proposed length of the surgical procedure.
Prepackaged spinal kits are normally used or can be custom made. If a
prepackaged spinal kit is not available, the following equipment needs
to be assembled:

Sterile towels

Sterile gloves

Sterile spinal needle

An introducer needle if using a small gauge needle (this can be a
sterile 19 gauge disposable needle)

Sterile filter needle to draw up medications
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
Sterile 5 ml syringe for the spinal solution

Sterile 2 ml syringe with a small gauge needle to localize the
skin prior initiation of the spinal anesthetic

Antiseptics for the skin (such as betadine, chlorhexidine, methyl
alcohol)

Sterile gauze for skin cleansing and to wipe off excess antiseptic
at needle puncture site

Single use preservative free local anesthetic ampoule made
specifically for spinal anesthesia
Local anesthetics from multi-dose vials or those that contain
preservatives should never be used for spinal anesthesia. Prior to
initiating a spinal block, the clinician’s hands must be carefully washed.
The patient should be attached to standard monitors including
electrocardiogram, blood pressure, and pulse oximetry, and an initial
set of vital signs should be recorded. Access to an intravenous route
should be ensured.
Positioning of the Patient
Proper positioning of the patient is essential for a successful block.
There are three positions used for the administration of spinal
anesthesia: lateral decubitus, sitting, and prone. In lateral decubitus,
the patient is positioned with their back parallel with the side of the
operating table. Thighs are flexed up, and the neck is flexed forward in
a fetal position. The patient should be positioned to take advantage of
the baricity of the spinal local anesthetic. The seated position is used
for anesthesia of the lumbar and sacral levels required by urological or
perineal surgeries. The patient should be sitting up straight, with feet
on a stool, head flexed and arms hugging a pillow. For a lower
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lumbar/sacral block, the patient is left sitting for 5 minutes before
assuming a supine position. The prone position is used when the
patient will be in this position for the surgical procedure such as rectal,
perineal, or lumbar procedures.
Approaches to Access Subarachnoid Space
There are two approaches to access the subarachnoid space: the
midline and paramedian approach. The midline approach is easiest and
passes through less sensitive structures. The patient is sitting up
straight and with proper positioning to give access to L2-L3, L3-L4, L4L5, and L5-S1. After identification of the top of the iliac crests, Tuffier’s
line, a landmark for the placement of spinal or epidural needle, which
meets the body of L4 or L4-L5 interspace, is drawn across the iliac
crest. Whereas, the paramedian approach is better suited for narrow
interspaces or difficulty with flexion, and typically is located 1 cm from
the midline. The advantage is that by placing the needle laterally, the
anatomical limitation of the spinous process is avoided. The most
common error when attempting this technique is being too far from
the midline, which makes encountering the vertebral lamina more
likely.
Puncture
All precautions should be taken during the step that involves spinal
puncture to preserve a sterile environment. The clinician should wash
hands, put on sterile gloves, and use sterile technique. The tray should
be prepared in a sterile fashion. The patient’s back should be prepped
with an antiseptic. A skin wheal of local anesthetic is placed at the
intended spinous interspace.
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Smaller gauge needles will require an introducer to stabilize the
needle. The introducer is placed firmly into the interspinous ligament.
Grasping the introducer with one hand, the anesthetist should hold the
spinal needle like a dart/pencil. Cutting needles should be inserted
with the bevel parallel to the longitudinal fibers of the dura. This helps
reduce cutting fibers and enhances tactile sensation as anatomical
structures are crossed. Anatomical structures that will be transversed
include skin, subcutaneous fat, supraspinous ligament, interspinous
ligament, ligamentum flavum, epidural space, and dura.
Monitoring During Spinal Anesthesia
After successful placement, the patient should be monitored
continuously for block progression and complications. The first 5-10
minutes are critical in terms of monitoring the cardiovascular response
as well as the level of progression of anesthesia. The patient’s blood
pressure should be taken every 3 minutes, initially. The patient should
be monitored for the following:
Block Progression:
The anesthetist has to ensure that the block is adequate for the
surgical procedure and does not progress too high. Numbness of the
arms and hands and breathing problems may indicate that the block is
too high. High spinals are often accompanied by hypotension, nausea,
and agitation.
Hypotension can be severe enough to cause stroke so it should be
treated aggressively if blood pressure decreases by 20% or more from
baseline. Bradycardia should be treated aggressively as it may
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progress to cardiac arrest. A change in the level of consciousness
“total spinal anesthesia” is accompanied by loss of consciousness.
Measures to prevent high spinal spread:

Use “Heavy” Bupivacaine (0.5% + 8% dextrose)

Inject slowly at L3/4 or L4/5

Inject correct dose (≤ 2mls)

Head elevated on pillow

Monitor rising spinal level
Emergency treatment in case of high spinal spread:

Raise the Blood pressure aggressively with vasopressors

Bradycardia is treated with atropine and ephedrine, adrenaline in
severe cases

Intravenous fluids, colloid solutions, oxygen

Intubate and ventilate if loss of consciousness
Postoperative Care Monitoring:
Patient’s recovering from a spinal anesthesia should receive the same
vigilant monitoring as the patient recovering from general anesthesia.
Patients may experience some level of hypotension in the
postoperative period too. Treatment includes a Trendelenburg position,
additional intravenous fluids, oxygen, and vasopressors as needed.
Urinary retention should be assessed in patients that do not have a
urinary catheter. The patient should not be discharged from the
recovery area until vital signs are stable and the spinal block is
regressing. The patient should remain in bed until full sensory and
motor function has returned. The first time a patient is ambulated, the
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patient should be assisted by a medical or nursing clinician to ensure
full function has returned.
Epidural Anesthesia And Analgesia
This section provides a specific focus on the combination of epidural
anesthesia and analgesia medication for the critical management pain
control and patient cooperation during a surgical procedure. The
epidural (or extradural) space is a potential space surrounding the
outer envelope of the spine, which contains loose fat tissue and veins.
The injection of local anesthetics in the epidural space creates a less
pronounced block than a spinal injection. The anesthetics will target
the spinal nerves on their path out of the vertebral canal. Myelinated
nerve fibers (type C-fibers) are more resistant to local anesthetics.
This means that unmyelinated sensory nerve fibers, which carry pain
signals, are blocked earlier and more completely than myelinated
fibers. This explains why a moderate dose of anesthetic will produce
analgesia without impairing the motor and touch function. However, to
obtain a dense block much like a spinal, one would need a dose about
ten times greater than the dose required for a spinal.1,4-8,12-19
Neural Blockade
As with spinal anesthesia, a number of parameters determine how far
neural blockade will spread after epidural injection. Some variables are
intrinsic to the patient’s anatomy; others depend on variations in the
techniques and the drugs given. The combination of all of these
variables can make the spread of the solution in the epidural space
unpredictable.
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Epidural analgesia is commonly indicated during labor and childbirth
because it provides pain relief while still allowing the mother to push
with her pelvic muscles when needed (at this stage the anesthetist has
to simply discontinue the anesthetic infusion). Also, when labor does
not proceed as expected and a cesarean section is planned in an
emergency, the anesthetist needs only to inject a more concentrated
local anesthetic to achieve a denser anesthesia to the lower abdomen
for the surgical incision.
In addition to obstetrics indications, any lower limb procedure such as
hip replacement, knee replacement or fracture repair can benefit from
epidural anesthesia. Furthermore, epidural analgesia has proved useful
during the recovery from surgeries performed under general
anesthesia such as, upper abdominal or thoracic procedures which can
be quite painful. In this scenario, epidural anesthesia has been shown
to provide a better postoperative pain management than opioids or
morphine, in the same time it decreases postoperative ileus and
improves patient recovery. The latter advantages are particularly
important in elderly patients as well as in patients with pre-existing
pathologies.
Types of Epidural Anesthesia
Single-shot technique is easiest and provides the most uniform spread
of anesthetic. Always begin with a negative aspiration and a test dose
(3 ml of 1.5% lidocaine with 1:200,000 epinephrine) followed by a 3
minute waiting period. If the test dose is adequate, the total amount is
injected in fractionated aliquots of 5 ml each.
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Continuous epidural techniques involve placement of a catheter 3-5 cm
beyond the needle (any longer than has the risk of penetrating into a
vein, exiting the foramen, or wrapping around a nerve root). In a
standard technique the catheter can be left in place for up to 72 hours
and the retrieval of the catheter should never be done through the
needle due to the risk of nerve transection.
Caudal blocks are epidural injections placed through the
sacrococcygeal ligament and sacral hiatus, absent in 10% of patients.
The technique consists in passing the needle through the ligament
until it hits the sacrum, and then retracting slightly before aiming
cephalad (towards the head), and then readvancing 2 cm and injecting
air; if no crepitus is felt, it is likely placement is in the caudal canal and
the anesthetist can inject. As with all neuraxial procedures, caudal
block should be executed with a rigorous aseptic technique.
Duration and Influencing Factors
Dose and volume are important for epidural anesthetics, while
concentration is not. By decreasing concentration and increasing
volume, one can obtain greater anesthetic spread.
In contrast to spinal anesthesia, baricity does not matter in epidurals,
but negative intrathoracic pressure does in terms of levels. Lumbar
epidurals tend to flow cephalad due to negative intrathoracic pressure,
whereas thoracic epidurals tend to stay in place. L5/S1 anesthesia is
more difficult, likely due to the large fiber size. Chlorprocaine is used
for rapid onset and short procedures. Lidocaine is intermediate, and
bupivacaine/L-bupivacaine/ropivacaine has slower onset and prolonged
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duration. Tetracaine and procaine are not used because of their long
latency times.
On a practical level, for a one-shot epidural, a 20 cc dose via lumbar
injection is assumed to provide a mid-thoracic level block and then the
volume is adjusted according to the desired level, for example, a
decrease in the volume if only lower dermatomes are the aim.
Bupivacaine produces a significant sensory block with minimal motor
block, as opposed to etidocaine, which has a more pronounced motor
block. Epinephrine at 1:200,000 can prolong a lidocaine block, but not
a bupivacaine block. The mechanism for the latter is unknown; a
decreased blood flow, an intrinsic analgesia provided by epinephrine,
or an increased volume of distribution has been hypothesized.
Adjuvant Medications
Epinephrine (1:200,000 or 5μcg/mL) can prolong an epidural,
especially if chlorprocaine or lidocaine is used. One has to be aware
however that the mild B-stimulation may accentuate the fall in blood
pressure that generally occurs with neuraxial anesthesia. On the other
side, other studies report that the use of epinephrine seem to be
preferable to phenylephrine at an equivalent dose as it has been
shown to preserve cardiac output in contrast to the latter.
The use of opioids can enhance analgesia, with the degree of side
effects largely related to lipid solubility. Morphine (hydrophilic or
lipophobic) injected epidurally stays in place or spreads rostrally
(distribution of medication within the cerebrospinal fluid), whereas
fentanyl (hydrophobic/liphophilic) will be rapidly absorbed.
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Sodium bicarbonate is known to promote a more rapid onset of
epidural anesthesia.
Neuraxial Anesthesia Complications
Neuraxial techniques are generally considered safer than general
anesthesia, particularly in patients with difficult airway management,
elderly debilitated patients and even the premature newborn.
However, several studies demonstrate that the setting in which a
neuraxial block is performed, as well as the technique used, make a
difference in the risk of complications. Adverse effects of neuraxial
anesthesia may be as minimal as discomfort but may have more
serious consequences such as disability or even death.
Hypotension
Hypotension is the most frequent immediate adverse effect. It occurs
in one third of patients, initially due to decreased vascular resistance
but in severe cases it may be due to decreased venous return and
cardiac output. Risk factors for hypotension include arterial
hypertension, obesity, increased fetal weight, chronic alcohol use, and
a high level of blockade. Hypotension may cause intraoperative nausea
and vomiting. Bradycardia may also be present if the block involves
the heart-accelerating fibers (T1-T4 level), or from a decreased venous
return.
A slight head-down position (5-10 degrees) to increase venous return
without altering the spread of anesthetic and the maintenance of an
adequate hydration are able to correct the situation.
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High Blockade or High Spinal
Due to excessive spread of the anesthetic to higher levels of the
dermatome, hemodynamic and respiratory effects are expected to
occur. It can happen both in spinal and epidural anesthesia. A total
spinal blockade is characterized by sympathetic blockade and
respiratory arrest needs immediate and aggressive treatment as
described in the section above on monitoring.
Cardiac Arrest
Cardiac arrest is most frequently seen in spinal anesthesia with an
incidence estimated at 2.73 per 10,000 patients. A high block,
dehydration, deep sedation, and inadvertent intravascular injection of
the anesthetic, are considered risk factors for this complication.
Urinary Retention
Studies have shown that the sensation of urgency to void disappears
30-60 seconds after spinal injection of anesthetic solution; as for the
detrusor muscle, contraction is completely abolished 2-5 minutes
after. Opioid administration also affects bladder function and
contributes to urinary retention.
Urinary retention is a complication which is more common in men
older than 50 years with a history of urologic dysfunction as well as in
anorectal surgery, inguinal hernia repair, hip surgery and
gynecological surgery. Other risk factors include perfusion of large
amount of fluids, the use of long acting anesthetics, and the site of the
injection for epidurals. A lumbar site is more often associated with
urinary retention than a thoracic site. Postoperative urinary retention
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causes unnecessary pain, vomiting, bradycardia, hypotension, and can
be complicated by urinary infection. Bladder catheterization is
recommended in high-risk patients.
Adverse Effects: CNS and Technique
Central nervous system toxicity can occur whereby the initial
excitatory phase is characterized by the onset of facial numbness,
metallic taste and tinnitus followed by agitation or confusion and
seizures. A depressive phase occurs that involves respiratory
depression and coma following the above symptoms. Cardiovascular
toxicity can also occur and is initially manifested by tachycardia and
hypertension followed by hypotension and myocardial depression, and
then by vasodilation and arrhythmias.
Adverse effects due to technique are highlighted below:
Paresthesia
Paresthesia may be experienced as sharp discomfort by the patient,
during the insertion of the needle or the catheter, radiating to the
buttocks, pelvis or legs. In such case, it is recommended to stop
advancing the needle or injecting the anesthetic at the site as it may
result in nerve injury; in fact, this is the main reason that anesthetists
conduct spinal procedures while the patient is still alert to be able to
report such sensations.
Postdural Puncture or Spinal Headaches
Postdural puncture or spinal headaches are postural; they are due to a
leak of cerebrospinal fluid through the hole left by the needle. They are
experienced by the patient while sitting and resolve in a supine
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position. They are less common now due to the availability of smaller
needles for spinal anesthetics injection.
Spinal headaches are treated most successfully with bed rest and an
increase in fluid for 24 hours. If they persist, the next therapeutic
option will be to perform an epidural blood patch, which consists in
drawing blood from the patient and injecting it in the epidural space to
help seal the hole.
Spinal or Epidural Hematoma
Spinal or epidural hematoma is a rare and potentially catastrophic
complication of neuraxial anesthesia because of the nature of the
bleeding into a fixed and noncompressible space. The incidence of
hematoma in epidural anesthesia is about 1 in 50,000 and above 1 in
200,000 in spinal procedures.
The higher incidence of epidural hematoma can be explained by the
increased vascularity of the epidural space. The clinical manifestations
are due to the compression and ischemia of the spinal cord or spinal
nerves; they may include legs or backache, motor weakness and
dysfunction of the rectal and bladder sphincters. In the event of spinal
hematoma, a prompt diagnosis and intervention are critical to ensure
a recovery of the patient. Spinal cord ischemia tends to be reversible
in patients who underwent laminectomy within the 8 hours of onset of
the neurologic symptoms.
Often patients who are candidates for procedures where a regional
technique would be advantageous are receiving anticoagulant or
antiplatelet therapy, for example, pregnant patients with
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preeclampsia, and orthopedic patient under thromboprophylaxis. In
such cases, regional anesthesia can still be safely performed provided
there is appropriate timing of needle placement and catheter removal
relative to the timing of anticoagulant drug administration.
The patient’s coagulation status should be optimized at the time of
spinal or epidural needle or catheter placement and the level of
anticoagulation must be carefully monitored during the period of
epidural catheterization. Indwelling catheters should not be removed
in the presence of therapeutic anticoagulation, as this appears to
significantly increase the risk of spinal hematoma. Vigilance is
therefore again emphasized in monitoring to allow early evaluation of
neurologic dysfunction and prompt intervention.
Although spinal anesthesia seems to be safe to perform in patients
with bleeding disorders (provided there is a platelet count between
50,000 and 80,000) the decision should be based on careful weighing
of the risk of spinal hematoma with the benefits of regional anesthesia
for a specific patient.
Infections
Bacterial contamination can lead to meningitis or to an epidural
abscess, which can cause spinal cord compression. Bacterial meningitis
after a neuraxial anesthesia is rare with an incidence of 0-2 cases per
10,000, and a high mortality rate of 30% even when antibiotherapy
has been applied. Meningitis may be differentiated from postdural
spinal headache based on the presence of fever accompanying the
neurological signs. Streptococcus salivarus, which is regularly present
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in the skin, oral cavity, gastrointestinal and genitourinary tracts has
been found responsible of more than 90% of post spinal meningitis.
Viral contamination may also occur after neuraxial techniques though
they are less frequent and benign.
Inadvertent germ inoculation during neuraxial anesthesia can be
prevented by a rigorous preparation of the injection site with sterile
equipment, and by maintaining a sterile environment.
Failure
The incidence of failure with neuraxial anesthesia is variable and highly
dependent on institutions and patient population, among other factors.
Experienced clinicians might consider it to be around 1%, while
hospital series reported incidences reaching 47%. Block failure in
general can be attributed to one or the combination of the following
parameters: 1) the experience of the operator, 2) the technique,
3) the spreading of the anesthetic agent, 4) the dosing of the
anesthetic solution, 5) the solution itself, which can be ineffective, and
6) possibly related to the patient’s preoperative and intraoperative
management.
Failed Lumbar Puncture
Failed lumber puncture is the only cause that is immediately obvious.
It can be caused by a blocked lumen of the needle, thus the
requirement to check the material before use, by an incorrect
positioning of the patient, or a spine anomaly. Obesity, anxiety and
pain due to the pathology presented by the patient can hamper the
positioning of the patient. Gentle, reassuring handling of the patient,
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light anxiolytic premedication and systemic analgesia can prevent
movement during the procedure. Good knowledge of spinal anatomy
will be necessary to understand the different structures and potential
resistance encountered when orienting and advancing the spinal
needle.
Dosing and Spread
Spinal needle insertion followed with appearance of cerebrospinal fluid
is a prerequisite but not a guarantee of success during lumbar
puncture. The injection of the appropriate dose should be done after
verification that the connection between the needle and the syringe is
firm to prevent a leak. Similarly, unwanted anterior or posterior
displacements of the needle tip during CSF fluid aspiration (a
necessary step before injection) can result in misplaced injection
(spinal versus epidural).
Inadequate spread of the anesthetic solution can stem again from
inadequate positioning after injection, or from anatomical abnormality
such as kyphosis, scoliosis, which could have been anticipated, within
certain limits, by the preoperative examination. Another rare and not
apparent possibility, lies in the presence of septae within the
anatomical supportive structures of the spine, which act as barriers to
the spread of the anesthetic solution. This can result in unilateral
blocks or insufficient cephalad spread despite the appropriate baricity
of the anesthetic solution and the positioning of the patient.
Furthermore, in rare instances, a larger than usual volume of CSF
associated with dural ectasia (widening of dural sac surrounding the
spinal cord) seen in patients with connective tissue disorders, may
limit anesthesia spread.
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In addition to solution density (baricity), which influences the spread
through gravity, a correct location of the site of the injection must be
carefully selected to avoid a too low block or, to the contrary, a
dangerous and unnecessary higher level spread.
Ineffective Drug versus Medical Error
A well-prepared spinal anesthesia procedure including the preparation
of the required material and the verification that it is adequate and
properly functioning should leave no room for confusion in the solution
preparation. Nonetheless, reports of failure have been attributed to the
loss of solution effectiveness due to prolonged storage or induced by
the sterilization process.
Management of Failure
If all the preventive and corrective measures described above do not
lead to a positive outcome, then the anesthetist has to accept the idea
of failure and move to a back-up plan. A back-up plan should have
been already discussed with the well-informed patient during the
preoperative evaluation. The consequences of a failed block that is
discovered in the course of the surgery have more severe implications
for the patient’s safety, not to mention the medico-legal aspects.
Minor Adverse Effects of Regional Anesthesia
Shivering is partly related to vascular dilation and heat loss from the
skin, and possibly due also to the direct effect of anesthesia on the
thermoregulation center. Temperature regulation is a challenge in both
regional and general anesthesia.
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Itching is observed when opioids are injected into the spinal fluid to
control for postoperative pain. Itching may also occur after
intravenous administration of the same drugs.
Intravenous Regional Anesthesia
Intravenous regional anesthesia (IVRA) or Bier’s block is named after
the German surgeon A.G. Bier who described it first in 1908. The IVRA
is a highly popular procedure, versatile and useful in other settings
than the surgical suite, such as in emergency departments during
reduction of limb fractures and dislocations. It is considered safer than
general anesthesia, especially for those patients who are elderly or
carry diagnoses such as cardiac or respiratory disease. This section
briefly highlights the IVRA procedure.1,4,18,19
With this technique, anesthesia is obtained by the intravenous
injection of a local anesthetic, typically, 12-15 mL of 2% lidocaine for
upper extremities, or 30-40 mL of 0.5% lidocaine, in a previously
exsanguinated vascular space, isolated from the rest of the circulation
by two Esmarch bandages used as tourniquets. The exact mechanism
of IVRA is not completely understood. The likely mechanism is that the
local anesthetic, via the vascular bed, reaches both peripheral nerves
and nerve trunks (vasae nervorum), and nerve endings. Diffusion of
local anesthetic into the surrounding tissues, ischemia and
compression of the peripheral nerves at the level of the inflated cuff
may also contribute to the mechanism of IVRA.
Contraindications
Contraindications to this technique are crush injuries, skin infection,
compound fractures, allergy to local anesthetics and severe peripheral
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vascular disease. Disadvantages include incomplete muscle relaxation
(where important) and lack of postoperative pain relief.
Indications
Bier’s block is a widely accepted technique for short duration surgeries
such as wrist or hand surgery, carpal tunnel syndrome, Dupuytren
contractures, and reduction of fractures. Since the duration of
anesthesia depends on the length of time the tourniquet is inflated,
there is no need to use long-acting or more toxic agents. Its
application for longer surgical procedures is however impeded by the
discomfort caused by the tourniquet, which occurs typically within 30
to 45 minutes.
General Anesthesia
General anesthetics act on the central nervous system or autonomic
nervous system to produce analgesia, amnesia or hypnosis. They are
used alone, or most frequently, as we will see, in combination with
other agents to provide an optimal depth of anesthesia. General
anesthesia can be achieved by inhalation of anesthetic gases or
intravenously. Introduced around 1846, ether and nitrous oxide were
the first inhalation anesthetics to be accepted by the medical
community. Beginning with halothane in the 1950s, halogenated
anesthetics replaced the routine use of ether and chloroform.20
Intravenous agents are used mostly for induction of anesthesia but
they can be used also for some other longer procedures, which are
1) Neuroleptanesthesia, where a narcotic analgesic is combined with a
neuroleptic in association with inhalation of nitrous oxide and oxygen,
2) Dissociative anesthesia with ketamine which produces rapid
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analgesia and amnesia while maintaining the laryngeal reflexes, and
3) Preanesthetic medication (also called premedication) which includes
sedatives opioids, tranquilizers, and anticholinergic agents.4,6
Mechanism of Action of Anesthesia Drugs
There are two levels of understanding how the anesthetic agents work.
Firstly, the molecular basis, which addresses what effect anesthetics
have at a molecular level; and, secondly, the anatomical basis, which
focuses on what part of the body they act on.
The molecular basis of anesthesia is complex and still incomplete.
Although, it seems the predominant molecular mechanism lies in a
transmembrane protein called GABAA receptor with five subunits, found
widely in the central nervous system. The five subunits are the
potential binding sites for general anesthetic agents.
The neurotransmitter GABA (gamma amino butyric acid) is inhibitory,
for example, it makes the postsynaptic cell fire less. Specific binding
sites have been identified for volatile agents as well as for intravenous
drugs such as propofol (potent GABA agonist) and etomidate. More
recently, the intervention of the two pore-domain potassium channels,
which are also widely distributed in the mammalian central nervous
system, have been described. Experimental studies with halothane,
isoflurane sevoflurane, and desflurane have shown an enhancement of
potassium channels leading to hyperpolarization of the neuronal
plasma membrane.1,4,20
As for the mechanism of action of other anesthetics, such as Nitrous
oxide, xenon and ketamine, they are likely mediated by N-methyl-D42
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aspartate (NMDA) receptors. Moreover, apart from its well accepted
NMDA blockade, ketamine has been reported to interact with a wide
range of other intracellular neuronal processes. It seems likely that its
hypnotic effects are caused by a combination of immediate channel
blockade of NMDA and HCN1 channels.21
With regard to the anatomic basis of anesthesia action, the
macroscopic level of the neuroanatomy must be considered.
Immobility induced by inhalational anesthetics is produced in the
spinal cord, precisely it is due to a decreased transmission of afferent
noxious information to the cerebral cortex via the thalamus; in
addition, there is an inhibition of the spinal motor response which
explains the reduction of the withdrawal movement. On the other
hand, amnesia and hypnosis (the two other end points of anesthesia)
are mediated by the brain. Inhalational agents have been shown to
depress cerebral blood flow and glucose metabolism.
Amnesia probably involves among other structures, the hippocampus,
amygdala, and the mediotemporal lobe. Hypnosis or unconsciousness
concerns the cerebral cortex, thalamus and reticular formation.1,4,20
Inhalation Agents
Current volatile anesthetic agents are colorless liquids that evaporate
into a vapor, which produces general anesthesia when inhaled. They
are chemically stable and not likely to breakdown into poisonous
products. They can be distinguished from each other by their specific
properties; such as, potency, speed of onset, smell and partition
coefficient, as further highlighted here.1,4,6,18,20
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The potency of anesthetic gases is expressed as minimum alveolar
concentration (MAC) at 1 atmosphere (atm) required to keep 50% of
adults unmoving in response to a standard skin incision. MAC concept
is a useful concept introduced for the first time by Ted Eger, Giles
Merkel and collaborators in 1963. It helps comparing potencies of
different agents. Isoflurane has a MAC value of 1.2%; it means that at
equilibrium, with the concentration of 1.2% of isoflurane in the lungs,
50% of adults will not move in response to a skin incision.
Sevoflurane, on the other hand, is less potent with a MAC of 2% and
desflurane even less with a MAC of 6%. At equilibrium, it is considered
that the lung’s concentration is equivalent to the concentration in the
blood stream, and this in turn is equivalent to the concentration in the
brain. Therefore, the measurement of the volatile agent in the expired
breath of the patient gives a close approximation to the brain
concentration of the anesthetic gas.
The MAC values are additive, so a patient with 0.5% MAC of isoflurane
and 0.5% MAC of sevoflurane is said to have a 1.0 MAC of anesthetic
in total. Since giving more than 1 MAC will result in less than 50% of
adults moving in response to a painful stimulus, it is understood that
MAC correlates with the depth of anesthesia. Interestingly, whereas
immobility is produced around 1.0 MAC, amnesia is produced at a
much smaller dose of typically 0.25% MAC, and unconsciousness at
0.5 MAC. This implies that a patient might move in response to the
surgical stimulus without being conscious or remembering it
afterwards.
Potency has also been shown to correlate with lipid solubility. This
property is known as Meyer-Overton correlation.
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Speed of onset is inversely proportional to water solubility. Desflurane
is the least water-soluble of all agents and has the most rapid onset
and offset. It is followed by nitrous oxide, sevoflurane and isoflurane.
Pungency is not a desirable property for an anesthetic agent during
the induction of general anesthesia. In contrast to isoflurane and
desflurane, sevoflurane has a fruity smell, which makes it more
suitable for inhalational induction.
Partition coefficient is the concentration of an inhalation anesthetic in
blood or tissue is the product of its solubility and partial pressure. This
solubility is commonly expressed as blood-gas (alveolar) or tissueblood partition coefficient. An agent with a blood:gas partition of 2 will
reach twice the concentration in the blood phase as in the gas phase
when the partial pressure is the same in both phases (at equilibrium).
Ether, a very soluble gas, has a very high blood-gas partition
coefficient equal to 12, while a relatively insoluble agent like nitrous
oxide has a coefficient less than 1. Because high solubility constantly
decreases the alveolar gas pressure, the lower the blood-gas partition
coefficient of anesthetic agent then the more rapid the induction with
that agent.
Influencing Factors
Blood-gas partition coefficients are affected by the concentration of
serum constituents such as albumin, globulin, triglycerides and
cholesterol. These molecules bind to anesthetics increasing their blood
solubility.20
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Drug uptake from the lung and delivery to the tissues, particularly the
brain, is increased by a higher cardiac output although this does not
lead to faster induction since the alveolar concentration is lowered by
the high uptake. In contrast, a decreased cardiac output will be
accompanied with a slow uptake, higher alveolar pressure and thus
faster induction. A larger fat compartment in obese individuals leads to
a longer equilibration time after induction and a slower emergence due
the high absorption of anesthetic agents in the fat tissue and their
slow release. Infants and children have a faster rate of induction than
adults; this has been attributed to a larger ratio of alveolar ventilation
to functional residual capacity, a greater delivery to a richer healthier
vasculature, as well as to lower albumin and cholesterol levels.
Halogenated Anesthetics and Other Gases
Halogenated inhalational anesthetics are currently the most common
drugs used for the induction and maintenance of general anesthesia.
Halothane (Fluothane)
The first chlorofluorocarbon to be developed from chloroform in 1951
is halothane. It was once considered an ideal anesthetic agent in that
it was volatile and non-inflammable and had a high anesthetic potency
with a MAC of 0.75%.20,22,23
Pharmacologic Effects of Halothane
Respirations become rapid and shallow with a reduction in the minute
volume causing a reduction in the ventilatory responses to carbon
dioxide; fluothane produces bronchiolar dilation.
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Arterial blood pressure is decreased in a dose-dependent manner;
there is an increase in cutaneous blood flow, and depression of
myocardial contractility. Halothane antagonizes the sympathetic
response to arterial hypotension and decreases cardiac sympathetic
activity, which results in a slow heart rate. Although uncommon,
arrhythmias have been associated with the use of halothane.
As anesthesia deepens, fast, slow voltage electroencephalogram waves
are replaced by slow, high voltage waves. At 1 MAC, the glomerular
filtration drops by 50%.
Halothane causes muscular relaxation by both central and peripheral
mechanisms, increases the sensitivity to neuromuscular blocking
agents, and like all inhalation compounds can trigger malignant
hyperthermia, a very severe complication. It can also depress liver
function and may lead to hepatic necrosis.
Excretion of Halothane
About 70% of Halothane is eliminated through the lungs in the first 24
hours after administration. The remaining is metabolized by the
cytochrome p-450 system in the endoplasmic reticulum of the liver,
which causes hepatic injury.22
Enflurane
Enflurane is a potent anesthetic obtained from the fluorination of
ether; it has a MAC of 1.68%. Enflurane causes mild stimulation of
salivation, produces tracheobronchial secretions and suppresses
laryngeal reflexes. All of these parameters need to be taken in account
during the ventilation of the patient.20
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Like halothane, enflurane produces a dose-dependent respiratory
depression and has similar effects on blood pressure and myocardium
as well as on the renal glomerular filtration. However, bradycardia and
cardiac output are not as much decreased as with halothane. Enflurane
also acts directly on the neuromuscular junction providing adequate
relaxation to the muscles, including uterine smooth muscle. On the
other side, enflurane increases intracranial pressure and produces an
electroencephalic pattern similar to seizure activity or frank seizures.
Therefore, it is contraindicated in epileptic patients. It is eliminated in
80% as expired gas; free fluoride is released and as little as 5% are
metabolized in the liver. Nevertheless, hepatic necrosis cases have
also been reported after repeated administration of enflurane.
Isoflurane
Isoflurane a methyl-ethyl diether-like desflurane, while sevoflurane is
a methyl-isopropyl ether; all of these gases derive from the
fluorination of ether. Isoflurane is actually an isomer of enflurane. It
also produces respiratory depression and a fall in arterial blood
pressure, with the advantage of being a better myorelaxant than
halothane and enflurane. Moreover, unlike enflurane, isoflurane does
not cause seizures; and, unlike halothane, isoflurane does not induce
arrhythmias. For these reasons, isoflurane is the anesthetic of choice
among the halogenated volatiles compounds.20
Adverse Effects of Halogenated Anesthetics
About 25% of halothane is metabolized by oxidative phosphorylation
via hepatic cytochrome P450 systems. The major metabolite is
trifluoroacetic acid (TFA), which is protein-bound and this TFA–protein
complex (neoantigens) has been shown to induce a T-cell-mediated
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immune response resulting in hepatitis ranging from mild to fulminant
hepatic necrosis, and possibly death. According to the National
Halothane Study, the risk of fatal hepatic necrosis is one in 10,000
anesthetic procedures.
Current volatile gases such as enflurane, isoflurane and desflurane are
also metabolized in the liver through the metabolic pathway involving
cytochrome P-450 2E1 (CYP2E1) which produces trifluoroacetylated
components; however, in comparison with halothane, only 2–5% of
isoflurane, sevoflurane, and desflurane are metabolized; the remaining
is excreted unchanged in exhaled air.20
The severity of hepatotoxicity of these compounds is associated with
the degree by which they undergo hepatic metabolism by cytochrome
P-450.20,22 Enflurane, isoflurane, desflurane, and sevoflurane have
different molecular structures to that of halothane and they seem to
be associated with less hepatotoxicity; however, rare cases of acute
liver injury have also been reported with all of these agents. The
pattern of liver injury described with enflurane, isoflurane and
desflurane has common features with that of halothane, and evidence
of autoimmune response to trifluoroacetylated liver proteins has been
reported.20,22
Unlike other halogenated anesthetics, sevoflurane is not metabolized
to hepatotoxic trifluoroacetylated proteins; nevertheless, very few
reports have described liver injury after sevoflurane exposure.
Consequently, a history of anesthesia-induced hepatitis is a
contraindication to halothane or other halogenated anesthetics re-
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exposure. The susceptibility to malignant hyperthermia is another
contraindication.4,18
Nitrous Oxide
Nitrous oxide (N2O) is an inorganic inert, odorless, gas which can be
compressed into a liquid. Although, chemically different (with respect
to their properties) from halogenated gases mentioned above, it has
similar behavior. The MAC of nitrous oxide is 105.2%, which means
that it needs hyperbaric conditions to reach a level of I MAC. For
maintaining anesthesia a concentration of 75%-80% is required.
Although nitrous Oxide is a powerful analgesic that is well tolerated
and has rapid onset of action and recovery, it is a weak anesthetic.
Therefore, to achieve a more complete anesthesia, the use of nitrous
oxide needs to be supplemented by a narcotic agent as well as a
neuromuscular blocking agent. More often, nitrous oxide is used in
combination with other potent anesthetic agents, and because of that
it is probably the most widely used general anesthetic agent.1,6,19
An inhalation of 50:50 mixture of nitrous oxide with oxygen known as
“gas and air” is offered sometimes to women in labor because it is
effective enough to relieve pain without causing general anesthesia.
Moreover, at 50% concentration, its effects on breathing are minimal.
N2O is excreted primarily through the lungs as expired air.1,6
Adverse Effects and Contraindications of N2O
Because of its high partial pressure in blood and its low blood:gas
partition coefficient, N2O diffuses into air–containing cavities and thus
expands the volume of gas in air pockets. This effect can result in
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bowel distension, rupture of a pulmonary cyst, rupture of the tympanic
membrane in the middle ear, and pneumocephalus. In the blood it can
enlarge the volume of air embolus. Therefore, the use of N2O is
contraindicated in bowel obstruction, air embolism and chronic
obstructive pulmonary disease. It can lead to diffusion hypoxia at the
end of anesthesia if a patient starts breathing room air all of a sudden.
An outward movement of N2O causes hypoxia from the tissues to the
blood and then to the alveoli where it decreases alveolar tension and,
by the same token, lowers arterial oxygen levels. To circumvent this
drawback, one has to administer 100% oxygen for a short period of
time at the end of the N2O anesthesia. N2O is also associated with a
higher incidence of postoperative nausea and vomiting and should be
avoided whenever possible in patients with a positive history of
PONV.6,23
Xenon
Xenon (Xe) is odorless and nonirritant to the airway, which favors a
smooth induction; and with a MAC of 71% it is considered as potent
enough to be given alone with oxygen. Its blood:gas partition
coefficient is 0.12, which means that it provides a rapid onset and
recovery from anesthesia. It is a more potent intraoperative analgesic
than sevoflurane.1,20
Xenon produces depression of postsynaptic excitatory transmission via
NMDA receptor block. It has minimal cardiovascular side effects, even
in cases of severely limited myocardial reserve. Although a mild
respiratory depressant, xenon decreases respiratory rate and increases
tidal volume, in contrast to volatile agents. Experimental models
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suggest that it has a significant neuroprotective action, but this benefit
seems to be offset by an increase in cerebral blood flow, which
elevates intracranial pressure.
Xenon causes an increase in pulmonary resistance due to its high
relative density. Because of this, it should be used with caution in
patients with severe chronic obstructive pulmonary disease and
premature infants. It is not metabolized in the liver or kidneys, has no
negative environmental effect and it does not trigger malignant
hyperpyrexia. Despite all these advantages its use is still very marginal
due to higher cost of production and its rapid diffusion through
ordinary anesthetic hoses thus requiring specialized equipment.1,20
Oxygen
Oxygen (O2) is produced by distillation of liquid atmospheric air. At
ordinary temperatures, oxygen cannot be liquefied so it is stored as
compressed gas in cylinders. Medical air is atmospheric air filtered to
remove particles (such as pollen, oil droplets), and dehydrated to
remove moisture then compressed into cylinders. In addition to being
used throughout anesthesia procedure, compressed medical air may
be used in the operating room to power surgical tools. In anesthesia
oxygen is used in combination with air or nitrous oxide but rarely alone
as it can be harmful to the lungs if the administration is prolonged.1,19
Delivery Methods of Inhalation Anesthesia
The three most common methods used to control the airway during
general anesthesia are: the mask (facemask), the laryngeal mask
airway and the endotracheal tube.1,19
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Mask Ventilation
Mask ventilation is performed with proper airway maintenance
maneuvers during induction of general anesthesia. The mask has an
airtight seal around the mouth and nose allowing the patient to breathe
the anesthetic gas mixture efficiently. Ideal mask position is obtained
by lifting the patient’s chin upward positioning the head in the so-called
“sniffing” position and bringing the mandible forward to move the
tongue from the oropharynx.
Mask ventilation can be challenging in neck and head surgeries,
including ophthalmic procedures, as the anesthesiologist and the
surgeon share a focus on the airway. Mask ventilation is frequently
employed in short procedures, when the anesthetist has access to the
patient’s airway or when tracheal intubation is difficult or impossible.
Some studies report an incidence of impossible mask ventilation
ranging between 1.4 to 5 percent.
Sleep disordered-breathing (SDB) in particular has been identified as a
non-negligible risk factor for difficult mask ventilation, given the fact
that the prevalence of SDB is as high as 69% of the general surgical
population. Reports show that patients with SDB who undergo general
anesthesia have pharyngeal airways that are narrower and more
collapsible when compared to non-SDB patients.25,26 Mask ventilation
has changed little in contrast to significant improvement of tracheal
intubation techniques and devices in the past decade.
Laryngeal Mask Airway
The laryngeal mask airway (LMA) is made of soft rubber and is inserted
via the mouth into the back of the throat resting just above the vocal
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cords. Its distal extremity is connected to the anesthesia machine
breathing circuit. Because the laryngeal mask does not penetrate into
the trachea, it is less irritating to the vocal cords and the throat than
the endotracheal tube. However, the LMA tube does not protect against
aspiration pneumonia and ventilation cannot be controlled as reliably as
it can be done with the endotracheal tube.
Endotracheal Tube
Intubation with endotracheal tube
was a major progress in the field of
anesthesia as it has allowed for
controlled mechanical ventilation and
more invasive surgeries. Typically,
the endotracheal tube is placed in the
patient after the induction phase of
anesthesia and will be removed
before awakening. The process by
which the endotracheal tube is
inserted in the trachea is called
intubation. Optimal intubating
conditions are achieved when the tragus of the ear is aligned with the
sternum allowing a direct visualization of the vocal cords while
performing direct laryngoscopy.
The endotracheal tube is made of soft plastic, and is inserted through
the mouth or the nose and guided with a laryngoscope through the
vocal cords into the trachea. The distal end coming out of the mouth is
connected to the anesthesia breathing circuit. A balloon (low pressure
cuff) on the outer portion of the endotracheal tube is positioned inside
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the trachea and inflated to produce an airtight seal between the tube
and the trachea in order to prevent any gastric fluid or secretions from
entering the lungs. The incidence of aspiration pneumonia has been
considerably reduced by the use of cuffed endotracheal tubes. In
preparation for the intubation, the anesthetist’s preoperative evaluation
of the patient should be focused on airway conditions, including mouth
opening, dentition, receding jaw, and limitations in neck anatomy and
range of motion.
Difficult laryngoscopy/intubation has been reported to occur in 5.8% of
general anesthesia;26 various scoring systems based on orofacial
measurements have been used to predict difficulties during intubation.
The most widely known is the Mallampati score, which identify patients
in whom the pharynx is not well visualized through the open mouth. It
may be obtained on a seated patient with the mouth open and the
tongue protruding without phonating. If a predisposing factor has been
detected during this assessment, a more appropriate strategy for
intubation should therefore be planned.
Intravenous Induction Agents
As opposed to anesthesia, analgesia is the relief of pain without loss of
consciousness. This section covers combination anesthesia and pain
medications used during the anesthesia induction phase.1,6,19-21,27-29
Morphine is the most abundant analgesic opiate found in opium; it is
extracted from the poppy seed and is a potent pain reliever. Opioid on
the other side is a term used in reference to both naturally occurring
opiates and synthetic drugs having similar actions. Opioid substances
impair pain sensation through opiate receptors of several types that
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have been identified in the central nervous system. These receptors
are found in:

The limbic system, including the hypothalamus

The medial and lateral thalamus and the area postrema, site of
the trigger zone for nausea and vomiting (emesis)

The nucleus of the solitary tract, location of the cough center

The spinal cord
Neuroleptanesthesia
A combination of a neuroleptic (also called antipsychotic or major
tranquilizer) with a powerful narcotic is used to provide
neuroleptanalgesia; and, the addition of nitrous oxide and oxygen to
the combination of neuroleptic/narcotic agents produces
neuroleptanesthesia.
The most frequently used agents to achieve neuroleptanalgesia are
droperidol, a butyrophenone derivative, and fentanyl, an opioid with a
short duration of action. However, both of them exert a marked
respiratory depressant effect, which outlasts the analgesic effect and
they both induce hypotension. Fentanyl should be administered slowly
over 5 to 10 minutes and adequate ventilation and oxygenation are
required. After neuroleptanalgesia, nitrous oxide administration starts.
This latter method is useful in obstetrics and in minor procedures such
as diagnostic explorations if the patient is cooperative. The most
common adverse effects after neuroleptanesthesia are confusion and
mental depression.
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Dissociative Anesthesia
Dissociative anesthesia is a state similar to neuroleptanalgesia in
which patients feel totally dissociated from their surroundings.
Ketamine is the only drug used at the present time to produce this
state. Ketamine was introduced as a derivative of the hallucinogenic
drug phencyclidine in 1965. It is a very atypical induction agent as it
does not suppress consciousness as most general anesthetics do, but
disrupts it. With ketamine the patient has a rather normal muscular
tone, the eyes may remain open, and by observing the
electroencephalogram tracings it may wrongly be concluded that the
patient is awake.
Ketamine produces profound analgesia and amnesia. Unlike other
agents, skeletal muscle tone, heart rate, arterial blood pressure and
cerebrospinal fluid pressure can be increased by ketamine. Moreover,
ketamine does not affect the laryngeal reflexes and maintains a
normal respiratory cycle with a strong bronchodilator effect. To
counteract ketamine’s known excessive salivation effect, which poses a
potential risk of aspiration in the deeply sedated patient, atropine is
added in the premedication to reduce mucous and salivary secretions.
Several routes including oral, rectal and intramuscular can be used to
administer Ketamine. Its duration of action is between 10 to 20
minutes; therefore, it is commonly used in children and adults for
short diagnostic procedures. Because of its hallucinogen effect,
recovery from ketamine anesthesia is accompanied by emergence
delirium and agitation. Ketamine is contraindicated in patients with
psychiatric disorders, with a cerebrovascular disease, intracranial
hypertension, arterial hypertension and glaucoma.
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Barbiturates
Thiopental:
Thiopental is a short acting barbiturate, brought into practice for the
first time in 1934. Although it provides a rapid and stable induction of
general anesthesia, it is cleared very slowly from the body. So it is not
suitable for maintenance of anesthesia and an alternative volatile
agent must be used for that matter. It also causes a dose-dependent
depression of heart rate and blood pressure.
Etomidate:
Etomidate, which has been introduced in 1973, is an ultra-short acting
hypnotic, which can induce amnesia within 5 to 15 seconds after a
single bolus dose and unlike thiopental, has virtually no cardiovascular
effects. However, it has other drawbacks such as pain on injection,
myoclonic movements at induction, and post-operative nausea and
vomiting especially in combination with opioid use. Its use as a
sedative in the intensive care unit has also been reported to be
associated with suppression of synthesis of endogenous steroids by
adrenal glands. Therefore, etomidate should not be used in the
maintenance of anesthesia.
Propofol
Propofol was introduced in 1985; it is a short-acting intravenous
anesthetic that can induce unconsciousness within 1 minute, but it has
a short-lived effect of 3-5 minutes due to its rapid redistribution. These
properties make propofol suitable for induction and maintenance of
general anesthesia. Moreover, it produces a rapid clear-headed
recovery, which is useful in ambulatory surgery.
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Pre-anesthetic Medications
A well-thought and planned premedication not only will foster an
uncomplicated anesthesia and post-operative course by reducing the
anxiety of the patient, and by improving the rapidity and the
smoothness of induction, but it will also compensate for the side
effects of the anesthetics including salivation, bradycardia, and postoperative nausea and vomiting. Pre-anesthetic medications include
sedatives, opioids, tranquillizers and anticholinergic agents.
Sedatives or barbiturates, such as secobarbital and pentobarbital are
the most commonly used sedatives as they produce less nausea and
vomiting than opioids. Opioids such as fentanyl and morphine are
given to patients in combination with nitrous oxide and thiopental.
They can also be administered with a barbiturate for regional
anesthesia.
Phenothiazine derivatives like promethazine are often administered
with opioids due to their potentiation effects on analgesia without
increasing the side effects. Tranquilizers are useful as preoperative
sedation, and they help to prevent central nervous system stimulation
caused by the local anesthetics and provide amnesia. Anticholinergic
agents such as atropine and scopolamine are commonly used to
reduce salivation.
Muscle Relaxants/Neuromuscular Blockers
They are valuable adjuncts to general anesthesia and should be
administered only to anesthetized patients. They should not be used to
stop patient’s movement because they have no analgesic or amnestic
effect.
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Neuromuscular blockers act at the neuromuscular junction via their
effects on acetylcholine, which is the major neurotransmitter at the
motor endplate. There are two levels of action; the post junctional
effects such as those produced by depolarizing neuromuscular blockers
like succinylcholine (which consist in a prolonged depolarization by
desensitization of acetycholine receptors), inactivation of voltagegated sodium channels at the neuromuscular junction, and increases in
potassium permeability of the cell membrane, resulting in a failure of
action potential generation and muscular block. As for the
prejunctional effects, they are produced by nondepolarizing
neuromuscular blockers, which affect the receptors on motor nerve
endings involved in the modulation of acetycholine release and
preventing it from being made available.
The main advantages of neuromuscular blocking agents are
improvement of face mask ventilation and facilitation of tracheal
intubation. They also provide surgical relaxation. The required
intensity of neuromuscular blockade that is desired depends on the
type of surgical procedure. There are, however, important safety
issues with their use due to their cardiovascular and respiratory side
effects.
Succinylcholine, a rapid onset, short-acting depolarizing muscle
relaxant has been traditionally used when rapid tracheal intubation is
needed in emergency or during an elective surgery. It can provide
muscle relaxation in 60 to 90 seconds and its effect lasts only 6 to 10
minutes. However, it has numerous side effects, which include severe
effects such as cardiac arrest, severe arrhythmias, prolonged
respiratory depression, and malignant hyperthermia. Further, it is
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contraindicated in patients with known hyperkalemia, major crush
injuries, and muscular dystrophy. Succinylcholine has also been
associated with increase in intracranial and intraocular pressures.
Intermediate-acting neuromuscular blockers include steroid-based
compounds, pancuronium, vecuronium, atracurium and cisatracurium;
however, none is as rapid as succinylcholine. Rocuronium, which is
also a steroid based non-depolarizing muscle relaxant, has been
proposed as a replacement for succinylcholine. However, due to its
longer duration of action (37 to 72 minutes), rocuronium has to be
used with caution in patients with myasthenia gravis, hepatic disease,
neuromuscular disease, severe cachexia and carcinomatosis. Allergy is
the only contraindication to the use of rocuronium.
Except for the relatively new drugs atracurium and cisatracurium, the
kidney generally excretes muscle relaxants that are metabolized in the
plasma (Hofmann elimination), and thus can be used in case of renal
or hepatic impairment.
Reversal of Neuromuscular Blockade
The neuromuscular blockade induced at the beginning of the general
anesthesia needs to be reversed at the end of surgery with the use of
anticholinesterases drugs which act primarily by inhibiting
acetylcholine esterase, thus prolonging the existence of acetylcholine
at the motor endplate. Neostigmine, a commonly used reversal agent,
is administered at 60-80 μg/kg and usually combined with atropine to
antagonize the muscarinic side effects of neostigmine.
Sugammadex (modified gamma-cyclodextrin) is a selective relaxant
binding agent which complexes with steroid-based neuromuscular
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blocking agents, helping in rapid removal from plasma and excretion
through the kidney. The recommended dose for sugammadex is
between 2-16 mg/kg of body weight.
To avoid relying only on neuromuscular blocking agents, it is important
to keep in mind that there are other alternatives that will provide
adequate relaxation in the operating room. These options are the
adjustment of the depth of anesthesia, regional anesthesia, and proper
positioning of the patient on the operating table. The anesthetist has a
choice to make depending on the estimated time remaining before the
end of the surgery, the anesthetic technique and the type of surgery.
Intravenous Administration of Fluids
Anesthetists commonly administer intravenous fluids for a wide variety
reasons.4,18, Bleeding is the most obvious one. Patients may also be
dehydrated preoperatively due to the disease, particularly a bowel
disease, or fasting. In such cases the anesthetist must estimate the
patient’s fluid status and correct it if necessary, using urine output if
the patient is catheterized, central venous pressure and blood tests.
Five categories of intravenous fluids need to be mentioned: 1) 5%
Dextrose in water (D5W) is useful because this solution has the same
concentration of the blood plasma. When D5W is administered the
cells rapidly absorb dextrose, which leaves only water in the
circulation. This is therefore an effective way to deliver water to the
body as pure water is harmful causing the cells to rupture.
2) 0.9% normal saline solution (sodium chloride) is commonly used
during surgery for immediate venous/arterial access for intravenous
medication. 3) Compound sodium lactate (Hartmann solution) is
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another salty solution that contains sodium, potassium, calcium
chloride and lactate in levels similar to those of human blood. When a
patient loses blood the most important measure is to maintain the
circulating volume. If blood is not immediately available, saltcontaining solutions are used. However, in this scenario each volume
of blood lost needs to be replaced by twice or three times the volume
of salty solutions due to the fact that they leak out to the tissues over
time. 4) Solutions, known as colloids, containing large molecules like
certain proteins (gelatin) or carbohydrates (dextran) are retained
much longer in the bloodstream and can fulfill the purpose.
Unfortunately, they can be responsible for severe allergic reactions
and also interfere with blood coagulation. 5) Blood products include
red cells fraction, platelets, coagulation factors, and they are replaced
according to the need of the patient.
General Anesthesia Procedure
Before proceeding it is important for the anesthetist to verify that all
the necessary equipment and material needed are available and ready
for use. The mnemonic DAMMIS is a reminder of what should be
checked: Drugs, Airway equipment, Machine, Monitors, IV, Suction
The stages of general anesthesia include:4,18,29

Stage I:
Stage of induction or analgesia

Stage II:
Stage of excitement or delirium (dilated reactive pupil due to the
preponderance of the sympathetic system)

Stage III:
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Stage of surgical anesthesia (normal pupil); it is divided into four
planes (Guedel’s classification). Stage III is the state into which
the patient should be maintained for general anesthesia.

Stage VI:
Stage of medullary paralysis (dilated non-reactive pupil)
General anesthesia has three phases, which are important to consider:
these are the induction, maintenance and recovery phase.
Induction
Induction is the period between the administration of inductions
agents and loss of consciousness where the patient status evolves
from analgesia without amnesia to analgesia with amnesia. It is
considered as the most dangerous time since the medications can
result in hemodynamic instability, apnea and loss of airway tone.
Coughing, breath-holding and laryngospam may occur at this phase.
Overdose or an inadequate choice of medication for induction is one of
the most common causes of death during general anesthesia. A review
of anesthesia-related cardiac arrest based on a database of 217,365
procedures showed that 64% of anesthesia-attributable cardiac arrest
were caused by airway complications that occurred during induction,
emergence or in the postoperative period, with a 29% rate of
mortality. On the other hand, anesthesia-contributory cardiac arrest
occurred during all phases of anesthesia and led to a 70% mortality
rate.
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As seen previously, induction can be performed using either
intravenous route, or via inhalation of an anesthetic gas. The latter
method is used especially in the pediatric population before the
anesthetist can have access to an intravenous route. Intravenous
induction involves also the administration of an analgesic (fentanyl) in
anticipation of the pain the patient may feel during endotracheal
intubation and which may raise the blood pressure and the heart rate.
Since the next step will be to secure the airway, muscle relaxants will
be added to facilitate endotracheal intubation if needed, and thus
mechanical ventilation. However, if during the patient’s preoperative
assessment, the anesthetist has identified predictors of difficult airway
access, then intubation of the patient should be performed before
induction using an advanced tool like a fiberoptic bronchoscope.
After induction, eyelids should be taped gently in a closed position to
avoid corneal exposure or accidental erosion and to prevent nerve
injuries, the patient should be positioned with the arms at less than 90
degrees in relation to the body, padding of the regions in contact with
hard surfaces and a neutral neck position are recommended.
In general, intubation is indicated in an emergent case with a potential
for airway contamination including full stomach, altered state of
consciousness, and polytrauma. In elective surgery, the indication may
be, among other reasons, gastroesophageal reflux, pharyngeal
bleeding, surgical need of deep muscle relaxation with long-acting
muscle relaxants (abdominal or thoracic surgery), and predictable
difficulty to use mask ventilation (i.e., due to facial anomaly, orofacial
surgery, or surgery requiring a lateral or prone positioning of the
patient).
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The induction phase is characterized by an intense and frequent
monitoring of the patient’s parameters. In addition to clinical
observation of the patient, a routine practice is to measure blood
pressure every minute along with a continuous electrocardiogram,
pulse, temperature, oxygen saturation, and end-tidal carbon monoxide
concentrations.
Rapid Sequence Induction
A specific type of induction called rapid sequence induction (RSI),
consists of rapid sequential intravenous administration of an induction
anesthetic, a sedative and a muscle relaxant with or without a
narcotic; this is followed by endotracheal intubation within one minute
of injection of the muscle relaxant (usually succinylcholine due to its
fast onset and duration). RSI is indicated in emergency situations
where the patient is unstable or considered to be at high risk for
aspiration or in elective surgery and if there is increased intracranial
pressure.
Maintenance of Anesthesia
Maintenance of anesthesia is the continuation of general anesthesia
with the use of intravenous or inhalational agents, independently from
the mode of induction. Most frequently, the patient will be kept
anesthetized with the administration of inhalational agents via the
breathing system of the anesthesia machine. The patient may be
breathing spontaneously the oxygen/anesthetic mixture, or artificially
under pressure by a ventilator, particularly if the surgery required the
use of deep muscular blocking agents which indiscriminately impede
the function of respiratory muscles.4,18
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The maintenance phase is usually the most stable part of the
anesthesia process. Nevertheless, the anesthetist should still keep the
same level of vigilance and ensure a regular monitoring of the patient.
The measurement of the blood pressure, respiratory rate, heart rate,
oxygen saturation, temperature, oxygen administration and gases,
end-tidal carbon dioxide, will be recorded. Depending on the type of
surgery and/or preexisting medical conditions of the patient, additional
parameters such as central venous pressure, urinary output will have
to be included.
It is also critical for the anesthetist to stay updated about the progress
of the surgical procedure, as clear communication with the surgical
team supports planning of the next phases of anesthesia. As the
surgical procedure progresses, adjustments in anesthetic doses might
be needed to maintain the required level of anesthesia, while keeping
the patient safe with the minimum amount of medications. The depth
of anesthesia can be estimated via the electroencephalographic (EEG)
recording on the monitor screen, as well as by the bispectral index
monitoring, if available. However, experienced anesthetists should be
able to recognize inadequate anesthesia when the patient moves or
coughs.
If the patient has been administered myorelaxants, the anesthetist
should be alerted by an onset of hypertension, tachycardia, sweating
and capillary dilation and determine whether adjustment of the level of
anesthesia depth is required. Conversely, a decreased heart rate and
hypotension may mean excessive depth and must be corrected
immediately to prevent severe complications.
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It is worth mentioning that the drugs administered during the
induction phase may still continue their effects during the maintenance
phase. Similarly, effects of the drugs used during the induction and
maintenance phase may still be exerting their effect during the
recovery phase. This should be taken into account to estimate the
doses for maintenance and to evaluate possible adverse effects due to
drug interactions.
Recovery from Anesthesia
Recovery from anesthesia, also called the emergence phase, is
planned in collaboration with the surgeon as the surgery is drawing to
a close. Again, vigilance and close monitoring by the anesthetist of all
the parameters are of paramount importance during this critical phase,
which is marked by exacerbated autonomic responses and
instability.4,19,30-33
First, the anesthetic gas administration level is lowered or even
interrupted. Assisted ventilation is stopped and the patient is restored
to breathing independently and progressively emerging to
consciousness. In a second step, if muscular blocking agents were part
of the anesthesia regimen their action is reversed. Traditionally,
anticholinesterases drugs (neostigmine) have been used to reverse
this action. However, their efficacy has not been consistent in resolving
deep levels of neuromuscular block. A more selective agent
sugammadex is now available. Concurrently, the regression of muscle
paralysis should be monitored and its reversal objectively assessed.
Clinical evaluation of the muscle blockade relies on the return of
muscle strength (head lift, jaw clench and grip strength) or respiratory
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parameters (vital capacity and tidal volume). However, clinical signs
are not considered sensitive enough to serve as criteria upon which
the anesthetist should base his/her decision to extubate the patient.
Therefore, the prevalent opinion within the medical community is more
in favor of using a peripheral nerve stimulator to evaluate the
blockade. Most commonly, the anesthetist will observe the contraction
of the adductor pollicis muscle elicited by the stimulation of the ulnar
nerve either at the wrist or at the elbow. If patient positioning limits
access to the arms to stimulate the ulnar nerve, then the peroneal
nerve or the facial nerve may be used for monitoring.
Objective evaluation of the depth of neuromuscular blockade is
important for the determination of the appropriate dose of
sugammadex to be administered, as well as the timing of tracheal
extubation to ensure no residual weakness is present at the end of the
anesthetic procedure.
Postperative residual neuromuscular block has been associated with
impaired pharyngeal function, increased aspiration risk, upper airway
weakness and partial upper airway obstruction. It can considerably
jeopardize the recovery of the patient as it has been shown to lead to
postoperative pulmonary complications in 28% of the cases and even
to tracheal reintubation. Therefore, regardless of the clinical
experience of the anesthetist, objective assessment of neuromuscular
function has become mandatory.
Once the patient has regained his/her airway reflexes, the anesthetist
will proceed with extubation and observe/monitor the patient until
complete stabilization and communication by the patient is made. If
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the procedure was performed in an ambulatory setting, under no
circumstances should the patient be allowed to leave the health facility
unaccompanied or drive on the same day of having a surgical
procedure.
Total Intravenous Anesthesia
Total intravenous anesthesia (TIVA) is defined as a procedure that
achieves general anesthesia without inhaled hypnotics. This method
has several advantages. It is generally quicker and easier to perform
in a patient who does not need to be intubated.1,4,18
Main Indications of TIVA

Risk of malignant hyperthermia

Long QT syndrome

History of severe postoperative nausea and vomiting

Tubeless Eye nose and throat, and thoracic surgery

Patients with difficult intubation/extubation

Neurosurgery patients

Neuromuscular disorders/myasthenia gravis

Ambulatory exploration or surgery
Criteria for Pharmacologic Agents and System Requirements for TIVA
Drugs with fast onset and offset times are preferred because they
balance hypnosis and analgesia with rapid recovery. For example, the
co-administration of propofol and remifentanyl are synergistic and
considered a good drug combination. The use of target-controlled
infusions is key for the maintenance of adequate concentrations both
in the brain and the plasma, and the best way to achieve this level is
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with pharmacokinetic infusion pump systems.1 Target controlled
infusion systems have the following components: 1) a user interface,
2) a microprocessor with pharmacokinetic software, 3) an infusion
pump which delivers up to 1200 ml/hr, and 4) a visual and audible
alarm system.
Preparing And Planning For Anesthesia
When the need for and type of anesthesia is being considered, the
patient interview with the anesthetist is a very important step. This is
particularly true in elective surgery. It will bring to light the patient’s
temperament, mental status, level of cooperation, personal habits,
history of addictions (with their potential to interact with the anesthesia
drugs), and allergic antecedents. The patient’s family history is also very
important; for example, family history may include malignant
hyperthermia in a parent or sibling, which is crucial to help guide the
patient make an informed decision about the choice of anesthesia and
agents that should be avoided.18,23,25,53,58,59,60-63
A pertinent assessment related to pathological conditions in the
patient’s personal history with potential to lead to difficult airway
management during anesthesia gives certain cues as to what would be
required for airway management. For example, a positive history for
gastroesophageal reflux disease, dysphagia, and gastrointestinal
disorder may represent an increased risk of regurgitation and
pulmonary aspiration and will indicate a need for tracheal intubation.
The awareness about pre-existing diseases such as diabetes,
hypertension, coronary insufficiency, and hepatic or kidney
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impairments, will help determine necessary preoperative investigations,
monitoring parameters, and the choice of premedication, adjuvant and
anesthetic drugs. Furthermore, it will increase awareness of known
potential intraoperative and postoperative complications.
Past History and Prior Anesthesia
Routinely asking about prior anesthetic experiences should be an
integral part of proper preparation for anesthesia. While doing so,
patients in need of psychological help can be detected, and those at risk
for adverse effects from anesthesia, such as post-op nausea and
vomiting (PONV), allergies, or susceptibility to malignant hyperthermia
can be identified.
A prior experience of inadvertent intraoperative awareness (the
unexpected and explicit recall by patients of events that occurred during
anesthesia) should be carefully researched as this has been recognized
as a strong predictor of another similar event. The issue of inadvertent
awareness is not only relevant to the patient’s safety but also to the
standards for monitoring, as well as research in the field of neural
correlates of consciousness. The approximate incidence of awareness in
the general population is estimated to be 1-2 per 1000, while patients
with a history of intraoperative awareness with recall have an incidence
of 1 in 50.
The hypothesis of a genetic contribution is controversial. Since there is
established evidence that incidence of awareness without recall is higher
than with recall, it is safe to assume that this risk is somewhat
underestimated. Intraoperative awareness with recall can lead to posttraumatic stress disorder (PTSD). The distress experienced by the aware
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patient is particularly more intense when neuromuscular agents have
been administered.
Current Medications
A history of medication should be obtained and documented in all
patients, during the process of evaluation of general anesthesia.
Especially, in the geriatric population which consumes more systemic
medications than any other group.
Generally, administration of most drugs, with some exceptions, should
be continued up to the morning of surgery. The dosage of
antihypertensive drugs and insulin will have to be adjusted, while oral
hypoglycemic drugs should be discontinued. Diuretics, including
angiotensin converting enzyme (ACE) inhibitors, should be discontinued
the day before surgery due to their effects on water and electrolyte
balance; ACE inhibitors, which are routinely used in hypertensive
patients contribute to hemodynamic instability by interfering with the
renin-angiotensin-aldosterone system, a key player in the blood
pressure regulation. The group of monoamine oxidase inhibitors should
be interrupted 2 to 3 weeks before surgical procedure due to the risks of
interaction with anesthesia drugs. Oral contraceptives should be
discontinued at least 6 weeks before elective surgery because of the risk
of venous thrombosis.
The use of medications that potentiate bleeding needs to be carefully
evaluated taking in account the risk benefit ratio and the recommended
time frame for a discontinuation will be based on drug clearance and
half-life properties. Aspirin should be discontinued 7-10 days before
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surgery and oral anticoagulants must be stopped 4-5 days prior to
surgery. The American Society of Anesthesiologists also recommends
discontinuing herbal supplements at least 2 weeks before surgery.
Allergies
The clinical spectrum of allergic manifestations ranges from mild
reactions such as skin rash to the most severe forms with difficulty
breathing and anaphylaxis. As a first approach, preanesthetic interview
with the patient may reveal a history of allergic reaction to known
products or drugs including foods, latex, disinfectants, antibiotics and
local anesthetics. This information will be recorded in the medical file
and used to exclude exposure to the sensitizing agent, and select an
appropriate alternative.
Asthma and Chronic Rhinitis
These two pathological conditions with underlying allergic mechanisms
are the most common chronic airway diseases and as such, merit a
close evaluation when planning anesthesia in patients with these
conditions.
Two types of asthma can be distinguished. The allergic and the
nonallergic types, and although they may overlap, the allergic type is
the most frequent in children and adults. The development of asthma is
thought to be due to both genetics and environmental factors such as
tobacco smoke, air pollutants, and exposure to allergens, which may
trigger its onset.
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Allergic rhinitis is characterized by symptoms such as sneezing, nasal
blockage and itching of the nose, which can be intermittent or
permanent. More than 80% of asthmatic patients have rhinitis, and
10% to 40% of rhinitis patients have asthma. Because of this
association, patients with severe or uncontrolled rhinitis should be
evaluated for asthma before anesthesia.
Another meaningful association is sleep-disordered breathing which has
been found to be more prevalent in asthmatic individuals than in the
normal population.
Preoperative assessment and physical examination in asthmatic
patients should focus on preoperative pulmonary risk assessment. The
anesthetist should ask about exercise tolerance and clearly document
any drug sensitivities, especially aspirin given the high prevalence of
aspirin-induced asthma. The presence of decreased breath sounds,
sibilants, rhonchi, and prolonged expiratory phase, a recent
exacerbation with wheezing, cough, and dyspnea increases the risk of
perioperative pulmonary complications, in addition to an increased risk
of bronchospasm induced by tracheal intubation.
If the physical examination reveals the presence of an active
bronchospasm, elective surgery should be postponed until the patient
becomes free of wheezing, cough and dyspnea. Furthermore,
asthmatics who are smokers are strongly advised to abstain from
smoking at least 2 months before surgery.
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Preparatory Phase
The key parameters in the prevention of perioperative bronchospasm in
asthmatic patients are the control of airway inflammation and reduction
of the associated symptoms. Spirometry evaluation of the lung function
is useful. The drugs used to control asthma should be continued
perioperatively.
General Anesthesia and Associated Drugs
Drugs associated with histamine release (morphine, atracurium) should
be avoided and intubation should be performed under adequate
analgesia (fentanyl). Short-acting anesthetic agents include propofol,
and ketamine, which is a bronchodilator. Extubation will be carried out
in a sitting position and breathing oxygen.
Intraoperative bronchospasm has been reported to occur in asthmatic
patients. Based on published literature, bronchospasm induced by
irritation of the airway, occurred more frequently in patients who had
predisposing factors such as asthma, heavy smoking or bronchitis,
during induction and maintenance phase of anesthesia. Other studies
showed that an allergic mechanism was present in a significant number
of the cases experiencing bronchospasm during induction.
The treatment of bronchospasm aims at relieving as quickly as possible
the airway obstruction to reestablish normal oxygenation. For this
purpose, oxygen concentration should be increased to 100% and
manual bag ventilation started to assess the pulmonary compliance.
The concentration of the volatile anesthetic (sevoflurane or isoflurane,
but not desflurane, which is an irritant) will be increased. Propofol or
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ketamine will be added to rule out an inadequate depth of anesthesia
as a cause for the bronchospasm.
Quick acting beta 2-selective adrenergic agonists should be
administered with a nebulizer or a metered-dose inhaler to relieve the
bronchoconstriction. As an example, 8-10 puffs of salbutamol whose
onset of action is 5 minutes with a peak at 60 minutes and duration of
action extending to 4-6 hours, will be repeated at 15 to 30 min
intervals. Finally, steroids will be administered intravenously to speed
up the resolution of the airway inflammation.
Regional anesthesia is best suited for peripheral surgery in poorly
controlled asthmatic patients. In these cases, spinal technique is
considered safe.
Summary
There has been rapid growth and development of varied clinical roles
within anesthesia and surgical health teams to deliver inpatient and
outpatient treatment with the goal to improve available, cost-effective
patient care. Nurse anesthetists have a vital role in the management
of the perioperative patient as well as in the provision of clinical
support services outside the operating suite. As experienced
anesthesia clinicians, nurse anesthetists are able to assist in the
education and training of new nursing and medical staff in the
provision of varied anesthesia procedures, including pre- and postanesthesia care.
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Nurse anesthetists specifically have a vital role in the care of surgical
patients. This article provided an overview of local, regional and
general anesthesia, as well as the nurse’s responsibilities in the
management of the patient while under anesthesia. The
responsibilities of the anesthetist to deliver pre- and post-operative
care relating to the administration of anesthesia were discussed. This
includes knowledge of the side effects and contraindications of the
different anesthesia techniques, as well as an understanding of the
three phases of anesthesia: induction, maintenance and recovery.
Anesthesia care teams work in collaboration with all members of the
surgical team, as well as in other health settings to provide a plan of
care tailored to each individual patient. This plan may include
intravenous sedation, pain control, or varied types of anesthesia
during emergency, surgical or other procedures, such as palliative
types, which nurse anesthetists might be called upon to manage and
to responsibly work in concert with their health teams in the delivery
of safe and appropriate anesthesia care for patients.
Please take time to help NurseCe4Less.com course planners
evaluate the nursing knowledge needs met by completing the
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1. _____________ is used to anesthetize an area of the body.
a.
b.
c.
d.
Local anesthesia
General anesthesia
Sedation
Regional anesthesia
2. True or False: The term “asleep” is used when anesthesia
clinicians speak of a patient who is anesthetized because
general anesthesia is similar to sleep in physiological terms.
a. True
b. False
3. The triad model of anesthesia means that _______________
needed to produce all three of the intended effects of
anesthesia: narcosis, analgesia, and muscle relaxation.
a.
b.
c.
d.
sedation is
an anesthesia care team is
multiple agents are
only one agent is
4. Which of the following is characteristic of electrical brain
activity in an anesthetized subject but not an individual who
is sleeping?
a.
b.
c.
d.
Rapid eye movement (REM) sleep
Non-REM sleep
Burst suppression
Aniso-electric periods
5. Pain signals turn into perceived pain at the moment the
sensory pain signals arrive at the
a.
b.
c.
d.
thalamus.
the cortex.
nociceptors.
peripheral nerves to the spinal cord.
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6. Peripheral nerve signals that head towards the central
nervous system (CNS) are known as
a.
b.
c.
d.
efferent signals.
descending signals.
isoelectric signals.
afferent signals.
7. True or False: General anesthesia require the use of
analgesics to produce unconsciousness.
a. True
b. False
8. _____________ in the central nervous system produce
muscle movement.
a.
b.
c.
d.
Efferent signals
The dorsal columns
Afferent signals
Nociceptors
9. An individual nerve transmits its signal along the axons by a
self-propagating electrical charge called
a.
b.
c.
d.
propagation.
an action potential.
infusion.
a resting potential.
10. The succession of depolarization and repolarization allows
the propagation of the impulse to spread along _________,
in what is called action potential.
a.
b.
c.
d.
the
the
the
the
synapse
receptor
vesicle
axon
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11. The most widely known compound that interferes with
nerve conduction by blocking the voltage-gated sodium
channels is
a.
b.
c.
d.
sodium
potassium
opium
cocaine
12. True or False: Muscles relaxants are needed both for easy
access to the surgery site, and intubation.
a. True
b. False
13. The action potential is passed from neuron to neuron at the
_____________ where it triggers the release of chemicals
or neurotransmitters.
a.
b.
c.
d.
synaptic junction
dorsal columns
axon
nociceptors
14. As the action potential is passed from neuron to neuron,
another action potential mediated by the binding of the
neurotransmitter to the __________ site of the synapse
will be initiated and so on.
a.
b.
c.
d.
axon
dendritic
junction
nociceptors
15. If cocaine is present in the body, it attaches to the
dopamine, serotonin or noradrenaline transporters and
blocks the normal recycling process, resulting in a
a.
b.
c.
d.
buildup of stimulatory neurotransmitters in the synapses.
reduction of stimulatory neurotransmitters in the synapses.
reduction of the effects of stimulatory neurotransmitters.
block of the stimulant effects of cocaine.
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16. True or False: Cocaine acts as an efficient local anesthetic
agent because it blocks the voltage-gated sodium channels
in the peripheral neurons.
a. True
b. False
17. The drug procaine has a short duration of action
a.
b.
c.
d.
is efficient for topical use.
and causes minimal systemic toxicity
but creates no local irritation.
is approximately 10 times more potent than tetracaine.
18. The combination of procaine and __________ decreases its
rate of absorption in the bloodstream and doubles the
duration of its action.
a.
b.
c.
d.
sodium
potassium
ropivacaine
epinephrine
19. A 2% solution of _____________ is used topically on
mucous membranes.
a.
b.
c.
d.
ropivacaine
procaine
tetracaine
epinephrine
20. True or False: A 1%-2% solution of procaine is used for
nerve blocking in regional anesthesia and infiltration
anesthesia, and a 5%-20% is needed for spinal anesthesia.
a. True
b. False
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21. Regional anesthesia is obtained by blocking the nerve, so
that the skin, the deeper structures, and the muscles it
supplies become
a.
b.
c.
d.
slowed.
numbed.
paralyzed.
infused.
22. The regional anesthesia known as a neuraxial block
involves
a.
b.
c.
d.
upper extremities.
lower extremities.
the trunk of the body.
the spine.
23. A regional anesthesia known as ______________involves
the use of a tourniquet to isolate an intravenous injection
of anesthetic into a limb.
a.
b.
c.
d.
neuraxial block
Bier’s block
epidural block
epidural block
24. The technique of regional anesthesia involves inserting a
needle
a.
b.
c.
d.
into the nerve to deposit the anesthetic agent.
near enough to a nerve to deposit the anesthetic agent.
into the nerve, which invariably injures the nerve.
far from the nerves to protect it from injury.
25. _____________ is used to help gain accuracy and avoid
nerve and large vessels injuries during the injection of a
regional anesthesia.
a.
b.
c.
d.
A plastic catheter
A tourniquet
An ultrasound scanner
A dermatome map
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26. True or False: Pain is experienced in the subconscious part
of the brain, and triggers physiological responses,
activating the sympathetic system.
a. True
b. False
27. Regional anesthesia offers a number of advantages in
addition to pain control; for example, during surgery
regional anesthesia
a.
b.
c.
d.
vessel contraction within the anesthetized vessels.
stress-induced inflammatory response to function.
higher pressure within the dilated vessels.
allows a patient to breathe without airway support.
28. True or False: When an anesthesiologist is inserting a
needle to deposit an anesthetic agent, the anesthesiologist
may rely on a patient’s anatomical landmarks because
these do not vary from one individual to another.
a. True
b. False
29. In order to improve accuracy and speed when
administering an anesthetic agent in a patient, the
anesthesiologist finds the location for insertion of the
needle, using the help of
a.
b.
c.
d.
a plastic catheter.
an electronic nerve stimulator.
a dermatome map.
anatomical landmarks.
30. For lengthy regional anesthesia procedures,
a.
b.
c.
d.
the patient is sedated in larger doses to maintain comfort.
a Bier’s block must be used.
the patient must be unconscious.
a plastic catheter may be inserted and left in situ.
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31. To prevent a higher than intended diffusion of the
anesthetic drug in the cerebrospinal fluid (CSF), some
solutions for spinal anesthesia are formulated with
a.
b.
c.
d.
8% dextrose.
10% sodium.
epinephrine.
4% fentanyl.
32. True or False: The use of portable ultrasound scanners and
electronic nerve stimulators are used in combination by
many anesthesiologists to avoid nerve and large vessels
injuries during anesthetic drug injections.
a. True
b. False
33. Knowledge of dermatome levels is key in allowing the
anesthetist to assess
a.
b.
c.
d.
the location of the blockade.
whether to use a portable ultrasound scanner.
the level of blockade.
whether anatomical landmarks are accurate.
34. With a neuraxial block, which of the following has the
highest dermatome level?
a.
b.
c.
d.
Unmyelinated fiber level
Sensory level
Sympathetic level
Motor level
35. Spinal nerves contain
a.
b.
c.
d.
sensory pathways.
motor pathways.
autonomic fibers.
All of the above
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36. The use of neuraxial anesthesia in patients with preexisting neurologic disorders, such as multiple sclerosis
a.
b.
c.
d.
is
is
is
is
recommended as the preferred technique.
never recommended.
not recommended unless it is absolutely necessary.
recommended unless the patient refuses the procedure.
37. True or False: In general, larger unmyelinated fibers are
more susceptible to blockade than small myelinated fibers.
a. True
b. False
38. Spinal anesthesia is used for the following procedures
except for
a.
b.
c.
d.
surgeries in the head and neck.
prostate surgery.
surgeries involving the lower half of the body.
None of the above
39. _______________________ performed under spinal
anesthesia require very small incisions, produce less pain
and result in shorter hospital stays.
a.
b.
c.
d.
Laparoscopic cholecystectomy
Total joint surgery
Head and neck surgery
None of the above
40. The level and duration of spinal anesthesia are primarily
determined by three factors, including ___________,
which is the density of the drug when compared to the
density of human cerebrospinal fluid.
a.
b.
c.
d.
lordosis
hypobaricity
baricity
osmosis
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41. To optimize ____________, a pillow may be placed under
the patient’s knees or the patient may be set in the lateral
position.
a.
b.
c.
d.
postoperative pain
baricity
lordosis
osmosis
42. Sterile water or 1/2 normal saline solutions, known as
_________________, are rarely used due the osmotic
stress they might cause.
a.
b.
c.
d.
isobaric solutions
hypobaric solutions
dextrose solutions
glucose solutions
43. True or False: Opioids (usually 25 μcg fentanyl) and
morphine (0.1 – 0.5 mg) can be added to provide 24 hours
of relief, but unlike fentanyl, morphine requires in-hospital
monitoring for respiratory depression.
a. True
b. False
44. One of the three phases of general anesthesia is the
___________ phase, which is the period between the
administration of the agents and loss of consciousness.
a.
b.
c.
d.
induction
maintenance
recovery
emergence
45. __________________ tend to flow cephalad due to
negative intrathoracic pressure.
a.
b.
c.
d.
Thoracic epidurals
Neuraxial blocks
Bier’s blocks
Lumbar epidurals
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46. Neuraxial techniques are generally considered safer than
general anesthesia, particularly in patients with
a.
b.
c.
d.
with difficult airway management.
thrombocytopenia.
anticoagulation therapy.
All of the above
47. ________________ is the most frequent, immediate
adverse effect of neuraxial anesthesia, which occurs in one
third of patients.
a.
b.
c.
d.
Bradycardia
Airway obstruction
Hypotension
Hydrocephaly
48. The _______________ is usually the most stable part of
the anesthesia process.
a.
b.
c.
d.
emergence phase
induction phase
recovery phase
maintenance phase
49. True or False: If muscular blocking agents were part of the
anesthesia regimen their action should be reversed using
anticholinesterases drugs such as neostigmine.
a. True
b. False
50. _______________ induced by irritation of the airway,
occurred more frequently in patients who had predisposing
factors, such as asthma, during induction and maintenance
phase of anesthesia.
a.
b.
c.
d.
Systemic toxicity
Bronchospasm
Bradycardia
Hypertension
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CORRECT ANSWERS:
1. _____________ is used to anesthetize an area of the body.
d. Regional anesthesia
“There are three types of anesthesia to consider: 1) local
anesthesia performed typically at the site of the surgical
incision, 2) regional anesthesia is used to anesthetize an area
of the body, and it may be used alone or in combination with
general anesthesia, and 3) general anesthesia where the
patient is made completely unresponsive to pain, in which case
the patient needs assisted ventilation and close monitoring of
his or her physiological status.”
2. True or False: The term “asleep” is used when anesthesia
clinicians speak of a patient who is anesthetized because
general anesthesia is similar to sleep in physiological terms.
b. False
“Although the term asleep is used when anesthesia clinicians
speak of a patient who is anesthetized, general anesthesia is
very different from sleep in physiological terms.”
3. The triad model of anesthesia means that _______________
needed to produce all three of the intended effects of
anesthesia: narcosis, analgesia, and muscle relaxation.
c. multiple agents are
“In 1926, John Lundy introduced the term “balanced
anesthesia” to describe the use of multiple agents “sedatives”
as a premedication together with general anesthesia, to
improve the results. Later, in the 1950s Gordon Jackson Rees
and Cecil Gray proposed a triad of anesthesia consisting of
narcosis (meaning unconsciousness), analgesia, and muscle
relaxation; all represented in a triangular diagram. The triad
model means that one agent is no longer found sufficient to
produce of narcosis, analgesia, and muscle relaxation. The
triad model is still taught and used with some refinement.”
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4. Which of the following is characteristic of electrical brain
activity in an anesthetized subject but not an individual who
is sleeping?
c. Burst suppression
“Intense electrical activity occurs during the sleep cycle,
especially during the REM phase, resembling that of awake
subjects. In contrast to what happens in wakefulness and
sleep, in anesthetized subjects, the frequency of the brain
waves slows and their overall amplitude diminishes. During
general anesthesia the patient may even experience short
periods of silencing called burst suppression. Therefore, as
shown by EEG recordings, anesthesia is distinct from sleep.
Burst suppression (BS) is an electroencephalogram (EEG)
pattern that is characterized by brief bursts of spikes, sharp
waves, or slow waves of relatively high amplitude alternating
with periods of relatively flat EEG or isoelectric periods. The
pattern is usually associated with coma, severe
encephalopathy of various etiologies, or general anesthesia.”
5. Pain signals turn into perceived pain at the moment the
sensory pain signals arrive at the
b. the cortex.
“…first the detection of the painful stimulus (nociception) due
to the presence of nociceptors located in the skin and other
organs, which upon their stimulation will produce electrical
signals; in a second step the signals will be transmitted via the
peripheral nerves to the spinal cord, then to the thalamus
which is responsible for integrating sensory signals; finally the
emerging signals from the thalamus will travel to the cortex
where the pain signals turn into conscious perception, and at
this moment only, pain is being perceived.”
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6. Peripheral nerve signals that head towards the central
nervous system (CNS) are known as
d. afferent signals.
“Peripheral nerves are made of a mixture of several types of
fibers and each type has a specific function. For each particular
nerve, signals may be heading towards the CNS, known as
afferent signals (also termed ascending), or heading away from
the CNS and known as efferent signals (termed as
descending).”
7. True or False: General anesthesia require the use of
analgesics to produce unconsciousness.
b. False
“Therefore, optimal conditions for general anesthesia require a
combination of general anesthetics to produce unconsciousness
and analgesics to suppress the stress response.”
8. _____________ in the central nervous system produce
muscle movement.
a. Efferent signals
“For each particular nerve, signals may be heading towards the
CNS, known as afferent signals (also termed ascending), or
heading away from the CNS and known as efferent signals
(termed as descending)…. As for the descending signals, they
are used to produce muscle movement; they are also called
motor signals and travel via type A-fibers.”
9. An individual nerve transmits its signal along the axons by a
self-propagating electrical charge called
b. an action potential.
“An individual nerve transmits its signal along the axons by a
self-propagating electrical charge called an action potential.”
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10. The succession of depolarization and repolarization allows
the propagation of the impulse to spread along _________,
in what is called action potential.
d. the axon
“The succession of depolarization and repolarization allows the
propagation of the impulse to spread along the axon, in what is
called action potential.”
11. The most widely known compound that interferes with
nerve conduction by blocking the voltage-gated sodium
channels is
d. cocaine
“The most widely known compound that interferes with nerve
conduction by blocking the voltage-gated sodium channels is
cocaine,….”
12. True or False: Muscles relaxants are needed both for easy
access to the surgery site, and intubation.
a. True
“… muscles relaxants are needed both for easy access to the
surgery site, and intubation.”
13. The action potential is passed from neuron to neuron at the
_____________ where it triggers the release of chemicals
or neurotransmitters.
a. synaptic junction
“The action potential is passed from neuron to neuron at the
synaptic junction where it triggers the release of chemicals or
neurotransmitters.”
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14. As the action potential is passed from neuron to neuron,
another action potential mediated by the binding of the
neurotransmitter to the ________ site of the synapse will
be initiated and so on.
b. dendritic
“At this level, another action potential mediated by the binding
of the neurotransmitter to the dendritic site of the synapse will
be initiated and so on.”
15. If cocaine is present in the body, it attaches to the
dopamine, serotonin or noradrenaline transporters and
blocks the normal recycling process, resulting in a
a. buildup of stimulatory neurotransmitters in the synapses.
“Cocaine acts on the central nervous system by blocking the
reuptake of stimulatory neurotransmitters like dopamine,
serotonin and noradrenaline in the synapses. Normally,
stimulatory neurotransmitters are recycled back into the
transmitting neuron by a specialized protein transporter, i.e., a
dopamine transporter. If cocaine is present in the body, it
attaches to the dopamine, serotonin or noradrenaline
transporters and blocks the normal recycling process, resulting
in a buildup of these stimulatory neurotransmitters in the
synapses. This has the effect of enhancing their actions. It is
this second action that is responsible for both cocaine’s
stimulant and addictive properties.”
16. True or False: Cocaine acts as an efficient local anesthetic
agent because it blocks the voltage-gated sodium channels
in the peripheral neurons.
a. True
“Cocaine acts at two levels of the nervous system. Firstly, it
blocks the voltage-gated sodium channels in the peripheral
neurons making it an efficient local anesthetic agent.”
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17. The drug procaine has a short duration of action
b. and causes minimal systemic toxicity
“Procaine has a short duration of action, causes minimal
systemic toxicity and creates no local irritation. The
combination procaine-epinephrine decreases its rate of
absorption in the bloodstream and doubles the duration of its
action. A 1%-2% solution is used for nerve blocking in regional
anesthesia and infiltration anesthesia, and a 5%-20% is
needed for spinal anesthesia. Procaine is not efficient for
topical use. Tetracaine is approximately 10 times more potent
and more toxic than procaine.”
18. The combination of procaine and __________ decreases its
rate of absorption in the bloodstream and doubles the
duration of its action.
d. epinephrine
“The combination procaine-epinephrine decreases its rate of
absorption in the bloodstream and doubles the duration of its
action.”
19. A 2% solution of _____________ is used topically on
mucous membranes.
c. tetracaine
“A 2% solution of tetracaine is used topically on mucous
membranes.”
20. True or False: A 1%-2% solution of procaine is used for
nerve blocking in regional anesthesia and infiltration
anesthesia, and a 5%-20% is needed for spinal anesthesia.
a. True
“Procaine has a short duration of action, causes minimal
systemic toxicity and creates no local irritation. The
combination procaine-epinephrine decreases its rate of
absorption in the bloodstream and doubles the duration of its
action. A 1%-2% solution is used for nerve blocking in regional
anesthesia and infiltration anesthesia, and a 5%-20% is
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needed for spinal anesthesia. Procaine is not efficient for
topical use.”
21. Regional anesthesia is obtained by blocking the nerve, so
that the skin, the deeper structures, and the muscles it
supplies become
c. paralyzed.
“Regional anesthesia is obtained by blocking the nerve, so that
the skin, the deeper structures, and the muscles it supplies
become paralyzed.”
22. The regional anesthesia known as a neuraxial block
involves
d. the spine.
“There are two main categories of nerve blocks. The first called
neuraxial block involves the spine and can be subdivided in
spinal, epidural and caudal block. The second called peripheral
block may involve the eyes, breast, trunk, the upper extremity
and the lower extremity. Peripheral blocks can be used alone
or in combination with neuraxial anesthesia or general
anesthesia.”
23. A regional anesthesia known as ______________involves
the use of a tourniquet to isolate an intravenous injection
of anesthetic into a limb.
b. Bier’s block
“Another alternative technique of regional anesthesia consists
in the intravenous injection of anesthetic into a limb, which is
isolated from the circulation by a system of tourniquet and
called Bier’s block.”
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24. The technique of regional anesthesia involves inserting a
needle
b. near enough to a nerve to deposit the anesthetic agent.
“The technique of regional anesthesia involves inserting the
needle near enough to a nerve to deposit the anesthetic agent
without injuring the nerve itself. For this, it is possible to rely
on anatomical landmarks to locate the nerve, but they may
vary from one individual to another. Nowadays, the technique
is performed with the help of electronic nerve stimulators,
which are more accurate and time saving. A small electric
current is passed down the needle and, as the nerve is
approached, the current causes the muscles innervated by the
nerve to twitch, signaling to the operator that the tip of the
needle is close enough to the nerve.”
25. _____________ is used to help gain accuracy and avoid
nerve and large vessels injuries during the injection of a
regional anesthesia.
c. An ultrasound scanner
“Another way to gain in accuracy and avoid nerve and large
vessels injuries during the injection is permitted by the use of
portable ultrasound scanners, which allow a guided nerve block
under direct visualization of the neighboring structures as the
needle approaches. These two techniques complement each
other in fact, since they provide important information about
both nerve anatomy and function. Therefore, they are used in
combination by many anesthesiologists.”
26. True or False: Pain is experienced in the subconscious part
of the brain, and triggers physiological responses,
activating the sympathetic system.
a. True
“Pain is experienced in the subconscious part of the brain, and
triggers physiological responses, activating the sympathetic
system….”
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27. Regional anesthesia offers a number of advantages in
addition to pain control; for example, during surgery
regional anesthesia
d. allows a patient to breathe without airway support.
“Besides controlling pain, regional anesthesia presents a
number of advantages. It allows the patient to breathe on his
own without airway support; it reduces postoperative nausea
and vomiting; it blocks the stress-induced inflammatory
response to surgical trauma; and it avoids airway manipulation
in difficult cases. Since regional anesthesia is accompanied
with vessel dilation and lower pressure within the dilated
vessels, there will be less blood loss and less requirements for
blood transfusions. In addition, regional anesthesia allows
earlier recovery of bowel function as well as earlier
rehabilitation and hospital discharge.”
28. When an anesthesiologist is inserting a needle to deposit
an anesthetic agent, the clinician uses and may rely on a
patient’s anatomical landmarks because these do not vary
from one individual to another.
b. False
“The technique of regional anesthesia involves inserting the
needle near enough to a nerve to deposit the anesthetic agent
without injuring the nerve itself. For this, it is possible to rely
on anatomical landmarks to locate the nerve, but anatomical
landmarks may vary from one individual to another.”
29. In order to improve accuracy and speed when
administering an anesthetic agent in a patient, the
anesthesiologist finds the location for insertion of the
needle, using the help of
b. an electronic nerve stimulator.
“The technique of regional anesthesia involves inserting the
needle near enough to a nerve to deposit the anesthetic agent
without injuring the nerve itself. For this, it is possible to rely
on anatomical landmarks to locate the nerve, but they may
vary from one individual to another. Nowadays, the technique
is performed with the help of electronic nerve stimulators,
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which are more accurate and time saving. A small electric
current is passed down the needle and, as the nerve is
approached, the current causes the muscles innervated by the
nerve to twitch, signaling to the operator that the tip of the
needle is close enough to the nerve.”
30. For lengthy regional anesthesia procedures,
d. a plastic catheter may be inserted and left in situ.
“Before the regional anesthesia procedure begins, the patient
is positioned and connected to standard monitors for follow-up
of vital signs the same as if the patient were receiving a
general anesthesia. The patient is sedated in small doses to
maintain the patient’s comfort but maintain the patient’s
consciousness since the patient’s ability to communicate
throughout the surgery is important to maintain block safety.
For lengthy procedures, a plastic catheter may be inserted and
left in situ, so that repeated injections, or an infusion of
anesthetic may be given.”
31. To prevent a higher than intended diffusion of the
anesthetic drug in the cerebrospinal fluid (CSF), some
solutions for spinal anesthesia are formulated with
a. 8% dextrose.
“The height or level of the block depends on the injection site,
which is usually done in the lumbar area, but also on the
diffusion of the anesthetic solution in the cerebrospinal fluid
(CSF). To prevent a higher than intended diffusion of the
anesthetic drug, some solutions for spinal anesthesia are
formulated with 8% dextrose, making them denser than CSF
(hyperbaric solutions); after the injection, the patient will be
positioned according to gravity in order to control for the
height of the block.”
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32. True or False: The use of portable ultrasound scanners and
electronic nerve stimulators are used in combination by
many anesthesiologists to avoid nerve and large vessels
injuries during anesthetic drug injections.
a. True
“Today the nerve is located using the help of electronic nerve
stimulators, which are more accurate and save time. A small
electric current is passed down the needle and, as the nerve is
approached, the current causes the muscles innervated by the
nerve to twitch, signaling to the operator that the tip of the
needle is close enough to the nerve…. Another way to avoid
nerve and large vessels injuries during the injection is the use
of portable ultrasound scanners, which allow a guided nerve
block under direct visualization of the neighboring structures as
the needle approaches its target. These two techniques
complement each other in fact, since they provide important
information about both nerve anatomy and function. Therefore,
they are used in combination by many anesthesiologists.”
33. Knowledge of dermatome levels is key in allowing the
anesthetist to assess
c. the level of blockade.
“Knowledge of dermatome levels is key in allowing the
anesthetist to assess the level of blockade.”
34. With a neuraxial block, which of the following has the
highest dermatome level?
c. Sympathetic level
“Moreover, with a neuraxial block there is a difference between
sympathetic, sensory and motor block level. The sympathetic
level being generally two to six dermatome levels higher than
the sensory level. The sensory level is approximately two
dermatome levels higher than the motor level.”
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35. Spinal nerves contain
a.
b.
c.
d.
sensory pathways.
motor pathways.
autonomic fibers.
All of the above [correct answer]
“Spinal nerves contain both sensory and motor pathways, as
well as autonomic fibers.”
36. The use of neuraxial anesthesia in patients with preexisting neurologic disorders, such as multiple sclerosis
c. is not recommended unless it is absolutely necessary.
“The use of neuraxial anesthesia in patients with pre-existing
neurologic disorders, such as multiple sclerosis is not
recommended unless it is absolutely necessary.”
37. True or False: In general, larger unmyelinated fibers are
more susceptible to blockade than small myelinated fibers.
b. False
“In general, small myelinated fibers are more susceptible to
blockade than larger unmyelinated fibers.”
38. Spinal anesthesia is used for the following procedures
except for
a.
b.
c.
d.
surgeries in the head and neck.
prostate surgery.
surgeries involving the lower half of the body.
None of the above [correct answer]
“Spinal anesthesia is used for almost any procedure of the
lower half of the body, including orthopedics, obstetrics, and
prostate surgery. The use of spinal anesthesia has also been
described for surgeries in the head and neck where punctures
performed between the 1st and 2nd thoracic vertebrae resulted
in good analgesia.”
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39. _______________________ performed under spinal
anesthesia require very small incisions, produce less pain
and result in shorter hospital stays.
a. Laparoscopic cholecystectomy
“Laparoscopic surgeries such as laparoscopic cholecystectomy
performed under spinal anesthesia require very small incisions,
produce less pain and result in shorter hospital stays. They are
particularly advantageous to use in older and high risk patients
for general anesthesia. In the same manner, spinal anesthesia
has been associated to a lower postoperative mortality risk in
elective total joint replacement surgery.”
40. The level and duration of spinal anesthesia are primarily
determined by three factors, including ___________,
which is the density of the drug when compared to the
density of human cerebrospinal fluid.
c. baricity
“The level and duration of spinal anesthesia are primarily
determined by 1) baricity (the density of the drug as compared
to the density of human cerebrospinal fluid), 2) contour of
spinal canal, and 3) patient position in the first few minutes
after injection.”
41. To optimize ____________, a pillow may be placed under
the patient’s knees or the patient may be set in the lateral
position.
c. lordosis
“To optimize lordosis, a pillow is placed under the patient’s
knees; the other option is to place the patient in the lateral
position.”
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42. Sterile water or 1/2 normal saline solutions, known as
_________________, are rarely used due the osmotic
stress they might cause.
b. hypobaric solutions
“Isobaric solutions undergo less spread than hyperbaric
solutions; both of these solutions are suited for perineal or
lower extremity surgery. Hypobaric solutions (sterile water or
1/2 normal saline), are rarely used due the osmotic stress they
might cause.”
43. True or False: Opioids (usually 25 μcg fentanyl) and
morphine (0.1 – 0.5 mg) can be added to provide 24 hours
of relief, but unlike fentanyl, morphine requires in-hospital
monitoring for respiratory depression.
a. True
“Opioids (usually 25 μcg fentanyl) and morphine (0.1 – 0.5
mg) can be added to provide 24 hours of relief, but unlike
fentanyl, morphine requires in-hospital monitoring for
respiratory depression.”
44. One of the three phases of general anesthesia is the
___________ phase, which is the period between the
administration of the agents and loss of consciousness.
a. induction
“Induction is the period between the administration of
inductions agents and loss of consciousness where the patient
status evolves from analgesia without amnesia to analgesia
with amnesia.”
45. __________________ tend to flow cephalad due to
negative intrathoracic pressure.
d. Lumbar epidurals
“Lumbar epidurals tend to flow cephalad due to negative
intrathoracic pressure, whereas thoracic epidurals tend to stay
in place. L5/S1 anesthesia is more difficult, likely due to the
large fiber size.”
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46. Neuraxial techniques are generally considered safer than
general anesthesia, particularly in patients with
a. with difficult airway management.
“Neuraxial techniques are generally considered safer than
general anesthesia, particularly in patients with difficult airway
management, elderly debilitated patients and even the
premature newborn.”
47. ________________ is the most frequent immediate
adverse effect of neuraxial anesthesia, which occurs in one
third of patients.
c. Hypotension
“Neuraxial Anesthesia Complications: Hypotension is the most
frequent immediate adverse effect. It occurs in one third of
patients, initially due to decreased vascular resistance but in
severe cases it may be due to decreased venous return and
cardiac output. Risk factors for hypotension include arterial
hypertension, obesity, increased fetal weight, chronic alcohol
use, and a high level of blockade. Hypotension may cause
intraoperative nausea and vomiting. Bradycardia may also be
present if the block involves the heart- accelerating fibers (T1T4 level), or from a decreased venous return.”
48. The _______________ is usually the most stable part of
the anesthesia process.
d. maintenance phase
“The maintenance phase is usually the most stable part of the
anesthesia process.”
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49. True or False: If muscular blocking agents were part of the
anesthesia regimen their action should be reversed using
anticholinesterases drugs such as neostigmine.
b. False
“… if muscular blocking agents were part of the anesthesia
regimen their action should be reversed. Traditionally,
anticholinesterases drugs (neostigmine) have been used to
reverse this action. However, their efficacy has not been
consistent in resolving deep levels of neuromuscular block. A
more selective agent sugammadex is now available.”
50. _______________ induced by irritation of the airway,
occurred more frequently in patients who had predisposing
factors, such as asthma, during induction and maintenance
phase of anesthesia.
b. Bronchospasm
“Based on published literature, bronchospasm induced by
irritation of the airway, occurred more frequently in patients
who had predisposing factors, such as asthma, heavy smoking
or bronchitis, during induction and maintenance phase of
anesthesia.”
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References Section
The References below include published works and in-text citations of
published works that are intended as helpful material for your further
reading.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
O’Donnell A. (2012). Anesthesia, a very short introduction. 1st
ed. UK: Oxford University Press.
Nagrebetsky A, Gabriel RA, Dutton RP, Urman RD. (2016).
Growth of Nonoperating Room Anesthesia Care in the United
States: A
Contemporary Trends Analysis [abstract]. Anesthesia &
Analgesia.
Quintana J. (2016). Answering Today’s Need for High‐ Quality
Anesthesia Care at a Lower Cost; American Association of Nurse
Anesthetists.
Orebaud SL. (2012). Understanding Anesthesia: what you need
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