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The Art of Designing a Safe and Effective Anesthetic Protocol
Dawn Miyake, CVT, VTS Anesthesia/Analgesia
IndyVet, Indianapolis, IN
Understanding how to design an anesthetic protocol is essential for the veterinary technician.
Anesthesia is needed for a variety of veterinary procedures. Surgery, radiographs, CT, MRI, and
endoscopy also require anesthesia and/or sedation. A thorough knowledge of patient history as
well as anesthetic drugs and equipment is necessary to implement a safe anesthetic protocol.
The most obvious consideration to begin with is the species must be anesthetized. Different
species can have drastically different responses to anesthetic drugs. Feline patients are well
known to have difficulty metabolizing opioid drugs and often become dysphoric or excited with
administration. Lower doses and less frequent administration is often needed in this species
(compared to canine patients).
Even within a species, the breed of the patient can also determine the drug choices. Among dogs,
Nordic breeds (Huskies, Malamutes) are well known to be "high-strung" and often require more
sedation than some other breeds. Large breed dogs (Great Danes, Newfoundlands) frequently
require less sedation based on body weight so premedication doses are often reduced to prevent
excess sedation. Generally barbiturates, like thiopental, should be avoided in sighthounds
(Greyhounds, Whippets) since they often have prolonged recoveries.
The age of the patient must be taken into consideration as well. Neonates and pediatric patients
need to maintain their heart rate in order to maintain blood pressure and cardiac output since they
have less contractile function than adults and an immature sympathetic nervous system.
Anticholinergics are often indicated in these patients. The respiratory system may be immature
and so a higher respiratory rate is needed in order to maximize oxygenation. The liver may be
immature as well so it is important to choose drugs that do not rely heavily on hepatic
metabolism. Young patients are prone to hypothermia due to a lack of body fat and a high
surface area to body mass ratio, so it is important to be very proactive about maintaining
temperature. Hypoglycemia is common in young patients since the liver is immature and lacks
the ability to efficiently store glycogen and to convert it to glucose. Blood glucose should be
monitored in patients that are fasted for surgery and fluids with dextrose (2.5-5%) should be
administered as necessary.
Geriatric patients should maintain a heart rate as close as possible to the patient's normal range
since they can have difficulty adjusting to changes in cardiac output. As a patient gets older, the
lungs become less compliant and they have a decreased functional reserve and can become
hypoxic more quickly. Ventilation and oxygenation should be monitored and assisted as
necessary. Geriatric patients also tend to have decreased hepatic blood flow so many drugs have
an increased clearance time. Drugs that are heavily dependent on hepatic metabolism should be
avoided and drug doses may need to be decreased. Some degree of renal dysfunction is often
present as well, so maintaining blood pressure is especially important to renal perfusion. Fluid
administration is essential and administration of inotropes and/or pressors may be needed.
Physical exam
The physical exam is an essential part of any pre-anesthetic work-up. Body condition should be
noted as obese animals may need lower drug doses. Neurologic status is important in
determining the amount of sedation that is necessary. Are they BAR? Anxious? Depressed?
Doses and drug choices may need to be adjusted. Heart rate, rhythm, pulse quality and capillary
refill time can tell the examiner a lot about the patient's cardiovascular system. Is the patient
particularly bradycardic or tachycardic? Is there an arrhythmia or a murmur? If the pulse quality
is poor or the CRT is prolonged the patient may need additional stabilization before anesthesia.
Evaluation of the respiratory system can alert the anesthetist to any abnormalities that may be
worsened by the administration of sedative drugs. Is the patient febrile or hypothermic? Why?
Abnormalities in the patient's skin and hair coat can signify underlying medical conditions like
hyperthyroidism or hyperadrenocorticism. Abdominal palpation can reveal an enlarged liver or
spleen. Any of these abnormalities found on physical exam may change the anesthetic plan or
may even change whether or not the procedure goes forward.
Blood work
Pre-anesthetic blood work should never be made optional. Safe anesthesia depends on knowing
if essential body systems are working properly. The proper functioning of the liver and kidneys
is very important during anesthesia and can be determined easily by the use of routine blood
work. For young, healthy patients presenting for routine procedures a FAB 4 (PCS, TS, AZO,
BG) is usually adequate. Patients that are geriatric or have some kind of systemic disease, a
complete blood count (CBC) and blood chemistry is recommended. Depending on the patient
and the procedure, other types of blood work might be necessary such as blood type, cross
match, and/or coagulation profile.
Other pre-anesthetic tests
Some patients may require additional testing if abnormities are found on the physical exam or
blood work. Chest radiographs, abdominal radiographs or ultrasound should be performed as
indicated. Patients with cardiac disease, hyperadrenocorticism, renal disease, or sepsis should
have pre-operative blood pressure measurements. An ECG should be performed on any patient
with an arrhythmia to determine what type of arrhythmia is present or those patients with known
cardiac disease. An echocardiogram and cardiac workup is indicated with many of these patients
as well. These tests can give the anesthetist much more information so that they can make
appropriate anesthetic choices for that individual and increase the likelihood of a safe anesthesia.
Medications
A complete list of the medications that the patient is currently on should be obtained from the
owner. Many commonly used medications can affect essential body systems and may cause the
anesthetist to revise their anesthetic plan. NSAIDs and steroids can affect the liver, kidneys, and
gastrointestinal tract. If a patient is on pain medication, preoperative doses may have to be
adjusted to avoid overdose. Barbiturates and other types of anticonvulsants can cause excess
sedation when combined with other pre-anesthetic drugs and can affect liver function.
Medications for many type of cardiac disease, such as ACE inhibitors and beta- blockers will
affect the patient's heart rate, blood pressure, and cardiac output under anesthesia so it is
important to know if the patient in on these medications.
Anesthetic history
If the patient has been anesthetized before, it is helpful to review the previous anesthetic record.
This record can provide future anesthetists with a wealth of pertinent information. How did the
patients respond to the premedication chosen? What was used? If the patient responded poorly or
had some kind of undesirable reaction, that drug or drug combination can be avoided in the
future. Was it difficult to obtain an airway? What size endotracheal (ET) tube was used?
Brachycephalic breeds or even seemingly normal patients can have airway abnormalities that
may make intubation difficult or may require a much smaller or larger ET tube than is
anticipated. Having this information ahead of time allows the anesthetist to prepare for problems.
How was the anesthesia in general? Was the patient hypotensive? Were they excessively
bradycardic? Were they difficult to keep anesthetized? Was recovery rough or prolonged?
Knowing this information ahead of time can allow the anesthetist to create a plan that may
minimize the problems that were encountered previously.
Anesthetic circuit
Next, the anesthetist must decide what type of anesthetic circuit will be used. The anesthetic
circuit is important since it allows administration of oxygen and anesthetic to the patient and
removes waste gas. There are two main types of anesthetic circuits. The first is the re-breathing
circuit (circle system). As the name state, this type of circuit allows re-breathing of exhaled gases
with the carbon dioxide removed by a chemical absorbent. The advantage of this type of circuit
is that relatively low oxygen flow rates are required which minimizes heat loss and the amount of
anesthetic used. Another type of anesthetic circuit is the non-rebreathing circuit. This type of
circuit relies on a high oxygen flow rate to remove carbon dioxide. Higher oxygen flow rates
often lead to patient hypothermia so the pros and cons of this system should be balanced before
use. The main advantage of the non-rebreathing circuit is that is provides less resistance to
breathing making it more suitable for very small patients.
Airway
It is important to consider how the patient's airway will be maintained while under anesthesia. It
is recommended that patients be endotracheally intubated for long procedures or for procedures
involving the airway, oropharynx, or nasal cavity in order to protect and maintain the airway.
Patients with airway abnormalities or those with respiratory disease should be intubated as well.
Any patient who has been vomiting, regurgitating, or has been fed recently should be intubated
as well to prevent aspiration of gastric contents. Endotracheal intubation also offers the
advantage of allowing the anesthetist to provide positive pressure ventilation and minimizes
exposure of personnel to waste gases.
Maintenance of anesthesia by mask may be preferable in patients in which endotracheal
intubation may be very difficult. Guinea pigs, rats, and rabbits can be difficult to intubate and
trauma to the airway may occur during attempts. Airway trauma can lead to edema, hemorrhage
and obstruction. In many cases, maintenance by mask may be preferable in these patients,
especially for short procedures. Anesthesia with a mask is also acceptable for feline and canine
patients during short procedures in patients without respiratory disease, without airway
abnormalities, and those that do not require assistance with ventilation.
Fluid choice
The most common types of fluid used for anesthetic maintenance are crystalloid solutions.
Isotonic crystalloids are balanced electrolyte solutions and are typically run at a surgical
maintenance rate of 5-10 ml/kg/hr. Lactated Ringer's solution (LRS) is commonly used during
anesthesia. This solution contains calcium so it cannot be administered with blood products since
the calcium in this product will bind with the citrate in blood products. Normal saline (0.9%
NaCl) is a good choice for patients which have high potassium since it is potassium free. This
crystalloid is also much more acidic (pH 5.0) than most other crytalloids so may be a good
choice in patients that are alkalotic.
Colloid use is indicated for patients with a total protein (TP) less than 3.5 mg/dL. When large
amounts of crystalloids are administered to patients that are hypoproteinemic, fluid is not
retained in the intravascular space and leaks out into the interstitium resulting in edema.
Hetastarch is a synthetic colloid that can be used at up to 20 ml/kg/day. Hetastarch should be
avoided in coagulopathic patients since it can interfere with platelet adhesion. Fresh frozen
plasma (FFP) or frozen plasma (FP) is indicated for patients with low total protein as well as
coagulation abnormalities as they can provide colloid oncotic support as well as coagulation
factors.
Whole blood or packed red blood cells, should be administered to patients that are anemic going
into surgery (less than ~20% PCV), or those that are experiencing hemorrhage. It is essential to
maintain this minimum packed cell volume during anesthesia in order to maintain oxygen
delivery to tissues.
Anesthetic plan
For every anesthesia, a balanced technique is recommended. The anesthetic event consists of
four main parts: premedication, induction, maintenance, and recovery. Premedication
accomplishes several goals. First is to decrease stress in the pre-surgical patient. Anxious
patients will have high levels of circulating catecholamines which may predispose them to
cardiac arrhythmias. The second goal is to provide pre-emptive analgesia and the third goal is to
decrease the amount of induction drug needed to produce unconsciousness. Generally an opioid
and a sedative will be used. Combining these drugs produces a synergistic effect. Combining
drugs helps to decrease the amount of each drug needed and therefore decreases the incidence of
side effects. An anticholinergic may be included in the premedication for some patients
depending on the preference of the anesthetist. If more restraint is needed, a dissociative agent,
such as ketamine can be added to help facilitate patient handling and catheter placement.
Induction to anesthesia can be accomplished in variety of ways. Box inductions, mask inductions
and injectable techniques can be used. Generally, an injectable technique is preferred since the
patient is less likely to struggle and the airway can be captured quickly. Also, exposure of
personnel to waste gas is minimized. Box inductions can be used for fractious patients but are
best avoided because of the large amount of waste gas exposure, the amount of patient struggling
that can occur, and the lack of ability to capture an airway quickly. Mask inductions also present
the problem of patient struggling and waste gas exposure, but can be used if an IV catheter
cannot be placed, for short procedures, or patient's with severely impaired liver function.
Inhalant agents are commonly used for maintenance, especially in longer procedures. Isoflurane
and sevoflurane are the most popular inhalants. Both of these have comparable cardiovascular
and respiratory effects but sevoflurane provides a slightly more rapid induction and recovery.
Performing a local block prior to surgery can help in the maintenance phase by significantly
decreasing the amount of inhalant anesthetic needed to provide a surgical plan of anesthesia.
Whenever possible, a local block should be considered as part of the anesthetic protocol. Many
patients will also benefit from addition of a constant rate infusion (CRI) of an analgesic drug
during their anesthesia. Besides providing additional analgesia for painful procedures, a CRI can
be used to reduce inhalant requirements and minimize the cardiovascular effects of the inhalant.
This can be particularly desirable in patients with cardiovascular compromise, septic shock, or
other systemic disease.
Propofol can also be used as a CRI for maintenance of anesthesia. This would be indicated in
patients with severe intracranial disease since propofol decreases cerebral blood flow and
intracranial pressure (unlike most inhalant anesthetics). Opioid CRI's (fentanyl, remifentanil) can
be used for maintenance of anesthesia without the addition of inhalant in patients who cannot
tolerate the cardiovascular effects of inhalants. Total IV anesthesia with an opioid often requires
a high rate of administration which often results in hypoventilation. Positive pressure ventilation
is commonly needed and end tidal carbon dioxide levels should be monitored.
Recovery
The recovery phase of anesthesia involves the transition from unconsciousness back to
consciousness. Priorities during this phase include ensuring that spontaneous ventilation is
adequate, that the patient can maintain their airway, and that dysphoria, anxiety, and pain are
minimized. Hypoventilation while under anesthesia is common. After anesthesia is discontinued,
it is important to make sure that oxygen is provided and ventilation is assisted until the patient is
able to ventilate themselves adequately. Extubation should occur once the patient is awake
enough to maintain their airway on their own. Primarily the patient's swallowing reflex should
have returned and the patient should be able to lift their head unassisted. Patients with airway
abnormalities or undergoing procedures involving the nose, mouth, airway or neck should
remain intubated as long as they will tolerate the ET tube since they are at higher risk of airway
swelling, obstruction, or aspiration of blood.
Dysphoria and pain can be minimized post-operatively by pre-emptive administration of
analgesics and sedatives. Ideally, this will start with an adequate premedication protocol and end
with a plan for the recovery. A plan for post operative analgesia should be in place whether it
involves an NSAID, local analgesia/anesthesia, opioid bolus dosing or a CRI. Planning ahead
makes it much more likely to have a successful and safe outcome to an anesthetic event.
Perioperative Pain Management
Systemic Analgesics and Local Anesthetics
Dawn Miyake, CVT, VTS Anesthesia/Analgesia
Indyvet, Indianapolis, IN
Pre-emptive and multimodal use of analgesics in the perioperative period is becoming
increasingly common in veterinary practice. Awareness of the complexity of the pain pathways
and the potential for interaction among those pathways has also increased. Improved comfort
with the use of continuous rate infusions, opioids, local anesthetics, NSAIDs, NMDA receptor
antagonists and alpha-2 agonists. By combining analgesics targeting different portions of the
nociceptive pathway (multi-modal analgesia), the net analgesic effect is synergistic, allowing for
decreased doses and side effects.
Opioids
Opioids are a diverse group of agents that produce analgesia by their actions on specific
opioid receptors (mu, kappa, and delta). These receptors vary in their pharmacological effects
and their distribution throughout the body. Pure opioid agonists, including morphine,
oxymorphone, hydromorphone and fentanyl bind to all of these receptors and provide the
most profound analgesia.
Pure opioid agonists are frequently used as continuous rate infusions during the
anesthetic period. At lower doses, these infusions may be continued into the post-operative
period and provide continued analgesia while minimizing respiratory depression.
Opioid administration can produce clinically significant side effects, including sedation,
dysphoria or excitement, respiratory depression, vomiting and decreased GI motility. Therefore,
opioid agonist-antagonists and partial agonists (butorphanol, buprenorphine) may be preferred
in some cases. These drugs generally provide less analgesia than pure opioid agonists, but the
side effects also tend to be less severe. Butorphanol, a kappa agonist and mu antagonists, is
generally considered a mild to moderate relatively short lived analgesic. Buprenorphine, a
partial mu agonist, provides effective analgesia for many types of procedures and has a
relatively long duration of action.
NSAIDs
New information and the availability of new drugs have changed the way that NSAIDs
are viewed as part of the multimodal approach to pain management. While inhibition of
peripheral COX activity and the resulting anti-inflammatory effect is part of the mechanism by
which NSAIDs provided analgesia, it is now recognized that much of their analgesic effect is due
to inhibition of COX activity, more specifically COX-2 activity, centrally. It may take up to two
hours to achieve effective inhibitory levels within the dorsal horn of the spinal cord and this
should be taken into account preoperatively, when measuring the risk/benefit ratio of using
these drugs at a time when anesthetic agents may adversely affect blood pressure and or renal
blood flow and oxygen delivery.
When selecting a NSAID for perioperative use, decisions should be made based on both
safety and efficacy. In addition, thought should be given to the physical status f the patient,
procedure to be performed, and anesthetic agents being used. If preemptive analgesia is the
goal, additional analgesics from other drug classes such as the opioids may be used and may be
preferred in many instances. Avoid NSAIDs in patients which are hypovolemic, hypotensive or
with underlying renal, hepatic or GI disease.
Local Anesthetics
Lidocaine and bupivacaine are local amide anesthetics and act by blocking the sodium
channel in the nerve membrane, inhibiting action potential generation and transmission of the
nociceptive signal. Both lidocaine and bupivacaine may be used for local injection at the nerve.
These agents can be used for brachial plexus blockade in patients undergoing forelimb
procedures. They can be given epidurally. Indications for epidurals include intraoperative
management of high-risk patients, perioperative analgesia, cesarean section, caudal
anesthesia/analgesia perineum, hind limbs, and abdomen and depending on the agent chosen,
thoracotomy. Successful epidurals may reduce gas inhalant as well as post operative pain
medication requirements. Contraindications to epidural anesthesia include infection at the site
of needle placement, inflammatory CNS disease, and presence of a coagulopathy or sepsis.
When used epidurally, the site for injection is usually the lumbosacral space. A combination of
morphine with bupivacaine is recommended to take advantage of the synergistic effect of using
analgesic agents from two different classes. With this combination, the bupivacaine works
within the first 30 minutes and lasts about 8 hours, while the morphine’s peak effect occurs
about 4-8 hours after administration and lasts 24 hours. Oxymorphone and fentanyl are
effective when given epidurally but these drugs are highly lipid-soluble and rapidly diffuse out
of the epidural space, giving a relatively short analgesic effect. Lidocaine may be given as a low
dose infusion to enhance the effect of other analgesic drugs. It is frequently used in
combination with either morphine or fentanyl given as a CRI +/- ketamine. CRIs of lidocaine
should be used cautiously, if at all, in cats due to pharmacokinetics which are very different
from the dog, leading to relatively high peak levels even at low doses. Bupivacaine should never
be given intravenously in any species.
Care must be taken when using local anesthetics drugs by any route, due to their
relatively high systemic toxicity. Toxic cardiovascular and neurologic effects may be seen at
doses relatively close to the effective dose. These agents rely on hepatic metabolism; therefore,
adjustments should be made in patients with liver disease. Half-lives are longer in cats and toxic
doses are lower than for dogs. There are no available reversal agents.
NMDA Antagonists
While traditionally considered a dissociative anesthetic, ketamine is also recognized as
an NMDA receptor antagonist. The NMDA receptor appears to play a central role in the
development of central hyper sensitization and “wind up” of the dorsal horn neurons. Given as
a low dose infusion, ketamine may be used as an adjunct to other analgesic therapy such as
continuous rate infusion morphine or fentanyl without causing anesthesia or pronounced
sedation. Amantadine is an oral NMDA receptor antagonist which has been recommended to
help decrease wind up in patients with chronic pain.
Alpha-2 Agonists
Dexmedetomidine is not a first line analgesic gent, but excellent as an analgesic
adjuncts. It causes sedation, muscle relaxation and anxiolysis. The hemodynamic effects have
typically been described as a biphasic blood pressure response with decreased heart rate, and
increased systemic vascular resistance and central venous pressure. The initial increase in blood
pressure results from peripheral vasoconstriction, seen as peripheral blanching and “muddy”
oral mucous membranes. This is associated with increased vagal tone and decreased heart rate.
Blood pressure then falls as vasoconstriction decreases and a central hypotensive effect
predominates.
Monitoring the Anesthetized Patient
Dawn Miyake, CVT, VTS Anesthesia / Analgesia
IndyVet, Indianapolis, IN
Anesthesia may compromise the patient's homeostasis at any time during the
anesthetic period and in many ways, all of which are not predictable. Also, anesthetic
emergencies tend to be rapid in onset and devastating crises and help the anesthetist to
maximize patient safety and minimize adverse effects of anesthesia on the organ systems.
Monitoring improves our odds of having an uneventful anesthetic period and recovery.
Because anesthesia can cause Central Nervous System, cardiovascular, and respiratory
depression, it makes sense that we would want to monitor all of these systems in some way.
The American Society of Anesthesiologists (ASA) Standards for basic anesthesia monitoring call
for qualified anesthesia personnel to be present in the room throughout the conduct of all
general anesthetics, regional anesthetics, standing anesthetics, and monitored anesthesia care.
Further, during all anesthetics, the patient's oxygenation, ventilation, circulation and
temperature should be continually evaluated. To this end they require oxygenation to me
monitored by inspired gas analysis and blood oxygenation (pulse oximetry, blood gases).
Ventilation monitored by clinical signs and capnography (expired gas analysis). Circulation
should be monitored by ECG, heart rate, blood pressure, palpation of pulse and/or Doppler
ultrasonic flow detector. Temperature is another parameter that they require to be monitored.
In the veterinary patient, the priorities for monitoring begin with depth of anesthesia in
a "hands on" fashion. A dedicated person monitoring important parameters through
continuous data collection and interpretation. These parameters include heart rate, heart
rhythm, blood pressure, oxygenation (O2 saturation), ventilation (pO2, pCO2) and temperature.
It is recommended that a continuous written record is to be maintained from the premedication period through the recovery period. This record should contain detailed patient
information to include owner's last name, patient's name, clinic identification number, age,
species, breed and color description. An account of the drugs and dosages and time of
administration to the patient should be documented. Dosages should be given in mgs not mls.
A running record of vital signs should be kept. Minimally this should include heart rate,
respiration rate and systolic blood pressure. Additionally, diastolic and mean arterial pressure,
CO2concentration and temperature should be monitored and recorded if these parameters are
available to the anesthetist.
It is recommended for the use of continuous monitors. Their advantages are numerous.
The most obvious advantage is that they allow for the monitoring anesthetist better access to
information as they can be used to detect acute changes, make rapid interpretation of data and
effect a response quickly and immediately. It also allows for good monitoring in the event of
limited manpower in the clinic. In small animal anesthesia the most cost effective continuous
monitor would, in my estimation , be the Doppler.
After temperature, pulse and respiration measurement that you can do by "hand", the
first parameter to measure would be blood pressure. Under anesthesia you want to maintain,
minimally in small animal patient, a systolic pressure (SAP) of 100 mmHg, diastolic (DAP) of 50
mmHg and a mean (MAP) of 70 mmHg. Blood pressure can be measured using either a direct or
indirect method. The direct method requires the insertion of a catheter into the artery of the
patient and attaching it to an anaeroid manometer or blood pressure transducer. Direct blood
pressure monitoring is continuous. This requires practice as arterial catheter placement can be
challenging. This method also requires that the anesthetist maintain a patent catheter. The
indirect measurement of blood pressure can be achieved with the use of a Doppler flow
detector or an oscillometric cuff monitor.
Patient oxygenation is another parameter that should be monitored. This can be
accomplished with the use of a pulse oximeter. Pulse oximetry is an estimate of arterial oxygen
status determined by the measurement of the degree of oxygen being carried by hemoglobin. It
is reported as a percent. The pulse oximeter also measures heart rate. It is a continuous
measurement and most oximeters have an audible heart rate detector and alarm. The accuracy
of the pulse oximeter can be influenced by positioning and vasodilation or vasoconstriction. In
general, an SpO2 reading of 90% indicates a PaO2=60mmHg and an SpO2 of 99% indicates an
SpO2> 100mmHg. Pulse oximetry is a beneficial measurement in the face of pulmonary disease,
airway disease or in situation where desaturation is an expected event. The pulse oximeter is
not a respiratory or ventilation monitor.
Ventilation is also a very important measurement to monitor. To assess ventilation, you must
monitor pO2 and pCO2 levels. Carbon dioxide is a byproduct of metabolism that is removed
from the body through the respiratory system. If the patient has a normal metabolism, the
measured levels of CO2 are a direct indication of the efficacy of his/her ventilation status.
Carbon dioxide can, at high levels, be anesthetic to the patient. It can also stimulate a stress
response that includes epinephrine release, arrhythmias and tachycardia. Prolonged elevation
of CO2 levels can cause damage to the nephrons. This damage does not become clinical until
65% of the total nephrons are destroyed. A poorly ventilated patient could have CO 2 caused
nephron damage that contributes to renal disease and failure at a later time. A patient on 100%
O2 should have a pO2 measurement of 400-500 mmHg.
The two ways in which to monitor ventilation are blood gas analysis and capnography. Blood
gas analysis is the "gold standard" for measuring the exact amount of carbon dioxide and
oxygen in the arterial blood of a patient. It can be used for accurate assessment of adequacy of
both ventilation and oxygenation. A heparinized blood sample is collected anaerobically from
an artery and introduced into a blood gas analyzer that measures pH, PaO2 and PaCO2 with
electrodes and calculates bicarbonate and base excess/deficit. Metabolic acidosis indicates
inadequate tissue perfusion and oxygen delivery. Metabolic acid means increased acid
production or decreased acid excretion. Respiratory acidosis indicates inadequate ventilation.
Capnography measures the end-tidal CO2 (ETCO2) by taking a sample of exhaled gas
from the endotracheal tube in intubated patients. By sampling gas at the end of the expiratory
phase, the sample will be alveolar gas or end-tidal gas rather than dead space or non-perfused
gas. ETCO2 is a fairly accurate estimation of arterial carbon dioxide. Capnography can be a good
estimation of PaCO2 and adequacy of ventilation in endotracheally intubated patients but can
be difficult and inaccurate in awake patients. It is also inaccurate in patients with significant
ventilation-perfusion (V-Q) mismatch. The equipment necessary for capnography is expensive
but has an added parameter that is very helpful to the anesthetist. The capnograph also
measures inspired and expired (end tidal) inhalant levels.
It is important to monitor the cardiovascular system as well as the respiratory system.
Heart rate is the most obvious parameter associated with this system. Heart rate can be
monitored by palpation of peripheral pulse, use of a stethoscope, or ECG, a pulse oximeter, or
Doppler blood pressure monitor. Pulse pressure is the difference between systolic and diastolic
pressures. If the heart rate you obtain is different from the rate you determine by auscultation
then there is a pulse deficit and ECG should be performed to rule out an arrhythmia. Mucous
membrane color is another indicator of patient condition. Gum color as opposed to tongue
color should be evaluated. Pink is an indication of good perfusion and oxygenation; pale, gray
or white are usually caused by vasoconstriction, significant hypotension or cardiac arrest. Bright
red is present in the face of endotoxic or septic shock whereas bright pink is indicative of
hypercarbia. Capillary refill time should be about 1 second but will be prolonged by low blood
pressure and/or cardiac output as well as vasoconstriction.
Body temperature should be monitored in all anesthetized patients. Hypothermia can
be an indication of poor cardiac output and poor tissue perfusion. Harmful effects of extended
periods of hypothermia can include cardiac dysrhythmias, bradycardia, platelet dysfunction and
coagulopathies, altered mental status, impaired renal function, decreased drug metabolism and
reduced MAC. Poor would healing and increased chance of postoperative infections are serious
adverse side effects of hypothermia. Hypothermia can be treated with circulating warm water
blankets, Bair Hugger forced air heating blankets, blankets and or fluid warmers.
The goal of patient monitoring is early detection of an adverse response to anesthesia.
Patient monitoring aids the anesthetist in being proactive in the response and treatment of
adverse effects of the anesthetic period. The anesthetist should use monitoring to determine
when and how to minimize the intensity and duration of stressors the patients face.