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UCHSC Neuroanesthesia Handbook For Residents
INTRODUCTION
Welcome to Neuroanesthesia. We hope this month is an interesting and educational
experience. This guide is for anesthesia residents as they prepare for anesthesia in
neurosurgical patients. It outlines the curriculum for learning and allows a quick
familiarization with some of the special considerations that apply to neurosurgical cases.
These guides should not be used as a replacement for background reading, discussion
with the anesthesia faculty and consultation with the surgeons, but should be helpful to
supplement these.
During this 2 month long rotation, we recommend you follow the curriculum developed
by the Society of Neurosurgical Anesthesia and Critical Care (SNACC). These are
attached and under continual development. To accomplish these goals, residents will
be asked to do the following:
1.
Prior to the rotation: be familiar with the content of this introductory manual
Neuroanesthesia Reading List
The suggested readings below indicate the minimum reading expectations for two months of
neuroanesthesia, which typically will comprise one month in the CA2 year and one month in the
CA3 year. Additional reading is encouraged as well, and the faculty will be happy to make
recommendations. Reading noted as “Miller” refers to Miller’s Anesthesia, Seventh Edition, RD
Miller, editor, Elsevier, Philadelphia, 2009 or the electronic version that is available on-line
through the Health Sciences Library under MDConsult. “Mongan” refers to Mongan PD, Sloan
TB, Soriano S eds. A Practical Approach to Neuroanesthesia, Wolters Kluwer, 2013. The
reading assignments in Miller intentionally contain fewer pages than those in Mongan, because
each page contains more words. The Mongan book and the resident handbook will be provided
by the department prior to the rotation through the residency coordinator.
REQUIRED READING:
In order to facilitate a coordination of reading topics and discussion between residents
and assigned staff the following chapters in Mongan will be assigned on a daily and
weekly basis. Not every rotation will start on a Monday. Thus, the reading assignments
will begin on the first day of the first week of the rotation according to the in the following
table. For example if your rotation starts on a Thursday you will be responsible for
Chapter 4 Routine Craniotomy. The other chapters will be covered in the fourth week of
the rotation.
Mongan Chapter
1 (Brain Metabolism and CBF)
2 (Anesthesia effects on CBF)
3 (Fluid Management)
4 (Routine Craniotomy)
5 (Emergency Craniotomy)
6 (Posterior Fossa)
8 (Pituitary Gland)
9 (Intracranial aneurysms)
10 (AVMs)
12 (Spinal cord injury)
13 (Intramedullary Spinal Cord Tumors)
14 (Functional Neurosurgery)
23 (Stroke and Brain Protection)
26 (Electrophysiology)
27 (ICP)
29 (TBI)
Week
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
Day
Monday
Tuesday
Wednesday
Thursday
Monday
Tuesday
Wednesday
Thursday
Monday
Tuesday
Wednesday
Thursday
Monday
Tuesday
Wednesday
Thursday
RECOMMENDED READING:
Week 1.
Cerebral Physiology, Ch 13 Anesthesia, 7th edition, Ronald Miller Ed.
Churchill Livingston, 2009
Week 2.
Neurological Monitoring, Ch 46 Anesthesia, 7th edition, Ronald Miller Ed.
Churchill Livingston, 2009
Week 3/4.
Neurosurgical Anesthesia, Ch 63 Anesthesia, 7th edition, Ronald Miller
Ed. Churchill Livingston, 2009
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Table of Contents
Introduction..............................................................................................................page 1
Curriculum .............................................................................................................page 4
Reading Material and References .........................................................................page 5
General Considerations .........................................................................................page 6
Emergency Craniotomy .........................................................................................page 8
Routine Craniotomy .............................................................................................page 11
Posterior Fossa/Tumor Surgery ...........................................................................page 15
Sitting Position
Air Embolism
Transphenoidal Pituitary Resection .....................................................................page 20
Carotid Endarterectomy (CEA) ............................................................................page 21
Intracranial Vascular Surgery ...............................................................................page 24
Spine Surgery ......................................................................................................page 29
Parkinson’s Disease………………........................................................................page 33
Awake Craniotomy (for Excision of Seizure Foci) .................................................page 36
Neurophysiologic Monitoring ...............................................................................page 39
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Society of Neurosurgical Anesthesia and Critical Care Anesthesia Residency
Curriculum
Goals
A.
B.
C.
D.
E.
F.
Administer anesthesia safely to patients with neurologic disease
who are undergoing neurologic or non-neurologic surgery,
diagnostic procedures requiring anesthesia, or non-surgical
interventions requiring anesthesia.
Demonstrate knowledge of concepts of central nervous system (CNS)
physiology and anatomy as they relate to neuroanesthesia.
Know the effect(s) of commonly used anesthetic agents and adjuvant
agents. For example, opiates, isoflurane, and antihypertensitives, on
patients with normal cerebral physiology as well as on patents with
significant pathology such as brain tumor or subarachnoid hemorrhage.
Be aware of the anesthetic implications of the most common
neurosurgical procedures, that is what is likely to happen during
neurosurgery that will affect anesthetic management.
Know basic generators of the electroencephalogram, evoked
potentials, and electromyogram as well as the significance of
intraoperative changes.
Understand how concurrent non-neurological medical illnesses affect
anesthesia during neurologic surgery.
Evaluation to Determine Goal Achievement


1.
2.
3.
4.
Preoperative discussion with the attending physician
Attending evaluation of daily clinical performance in the operating room in the
following areas:
Preparation for case and ability to carry out plan discussed the night before
Recognition of intraoperative problems and communication with the attending; ability
to appropriately respond to changing clinical situation; clinical judgement
Technical skills of placing lines and positioning the patient
Application of basic and clinical science knowledge and skills to the neurosurgical
patient.
 Educational feedback, using an appropriate setting and a supportive critiquing
approach, is provided by the attending anesthesiologist
 At the conclusion of each neuroanesthesia rotation an overall performance
evaluation is made based an the above criteria.
 Performance on the In-Training Examination for the American Board of
Anesthesiologists (ABA) and/or departmentally held in-training examinations. The
training staff review results from these sources and may adjust the curriculum
accordingly.
 Resources available to accomplish goals include but not limited to:
Page | 4
A.
Neuroanesthesia grand rounds
B.
Human patient simulation
C.
Library resources (books, electronic textbooks, videotapes, network access,
Internet)
D.
Core lecture program/case conferences
E.
Problem-based learning program
F.
Mock oral examinations
Reference Reading Material (Chapters and Books)
Recommended Reading - Prior to the Rotation
UCH Neuro Manual
2. Required Reading - During the Rotation
Chapter 13: Patel PM, Drummond JC, Cerebral physiology and the effects of
anesthetics and techniques, Miller, pp 305-340 (32 pages of text).
Chapter 46: Seubert CN, Mahla ME. Neurologic monitoring, Miller, pp 1477-1514 (34
pages of text).
Chapter 53: Drummond JC, Patel PM, Neurosurgical anesthesia, Miller, pp 2045-2088
(38 pages of text).
Second Month of Neuroanesthesia (Mongan)
Chapter 5
(Emergency Craniotomy)
Chapter 7
(Carotid Endarterectomy)
Chapter 11 (Neurosurgical Procedures and Chronic Pain)
Chapter 24 (Anesthetic-induced Neurotoxicity)
Chapter 25 (Neurosurgery in the Pregnant Patient)
Chapter 28 (Other Monitoring Techniques)
Chapter 30 (intensive Care of Spinal Cord Injury)
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GENERAL CONSIDERATIONS
Objectives:
A.
B.
C.
Review the medical history and physical examination of patients; define
the type and severity of their major neurosurgical problem(s) as well as
other medical problems that may affect anesthetic care; and know what
information about nervous system function and pathology is important to
the anesthesiologist.
Recognize both the adult and pediatric patient with poor elastance or
increased intracranial pressure (ICP) (signs and symptoms).
Specifically, the resident should exhibit mastery of the following concepts:
 autoregulation of cerebral blood flow.
 cerebral blood flow in response to CO2




D.
blood flow relationship to cerebral oxygen (CMR0 ) and glucose
(CMRglu) metabolic rates
cerebrospinal fluid physiology (formation, reabsorption, flow, and
role in compensation for an intracranial mass); blood brain barrier
composition and function
pathophysiology of ischemic brain injury (assists in understanding
strategies for cerebral and spinal cord protection)
basic neuroanatomy (facilitates understanding of discussions with
surgical colleagues about the proposed surgical procedure)
including: blood supply to brain and spinal cord, organization of
motor and sensory tracts in the brain and spinal cord, and
ventricular system and normal flow of CSF
2
Know the effects of anesthetic and adjuvant drugs on autoregulation of cerebral
blood flow, cerebral blood flow response to CO2, cerebral metabolism and its
relationship to cerebral blood flow, and cerebrospinal fluid
production/reabsorption. Important drug classes:
 Hypnotic agents including barbiturates, benzodiazepines.
etomidate, and propofol
 Ketamine
 Nitrous oxide
 Potent inhalation agents (emphasize differences among these
agents)
 Opiates and antagonists
 Muscle relaxants - both depolarizing and nondepolarizing
Understand the indications, required techniques, and implications of the
following special procedures sometimes used during neuroanesthesia: be
aware of impact of each of these techniques on postoperative care of the
patient.
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1.
2.
3.
4.
a.
Induced hypotension
Induced hypertension
Moderate hypothermia
Pharmacologic cerebral protection
Use an understanding of the pathophysiology of cerebral ischemia to understand
the rationale for currently used methods for cerebral protection.
b. Be knowledgeable of current literature regarding effectiveness of pharmacologic
cerebral protection.
c. Be aware of those pharmacologic techniques that have been demonstrated not
to be effective.
In general, the complexity of neurosurgical cases can vary widely between
procedure and for each patient. Anesthesia plays an integral role in many of
these procedures since the type of anesthetic, method of delivery and
adjunctive management techniques can enormously influence the ability of the
neurosurgeon to effectively conduct the procedure. Hence, planning of the
anesthetic becomes extremely important.
First, consultation with the neurosurgeon preoperatively is very important. Small
changes in the type and location of pathology can make major changes in their
approach (e.g. position). Identifying how and in what position they will conduct
the surgery is critical in planning the anesthetic. Secondly, it is important to ask
about special intraoperative needs and monitoring (such as awake intubation,
awake craniotomies, need for EMG monitoring, etc). Finally, a discussion should
be made about postoperative plans and expectations so that a long term
anesthetic plan can be made for the patient.
Prior to the surgery, the anesthesia team (resident-attending) should also plan
their approach taking into account the above needs and the interaction of
anesthetics. This should generally be done the night before and reviewed in the
morning with any last minute changes.
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EMERGENCY CRANIOTOMY
Objectives:
Understand the indications for emergency craniotomy (usually as a result of
traumatic brain injury):

Acute CNS physiology changes with intracranial hemorrhage

The natural history of intracranial hemorrhage, specifically regarding
advantages of early versus delayed surgery

Know potential effects of intracranial hemorrhage on the function of other
systems including the cardiovascular system, pulmonary system and renal
system

Evaluate the neurologic status of the patients: C-spine, orientation,
motor/sensory function and patients with subarachnoid hemorrhage and
intracranial aneurysm by means of the Hunt-Hess grading system
Head injury: Know the pathophysiology and anesthetic implications of the following
types of head injury:

Acute epidural hematoma

Acute subdural hematoma

Intracerebral hematoma

Chronic subdural hematoma

Diffuse axonal injury
The patient presenting for emergency craniotomy must be assumed to have both a
full stomach and have raised ICP (which can delay gastric emptying).
Oxygen should be applied early, the head should be raised if possible and ensure that
the blood pressure is adequate. A brief neurologic exam should rapidly be done to
document major deficits. With trauma, the status of the cervical spine needs to be
clarified as neck injury is common (10-20%) with head injury and it is important to know
if a basilar skull fracture is present. Unfortunately 30% of unstable spines are missed by
lateral cervical spine films so it may be prudent to consider the spine unstable with head
and neck trauma (hence, use in-line stabilization during intubation).
Page | 8
Monitoring should be applied and ventilation assisted if necessary (avoid hypercarbia).
An oral citrate preparation should be given if the patient is awake and cooperative. If the
neck is not injured, induction is generally achieved with thiopental, propofol or
etomidate, with some narcotic (fentanyl) and succinylcholine. If succinylcholine is not
contraindicated, pretreatment with a nondepolarizing muscle blocker will prevent the
ICP from increasing markedly as is typically seen with administering only
succinylcholine. On induction, cricoid pressure should be used and ventilation
supported if it is possible to do so without generating excessive pressure likely to place
air in the stomach. Lidocaine (1-1.5 mg/kg) is often a useful adjunct to induction and
intubation. The induction drug and dosage must be chosen based on cardiovascular
stability, but lidocaine, some narcotic and sedative are almost always suitable. Alternate
airway techniques should be used if neck or face trauma contraindicates direct
laryngoscopy. A basilar skull fracture (suggested by intracranial air or CSF rhinorrhea)
contraindicates the nasal route for intubation and NG tube placement.
Immediate methods to reduce ICP should be used in consultation with the
neurosurgeon. Hyperventilation may not be appropriate with acute head trauma as
reductions in cerebral blood flow may be deleterious. A reasonable anesthetic technique
would involve a narcotic (fentanyl), muscle relaxant, air/oxygen. Low dose isoflurane (as
tolerated) may be appropriate if brain swelling is not excessive. With very high ICP it is
probably best to avoid nitrous oxide, ketamine or inhalational agents and only use an
intravenous technique (TIVA). If intracranial air is seen on the CT, nitrous oxide must
not be used. Drugs which cannot be reversed should be avoided in all but small doses
as they may confuse the postoperative mental status. Fluid management is critical and
if blood loss is moderate then replace with blood or colloid (preferably albumin) if
needed. Hetastarch has an associated coagulopathy at higher doses so it is usually
avoided.
Maintenance of adequate blood pressure is of paramount importance. If hypotension
occurs, consider extracranial blood loss (e.g. long bone fractures, hidden abdominal
bleeding, or intrathoracic/cardiac causes); hypotension is not common from intracranial
injury (except with severe, lethal, injury to the pons).
Although an awake patient is desirable for evaluation of the post operative neurologic
status, patients who were comatose or barely responsive preoperatively will likely be
difficult to awaken and may best be taken to the ICU intubated and ventilated. Early
consultation with the neurosurgeon about reasonable expectations for awakening and
post operative plans should be made. In some cases, postoperative intubation is helpful
for hyperventilation and protection of the airway. Further, severe head trauma may
have accompanying pulmonary dysfunction (e.g. neurogenic pulmonary edema)
necessitating aggressive pulmonary management.
Patients with severe head trauma (particularly involving tissue destruction) may
develop DIC. Check DIC profile if suspicious. Review ECG for ischemia as this may
appear as subendocardial ischemia which is rarely associated with myocardial
Page | 9
dysfunction unless cardiac injury or infarction has occurred. However, when present it
is usually a sign of severe intracranial problem.
Consultation with the intensive care unit team (including nurses) will be helpful to
make a smooth transition to ICU.
Page | 10
ROUTINE CRANIOTOMY
Objectives:
There are several indications for craniotomy which include tumor resection,
seizure foci resection, hydrocephalus, vascular abnormalities. This section
focuses on indications that result in elevated ICP.
Understand the different presentations of a patient with hydrocephalus and
choose an appropriate anesthetic regimen.
Know the differential diagnoses and treatment alternatives of intraoperative
intracranial hypertension (“tight brain”).
Understand the role of fluid management during neurosurgical procedures but
especially in patients with high ICP.
 importance of volume of IV fluid infused versus osmolality of the plasma
 osmolality of commonly used IV fluids including normal saline solution,
plasmalyte, lactated Ringer’s solution, hydroxyethylstarch, protein solutions
(e.g. 5% and 25% albumin)
 Current concepts regarding use of colloid versus crystalloid solutions
 Mechanism of action and appropriate use of mannitol solutions during
neurosurgical procedures
 Appropriate use of non-osmotic diuretics during neurosurgery
 Appropriate use of glucose containing solutions during neurosurgery and
current concepts regarding effects of glucose on outcome following CNS
ischemia
Know the basic differences between the following types of brain tumors; know
the implications of size, speed of growth, vascularity, surrounding edema
 Infratentorial -e.g. cerebellar astrocytoma or acoustic neuroma
 Supratentorial - e.g. meningioma, glioblastoma
 Pituitary tumors
Preoperatively, several considerations must be identified: 1) the location of the
tumor/mass and 2) the surgical approach, notably the position required. Preoperative
neurologic symptoms should be documented in the chart. In patients who have some
level of altered mental status, premedication should generally be light (if at all). Drugs
which depress respirations (eg. narcotics), thereby raising ICP or those that might
further worsen mental status (thus causing a preoperative change in consciousness)
should be used cautiously, if at all. Preoperative anti-seizure drugs and steroids (e.g.
decadron) should generally be given if routinely taken by the patient. Stress dose
steroids are not needed as decadron will likely be continued. Confer with neurosurgical
team prior to administration.
Induction: When ICP may be elevated (intracranial pathology), induction should be
Page | 11
o
accomplished by means to keep ICP low, 1) raising the head of bed 10-20 , 2)
preoxygenation, 3) voluntary hyperventilation (if possible), 4) induction with pentothal,
etomidate, or propofol supplemented with lidocaine, 5) pretreatment with a non
depolarizing muscle relaxant if succinylcholine is to be used and, 6) neutral head
position, (neutral in flexion, extension and rotation). Once a mask airway is established,
hyperventilation should continue to achieve a PaCO ranging from 25-28 mm Hg.
2
For anesthetic maintenance use drugs and techniques which have a minimal tendency
to increase ICP. These include IV anesthetics, narcotics, and muscle relaxants (avoid
drugs that induce histamine release). Nitrous oxide, isoflurane, desflurane, and
sevoflurane can likely be used in low to moderate dosages (1/2 to 1 MAC). During the
procedure the following are helpful in reducing ICP and brain swelling:

elevation of head

neutral head position (<60 head rotation, neutral in flexion and extension)

hyperventilation (PaCO 25-30 mm Hg)

oxygenation (PaO > 60 mm Hg)

low to normal CVP

low intrathoracic pressure (no peep)

good muscle relaxation (no cough or straining)
o
2
2
In addition, mannitol (.25-1.5 gm/kg) and furosemide (0.05-.1 mg/kg) can be extremely
helpful and should be given after consultation with the neurosurgeon. Optimally, this is
done during scalp incision such that the mannitol has at least 20-30 minutes before its
effect is needed. Mannitol works by osmotically drawing tissue water out of the brain
across regions of the brain with normal blood-brain barrier and excreting it via the
kidneys (avoid use in patients with renal failure). If a dilute diuresis does not result,
mannitol is likely not effective. Consider administering a small dose of furosemide (5-10
mg). Furosemide pulls water out of brain by affecting the Chloride-shift of the Na /K
pump and improves cerebral venous volume by causing a diuresis. Furosemide may
facilitate the action of mannitol by initiating a diuresis.
+
+
Fluid management: General agreement exists that cerebral edema is worse if large
amounts of fluid or if hypotonic fluids (e.g. D5W) are used. Note that lactated Ringers is
slightly hypotonic (about 90cc free water per liter). The general agreement is to use
fluids with normal sodium concentrations (normal saline or plasmalyte). Albumin 5% is
acceptable as long as the sodium content is normal (however, albumin or synthetic
Page | 12
colloids offer little value unless volume replacement is for rapid blood loss). Nonalbumin colloids such as Hetastarch, may cause coagulation problems. Maintain
normoglycemia and only administer glucose when glucose is low as hyperglycemia will
promote ischemic injury. The neurosurgical management generally involves avoidance
of hypervolemia, so avoid overhydration. If low urine output or hypotension occur,
additional fluids may be required to maintain cerebral perfusion pressure.
Monitoring--Customary monitoring includes arterial line (transducer zeroed at ear level
to reflect cerebral perfusion) and foley catheter in addition to usual monitors. A central
venous catheter (CVP) may be helpful to manage fluid status (and will be required if air
embolism is probable). The antecubital route is preferred as it is a relatively benign and
effective method for placement of a CVP unless large bore CVP’s or PA catheters are
used. A neuromuscular blockade monitor should be used as movement (especially
patient in head pins) could be dangerous.
Emergence - Very little pain usually occurs during the intracranial portion of the surgery.
Pain usually occurs at opening and closing. Thus, the level of anesthesia used for the
intracranial portion of the procedure may need to be increased during closure. Further,
hypertension commonly occurs during closing (not necessarily due to pain). In general,
it is desirable to have the patient awake and extubated (if appropriate) to be examined
neurologically shortly after the procedure. Consider methods to improve awakening time
after long craniotomies such as conversion of isoflurane to less soluble anesthetics
(desflurane, sevoflurane) and/or increased use of intravenous supplements (e.g.
propofol). Uncomplicated craniotomy patients usually return to their preoperative
neurological status (i.e. if the patient was not awake preop, they may not awaken postop). Antihypertensives should be used if the BP is unusually high (systolic > 160-180
depending on the surgeons’ concerns) and pain relief is appropriate, and there is no
evidence of hypoxia and/or hypercarbia. Extubation is highly desirable for neurological
examination if appropriate. Patients must be observed carefully for ventilatory
insufficiency and airway obstruction secondary to neurological or pharmacologic effects.
The first hour is usually the most concerning time so patients are usually observed in
the PACU despite going to the ICU. Often a CT scan is done immediately post-op after
PACU stay.
Special problems - The most likely intraoperative problem will be brain swelling. If this
occurs review the list above to ensure all is being done. Elimination of nitrous oxide and/
or reduction of inhalational agents may help. Intravenous thiopental (.5 - 1 mg/kg) may
also help but may cause delayed awakening if large doses are given (administer slowly
to avoid hypotension). The second most likely problem is low urine output (< 1/2
cc/kg/hr). Here the CVP becomes important; a low CVP probably indicates the need for
a fluid bolus (100 - 200 cc) to allow adequate circulatory volume. If the CVP is not low,
diuretics such as mannitol and furosemide may be preferred.
Page | 13
The Semi-sitting (lounge chair) position with the head elevated for routine craniotomies
Page | 14
POSTERIOR FOSSA SURGERY
Objectives:
Know the preoperative and intraoperative considerations for patients undergoing
skull base tumor resections including:
 Meningiomas
 Glomus jugulare tumors
 Pituitary tumors
Know general principles of positioning the patient for neurologic surgery and the
advantages and disadvantages of each position:
 Lateral
 Prone
 3/4 prone
 Supine- head neutral or head turned
 Sitting position (rarely used at this institutions)
Recognize the relative risks of different procedures and positions for air
embolism
Understand appropriate changes in anesthetic management in response to air
embolism
Detect and treat air embolism during neurosurgery
 Recognize precordial doppler sounds associated with air embolism;
recognize changes in end-tidal CO2, PA pressures, CVP and blood
pressure consistent with air embolism
Patients having surgery in the posterior fossa present several different challenges
including those of the sitting position and air embolism, which are discussed separately.
Note that general considerations for tumors (elective craniotomy) also apply. Note that
surgery in the posterior fossa can interact with brainstem structures causing physiologic
changes. Thus, our monitoring can act as a guide to help the neurosurgeon. Sudden
changes in pulse or blood pressure should be reported immediately to the surgeon.
Stimulation of these brainstem centers have been associated with these changes:






gasps and respiratory arrhythmias (respiratory center)
hypotension (Cardiovascular Center (C.V.) center, cranial nerve X)
hypertension (C.V. center, cranial nerve V)
bradycardia (C.V. center, dura, cranial nerve V, cranial nerve X)
tachycardia (C.V. center)
arrhythmias (C.V. center)
Bradycardia is seen most commonly and can also result from stimulation of the dura
(via vagal innervation). Atropine, although helpful, is best avoided as it may mask
Page | 15
detrimental surgical compromise of the brainstem structures. Occasionally atropine is
needed and even external pacemakers have been used in asystole (plan pacemaker
capability in patients with bradycardia preoperatively or with large tumors).
For patients undergoing posterior fossa surgery, postoperative considerations are very
important. The small amount of space in the posterior fossa and the critical structures
there give little margin for postoperative bleeding. Hypertension and severe coughing
or straining can cause bleeding. A typical scenario is a patient who postoperatively
has respiratory depression/unresponsive, is given naloxone, develops sudden
hypertension, a posterior fossa bleed, and further neurological deterioration.
If the surgery involves damage to lower cranial nerves, the patient may have compromised airway protective reflexes post- peratively. In these patients, extubation should
be carried out with a great deal of caution. Be aware, if damage to the respiratory
center has occurred, the patient may have no respiratory drive. Fortunately, this is
most uncommon.
A second major concern is cranial nerve injury in posterior fossa surgery. During
surgery, the surgeons may wish to monitor cranial nerve function by EMG monitoring.
This necessitates the omission of muscle relaxants so as to measure EMG or observe
facial nerve function. The need for this is best identified pre-op and the induction
relaxants allowed to dissipate at the appropriate time. For anesthesia with limited
muscle relaxants, a moderate dose of inhalational agents (i.e. isoflurane) may be
helpful to prevent patient movement. TIVA is also an option using adequate
sedatives/narcotics.
For EMG recordings of the facial nerve, needle electrodes are placed in the facial
muscles. The facial nerve is commonly of concern and the surgeon may stimulate it and
ask for observation of ipsilateral eye (orbicularis oculi) or mouth (orbicularis oris) motion.
It is important to differentiate jaw jerk and shoulder shrug from eye and mouth motion.
Prone position for posterior fossa surgery
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SITTING POSITION
Although it is being used rarely these days, the sitting position is favored by many
neurosurgeons because: 1) venous bleeding is reduced by gravity and 2) anatomy is
oriented easily making surgery on the neck and brainstem easier to conduct. The
disadvantages have prompted most surgeons to use the prone or lateral position for
these cases.
From an anesthetic standpoint the disadvantages form the basis of concerns of
management and are as follows:
Hypotension - often described as one of the most common problems, this is due
to gravity reducing venous return. To minimize this: a) gradually adjust to the sitting
position trying to keep the knees at heart level, b) use compression wraps (ace) or
sequential compression boots on the legs c) use light anesthesia until in the sitting
position d) correct severe fluid deficits prior to sitting and, e) place patient supine if
hypotension persists in spite of all other measures.
Air embolism - see separate section; this is the classic problem for this position.
Quadriparesis-a rare complication that appears to be due to excessive neck
flexion. Try to minimize flexion such that there is at least 1-2 finger breadths between
jaw and sternum.
Massive tongue swelling - also rare, it appears to be reduced by not using an
oral airway and avoiding excessive neck flexion
Injury from positioning
a) make sure the horseshoe head holder or Mayfield tongs do not press on the forehead
or nose - recheck when position is changed.
b) avoid putting stretch on the face with tape that could injure the face - tape the circuit
to the head holder to reduce strain on the endotracheal tube
c) support the elbows to avoid the weight of the arms causing brachial plexus stretch
d) pad and position the hands comfortably across the waist
e) make sure the buttocks are well seated in the crotch of the table so there is no low
back strain
f) make sure hip flexion and knee flexion is adequate so as to reduce sciatic nerve
stretch
g) carefully pad the knees and legs to avoid pressure on the upright holder for the
Maryfield
h) pad the calves and heels to prevent pressure injury to the heels
Be careful to note how to manipulate the table if needed to position the patient head
down for air embolism. Usually the whole bed needs to be moved (with trendelenburg)
so that the bed moves as a unit. Just moving the back of the table down will often
“hang” the patient by the head holder putting severe strain on the neck. Note position
of Mayfield before sitting patient up.
Page | 17
Page | 18
AIR EMBOLISM
In general, if the operative site is more than 5 cm above the atrium, air entrainment
through the operative site can occur. Entrainment is very common through bone or
large venous sinuses since these structures cannot collapse. Procedures recognized for
their risk of air embolism include sitting position cases, transphenoidal surgery in the
semi-sitting position, and some cases of lumbar laminectomy (when the abdomen
hangs free lowering the CVP). In addition, some craniotomies in the supine or semisitting position may also have risks of air embolism (especially in children).
The most important aspect of management is detection of air embolism. The routine
monitors that should be used for detection are (in order of sensitivity):
1.
Precordial Doppler - the traditional sounds can warn of amounts of air that are
usually less than a problem to the patient (unless they get to the left sided circulation).
The Doppler should be placed on the chest using Doppler jelly at the edge of the left or
right sternum in the 3-4, 4-5, or 5-6 intercostal spaces. Listen for optimal sounds of
great vessel and heart motion with each heart beat. To confirm that the vascular
structure being monitored is the vena cava, inject 10 cc of saline (shake the syringe to
introduce “microbubbles”) in the CVP. Reposition if the sounds are not heard.
Document this test of position on your record.
2.
End tidal CO2 - generally considered next most useful, a sudden unexplained
drop in ETCO2 may signal increasing dead space from pulmonary arterial obstruction
from entrained air. Note that changes in ventilation (e.g. hyperventilation) or blood
pressure (i.e. hypotension) can mimic this change.
3.
CVP - a sudden, unexplained rise in CVP can signal pulmonary arterial
obstruction from air. In addition blood withdrawal via the CVP can document air
embolism by noting air bubbles (be sure the tubing connections are tight). Further
aspiration via the CVP may remove a large amount of air if done promptly during the
embolism. To be optimal, the CVP tip should be multiorificed and placed 2-3 cm above
the atrio-vena caval junction. You should document how you confirmed this position of
the catheter on your record (e.g. x-ray or electrocardiographic).
When using the ECG from the CVP catheter, connect an ECG lead to the catheter.
The easiest is the chest lead for a V5 display. Be sure to remove air bubbles from the
catheter. The best tracings are obtained if the catheter is filled with sodium bicarbonate
(better electrical conductivity - equal to 3% saline). First adjust the catheter to get a
large P wave to be sure you are near the heart and then adjust to a biphasic P
(confirming position at the SA Node. Then pull back 1-2 cm.
Page | 19
TRANSPHENOIDAL PITUITARY RESECTIONS
Most pituitary tumors are non-secretory or secrete prolactin. As such, only injury to
normal pituitary by a mass effect causes endocrine dysfunction. Some tumors cause
clinical changes, the most common is growth hormone secretion with acromegaly. A
preoperative endocrine work up will reveal hormonal dysfunction that may require
steroids or hormones replacement. A very high prolactin level may indicate invasion of
the cavernous sinus by the tumor.
The growing mass causes the optic chasm to be compressed and produces the typical
bitemporal hemianopsia. Usually ICP is not elevated unless the tumor is extremely large
(usually a craniotomy will be needed for resection in this case). It is best to identify
raised ICP preoperatively and treat those patients accordingly.
Induction for the procedure is normal, requiring only an intravenous line. A routine
intubation is fine, unless the airway is a problem (such as with giantism). Most people
prefer an oral RAE tube draped out of the middle or corner of the mouth to minimize the
interference with the surgery. Avoid taping the tube such that the facial symmetry is
distorted as a common postoperative complaint is a crooked nose. If sufficiently head
up, air embolism is possible (via opening the cavernous sinus or other venous
channels). In such a case, an arterial line, CVP, ETCO2 and precordial doppler should
complement the basic monitoring regimen. As usual, the arterial transducer should be at
head level.
Rarely, surgeons request a spinal drain for the procedure. It is usually placed be placed
pre-induction. It is used for drainage of CSF after surgery if there is a dural leak, or for
injection of air during surgery to highlight the tumor on fluoroscopy (avoid nitrous oxide
after this injection) or to inject fluid to push the tumor down into the operative field (be
very cautious about what you inject!). Valsalva maneuver can also push the tumor
down by increasing CSF pressure.
Position: The patient will be semi-sitting (lounge chair) with the head elevated and
o
pointed to the right (10 ). Note that surgical access to the thigh may be needed for fat
removal that is placed in the nasal cavity prior to closing.
Anesthetic Maintenance: No particular anesthetic type is superior as long as ICP is not
elevated. Local anesthesia is usually applied to the nasal mucosa, so that a light
anesthetic is often adequate.
Fluids - There are no unusual fluid requirements unless again ICP is raised. The urine
output and CVP (if available) should serve as a guide to maintenance fluids. Keeping
maintenance fluids to a reasonable and minimal amount will prevent excessive urine
output that could be confused with the diuresis of diabetes insipidus (which is a
common postoperative occurrence).
Page | 20
CAROTID ENDARECTOMY (CEA)
Objectives:
Understand anesthetic concerns for patients undergoing extracranial
neurovascular surgery (such as carotid endarterectomy).
Know cardiovascular concerns in the preoperative evaluation of these patients
Learn to evaluate the cerebral circulation completely (vertebral and carotid
circulations) and know how patients with different types of extracranial
neurovascular lesions may have different anesthetic consideration
Be familiar with both regional and general anesthetic techniques for carotid
surgery as well as the advantages and disadvantages of each technique.
Be familiar with the different choices for neurologic monitoring during carotid
surgery as well as the advantages and disadvantages of each technique
including:
 EEG
 Evoked potentials
 Transcranial Doppler Ultrasound
 Cerebral Oximetry
 Awake neurologic examination
CEA is performed by neurosurgeons, vascular surgeons and occasionally by other
surgeons and represents a major anesthetic challenge. It must be remembered that the
major operative risk is stroke, but the major mortality risk is myocardial infarction. Hence
careful pre-op scrutiny of myocardial, carotid and cerebral vasculature must be
conducted in addition to the usual evaluation. On very few occasions, a patient’s
myocardial status may require a pulmonary artery catheter for optimal intraoperative
management, as is the case in a combined carotid/CABG procedure. The discussion
below will deal with the routine carotid where the myocardial risk is not considered high.
Note, however, in a combined CEA-CABG that a fresh stroke with the CEA is uniformly
fatal (to the brain) during by-pass so CEA management is critical.
Preoperatively, premedication should be tailored to the patient and is often useful. Give
the patient’s cardiac and anti-hypertension medications, if appropriate. Intraoperative
monitoring should include A line (due to wide blood pressure swings), ETCO (to adjust
ventilation to normal PaCO ), EKG to detect ischemia (II and V5 or as best for the
patient) and some form of cerebral monitoring for ischemia (such as EEG). For patients
who may be labile, an IV access with “low dead space” should be available and an
2
2
Page | 21
antihypertensive infusion (such as nitroprusside) and pressor (such as neosynephrine)
hooked in, ready to use. Placement of central line may be indicated in some patients.
Rarely, a jugular CVP is used as patients may be dependent on the non-operative
carotid artery for cerebral perfusion. If used, don’t place it on the operative side; the
subclavian route may be preferred in patients with bilateral carotid disease.
Some clinicians prefer to conduct CEA using regional block (deep or superficial
cervical plexus block), but the majority are done here with general anesthesia. Awake
CEA has the advantage of excellent neurological monitoring during the procedure.
However, a superficial cervical plexus block may be helpful with postoperative pain.
Induction of general anesthesia should be chosen based on cardiovascular and
myocardial reserves. Hence thiopental, propofol, etomidate, midazolam, fentanyl, etc.
have been used. The goal should be adequate anesthesia without marked hypotension
and without marked hypertension on intubation. Hence, usually some narcotic base is
useful; inhalational anesthesia to provide afterload reduction to help control blood
pressure, reduce cerebral metabolism and insure an asleep patient. Isoflurane is usually
chosen because it is less myocardial depressive and most cerebral depressant.
Maintenance of anesthesia is best achieved with the following goals:
1) keep end-tidal CO2 near normal
2) keep blood pressure in the high normal range for this patient (i.e., blood pressure
as measured in the OR by the same method.
3) try to keep a steady level of anesthesia if possible, if EEG is being recorded
4) avoid marked hypertension, especially after the carotid is open as intracranial
hemorrhage can occur.
Note also that what may be needed to reduce myocardial demands may conflict with
cerebral needs. But, when possible, keep the blood pressure in the high normal range
to maintain cerebral perfusion and the heart rate normal (not increased) to reduce
myocardial oxygen demands. Monitor for cerebral ischemia whenever possible. Critical
times are:
1) positioning-as hyperextension of the neck can kink the vertebrobasilar artery that
can be a major supply in bilateral carotid disease (you can check this preop!)
2) cross-clamping of the artery prior to opening the artery
3) kinking or obstruction of a shunt if placed
Page | 22
4) cross-clamping prior to closing the arteriostomy
5) hypotensive episodes.
If signs of ischemia occur, alert the surgeon; if possible, raising the blood pressure may
help (if myocardial risk or risk of intracerebral hemorrhage is not high).
Monitoring for ischemia during cross-clamping can be done by several methods. These
include awake surgery, EEG and TCD (see separate sections), and stump pressure.
The latter is done by connecting a sterile high pressure tubing to the arterial line
transducer stopcock and recording the pressure in the carotid before and after the
cross-clamping. MAP less than 25 mmHG is usually bad and above 50 mmHg signalling
adequate intracranial collatterals.
Placement of a shunt is equivalent to a 70% stenosis, but carries risks of dislodging
emboli, a false sense of security if the shunt clots or kinks, and usually increases the
complexity and duration of the procedure.
At the conclusion of the procedure, be prepared to treat hypertension which usually
occurs. Attempt to awaken in the O.R. so that neurologic exam can be done; good arm
movement contralateral to the operated site is usually the most important first sign.
Note that the largest number of strokes are small ones due to emboli (air or plaque) and
may not be detected (usually discovered as neuropsychiatric changes). We can often
detect and correct major vascular ischemia from inadequate CBF during cross
clamping. Although this is a minor numerical contribution to stroke, outcome is often
devastating. Note about 30% of strokes are due to clots in the operative site and
therefore have their onset immediately after surgery (such as recovery room) so that
exploration of the surgical site may be emergent.
Note a hematoma in the surgical site can cause airway compression that is relieved by
cutting open the dressing and opening the surgical site. A neck hematoma may also
make intubation difficult if it is necessary to take the patient back to the OR for exploration of the surgical site for postoperative bleeding.
Carotid body injury may occur postoperatively, thus if a patient has had bilateral CEA’s,
prolonged supplemental oxygen may be required. Cranial nerve injury may also occur
following CEA: recurrent laryngeal nerve resulting in hoarseness, hypoglossal injury
resulting in tongue deviation on protrusion, and marginal mandibular nerve injury
resulting in drooping of the corner of the mouth.
Page | 23
INTRACRANIAL VASCULAR SURGERY
Objectives:
Know the following concepts regarding aneurysmal subarachnoid
hemorrhage:

Acute CNS physiology changes with subarachnoid hemorrhage

The natural history of subarachnoid hemorrhage, specifically regarding
advantages of early versus delayed surgery

Know potential effects of subarachnoid hemorrhage on the function of other
systems including the cardiovascular system, pulmonary system and renal
system

Evaluate the neurologic status of the patient with subarachnoid hemorrhage
and intracranial aneurysm by means of the Hunt-Hess grading system

Recognize preoperative vasospasm as well as identify patients at risk for
developing vasospasm; be aware of proposed mechanisms for vasospasm
as well as current accepted therapy (including calcium channel blockers,
lazeroid compounds and hypertensive, hypervolemic hemodilution

Understand which patients are likely to require special techniques such as
barbiturate protection, hypotension, induced hypertension, or temporary vessel
occlusion
Know the natural history and treatment options for arteriovenous malformations. Be
aware of the importance of preoperative blood flow through the AVM with respect
to potential need for induced hypotension or other techniques to reduce
“breakthrough” bleeding.
This section includes discussions on intracranial aneurysms and AVM. We will first
address intracranial aneurysms. Intracranial aneurysms represent a challenge to
both the anesthesiologist and the surgeon. A close working relationship is
essential, especially with respect to blood pressure control and coordination at the
time of clipping.
Philosophically speaking, the anesthesiologist has four major concerns. These
are, 1) preventing rupture, 2) allowing exposure, 3) maximizing circulatory
blood flow and 4) brain protection.
Page | 24
1) Since uncontrolled rupture of the aneurysm represents a very real threat to life, it
is usually the focus of attention. The determinants of rupture are high blood
pressure and low ICP, as such attention should be focused on these variables.
In particular, hypertension presents the greatest threat. Therefore, carefully
controlled blood pressure is essential. In past, deliberate hypotension was
utilized (usually with sodium nitroprusside), but concerns about cerebral ischemia
have given way to “controlled normotension”. Hence we need to discuss with the
surgeons and agree on a blood pressure range for case management (this is
usually the lower range of the preop normal as assessed by the same technique
(cuff or a-line).
Since clearly the most dangerous problem is sudden hypertension, the availability of a rapid way to lower blood pressure is helpful. It is notable that sudden
hypertension can occur with a) induction, b) intubation, c) Mayfield head holder
placement (pins), d) skin incision, e) dural opening and f) aneurysm dissection
and exposure. Because these occur before surgical control of bleeding is
possible, anesthetic management is key. Some anesthesiologists prefer deep
anesthesia to avoid sudden hypertension (but without hypotension). Some
surgeons will utilize temporary clipping of the major artery feeding the aneurysm
prior to clipping. In this case deliberate hypotension may not be desirable and,
in fact, deliberate hypertension may be preferable. Means for short term
elevation for blood pressure should be available (such as bolus neosynephrine).
Since sudden decreases in ICP can promote rupture, do not allow a CSF drain
(if present) to be open unless the surgeons request it (usually not until the dura
is opened) and keep track of the volume drained to avoid excessive withdrawal.
2) As usual with craniotomies, considerations apply to reduce brain congestion and
facilitate the surgical exposure. Thus the principles listed for craniotomy and ICP
control apply. Note that cerebral swelling can be a particular problem with these
cases as blood from the SAH can cause excessive swelling and excellent
exposure is needed to provide access to the base of the aneurysm. Since
excessive hyperventilation can contribute to cerebral ischemia, hyperventilation
is usually restricted (PaCO 30-32). Sodium thiopental can assist in reducing
cerebral swelling. Note (below) some surgeons may use a CSF drain to help
with exposure.
2
3) Methods to facilitate microcirculatory blood flow are key to perfusion of the brain
in the face of ischemia and vasospasm. Maintenance of adequate blood
pressure, avoidance of excessive hypocarbia and adequate oxygenation have
been discussed. Hypercarbia and cerebral vasodilators are avoided because
they may “steal” blood from vessels that are spastic or have lost autoregulation.
Mannitol may help by reducing blood viscosity as well as hemodilution with goal
hematocrit of 30-32.
Page | 25
4) Brain protection may be key in protecting the brain from ischemia if temporary
clipping, hypotension, or rupture occurs. Traditional methods have focused on
cerebral metabolic depression. To assess this, many individuals utilize the EEG
and look for burst suppression. Traditionally this is accomplished using
isoflurane or thiopental. Thiopental has additional advantages over propofol of
free radical scavenging. In cases involving hemorrhage (as a result of rupture),
a growing appreciation of hypothermia suggest that it may be more valuable,
o
even if only to moderate degrees (34-35 C). Hypothermia not only reduces
cerebral metabolic rate, but also inhibits excitatory amino acid release. Since
SAH may cause hyperthermia, cooling may be useful even if to lower the
temperature to normal. Plan on cooling using a cold water blanket beneath the
patient and a cold air blanket above (Bair Hugger). In patients with
o
uncomplicated aneurysms, normothermia (36-37 35 C) is the goal.
The case management begins with the pre-op visit where the aneurysm location and
patient neurological grade are identified. Location is important for position and usually
position will be supine except for basilar artery aneurysms which will require special
considerations (such as prone position). Neurological grades will identify the risk
assessment - if the patient has major neurological deficits then one must be very careful
as ischemia and cerebral injury have been prominent. Most patients are operated on in
the supine position (beach chair) with the head turned so the surgical incision can be
made on the temple. To avoid excessive neck rotation, consider rotating the body with a
shoulder roll under one shoulder (semi lateral position).
Premedication is often light, but may be indicated if unnecessary anxiety causes
hypertension. Prior to induction, an arterial line should be inserted to observe
hyperten sion with induction. A CVP is very useful but can usually be inserted after
induction. The surgeons may desire a S.G. catheter postop, but a long arm catheter
is usually sufficient for the operative course. After induction the surgeons may wish
the patient be placed lateral for a lumbar spinal drain placement; this should remain
closed until the surgeon requests drainage to improve exposure by drainage of the
lateral ventricule (usually at dural opening). Identify with the surgeon what blood
pressure is desirable for the case. Be cautious of blood pressure rises, especially at
induction, intubation, head holder placement, and incision. Judicious anesthetic
choices (including narcotics on induction) can prevent rises; bolus thiopental can
help stop a rise in progress. Mannitol and lasix will likely be used during
craniotomy; consider fluids that are appropriate with any craniotomy. Cooling
blankets will be beneficial; note body temperature will likely drift 0.5-1.0 degrees
centigrade after cooling is stopped. Begin warming after the aneurysm is clipped.
During dissection be sure that you have at least one good IV for blood transfusion and
blood readily available. Remember, rupture does not indicate a need to transfuse. The
actual blood loss should be observed (recall the surgical field is magnified) and keep in
Page | 26
mind that oxygen delivery is optimal at an Hct of 30-32. If possible, a bolus dose of
thiopental one minute prior to clipping or temporary clip placement may afford extra
protection. Be prepared to raise the blood pressure if a temporary clip is used; the
surgeon will request it if needed.
During closure, discuss appropriate blood pressures for post-op care so you can begin
to adjust for this at the conclusion of the case (~ 20% of patients have a second
aneurysm).
Vasospasm remains a major cause of morbidity and death even after otherwise
uneventful aneurysm clipping. It manifests by a new focal deficit or decreased level of
consciousness. Attempts to prevent neurologic deficits from vasospasm by preoperative
use of calcium-antagonists (nimodipine) may be indicated (discuss with surgical team).
Once it develops, vasospasm is initially treated with volume therapy (CVP increased to
10-12 mm Hg or PCWP to 15-18 mm Hg). If this does not reverse the neurologic deficit,
BP is elevated pharmacologically (systolic BP 160-180 mm Hg) if tolerated.
At the conclusion of the procedure, attempt to awaken the patient and extubate when
possible and appropriate, so that neurological status can be observed. Rewarming (if
applicable) may be key to awakening the patient.
AV MALFORMATIONS
AV malformation resection is similar to intracranial aneurysm management and most of
those principles apply. However, there are a few important differences.
First, deliberate hypotension should not be used. The AVM acts as a low pressure
bypass such that adjacent areas of the brain may receive inadequate cerebral blood
flow at normal pressures. With deliberate hypotension, ischemia may occur such that
the brain may be placed at risk. So in general, hypotension is undesirable.
A second difference is blood loss. Whereas blood loss with an aneurysm is generally
not excessive (unless during a brief period if the aneurysm should rupture), the blood
loss of an AVM resection may continue for a substantial period of time. Hence, having
good venous access for transfusion, a central venous monitoring line to determine
central volume and a watchful eye on urine output and blood loss is important. Fortunately, preoperative plugging of the AVM by neuroradiological methods has substantially reduced OR blood losses.
Third, once the AVM is resected, blood flow to the previously deprived cerebral tissue
may now be increased. If that tissue was previously ischemic, the blood brain barrier
may not be normal. Hence the brain will be more prone to cerebral edema and
hypertensive cerebral hemorrhage (known as reperfusion breakthrough). Hence, post
resection hypertension should be avoided as should excessive use of hypoosmotic
Page | 27
fluids. Consultation with the neurosurgeon should allow identification of postoperative
blood pressure goals.
Page | 28
SPINE SURGERY
Objectives:
Be able to differentiate between radiculopathy and myelopathy as causes of CNS
generated pain and/or muscle weakness.
Recognize which patients with spinal cord pathology may require special
techniques such as awake intubation and positioning.
1) Intubate an awake patient such that coughing or movement are
minimal.
2) Master anesthesia for awake intubation, including but not limited to at
least one of the following techniques: appropriate use of drying and
sedative/analgesic agents, topicalization techniques, superior
laryngeal and glossopharyngeal nerve blocks and transtracheal
injection of lidocaine.
Be able to describe the following different types of spinal operations as well as
their anesthetic implications with respect to purpose, relevant anatomy, degree
of complexity and anesthetic complications:
 Anterior cervical discectomy and fusions, anterior cervical corpectomies,
posterior cervical fusions, laminectomies, and foraminotomies
 Laminectomies for excision of spinal cord tumors, both intramedullary
and extramedullary
 Thoracic and lumbar laminectomies and fusions (PLIF, ALIF, TLIF
AxiaLIF), microdiscectomies and corpectomies.
Be familiar with anesthetic techniques that will facilitate neurologic monitoring
techniques such as somatosensory evoked potentials, spontaneous and
evoked EMG monitoring and motor evoked potentials.
Repair of traumatic cervical spine injuries (different approaches) and specifically
be aware of anesthetic implications of acute spinal cord injury
Know how to evaluate patients with spinal cord injury at any level. Be aware of
disruption in normal CNS, cardiovascular, and pulmonary physiologythat can be
caused by acute spinal cord injury and what impact this disruption has on
appropriate monitoring and anesthetic management.
Apply appropriate techniques for airway management in the patient with spinal
cord injury.
Evaluate patients for suitability for extubation considering CNS and other organ
system pathology induced by the trauma.
Know anesthetic considerations in the patient with chronic spinal cord injury
undergoing neurologic or non-neurologic surgery including:
Page | 29

Autonomic hyperreflexia - what patients are at risk and how may this
syndrome be prevented and treated
Know changes in neuromuscular function induced by chronic spinal cord injury
and the impact these changes have on anesthetic management
The implications of spine surgery rest on the location (cervical, thoracic, lumbo-sacral),
pathology (radiculopathy, stenosis, spinal cord injury, spinal deformity,
tumor/metastasis) and position (lateral, prone, supine).
Location: Cervical surgery can be conducted prone or supine. For cervical procedures,
preoperative consultation with the surgeon is important, not only because of position
considerations, but also about intubation and induction. In addition to the usual airway/
intubation considerations, the surgeon may request an awake intubation with awake
positioning. If these are requested, neurological function (moving arms and legs on
command) should be documented after intubation and positioning.
Except for transabdominal, extraperitoneal approaches to the lumbar spine, (where the
usual spine considerations apply), anterior cervical procedures are the only frequent
supine procedures in the supine position. Here considerations mentioned above apply
for anterior cervical procedures including arm placement at side. Also notable is that a
surgeon’s arm may rest on the face causing pressure injury and kinking of the
endotracheal tube.
If the surgical procedure on the cervical spine is anterior, the approach is usually via the
right neck. Retractors are used to expose the spine. These retractors can cause kinking
of the carotid artery. To monitor this, one should periodically feel the temporal artery
pulsations - especially when the retractor is placed or adjusted. Be sure to place an
OG/NG and/or esophageal stethoscope to help the surgeon identify the esophagus.
Post surgically be aware of tracheal, laryngeal nerve and esophageal injury, particularly
if the procedure is very high (C2-C3). Occasionally a trans-oral approach may be used
for C1 odontoid procedures. In these cases a tracheostomy may be conducted initially. If
vocalis EMG is requested for anterior cervical spine procedures, use the Zomed
endotracheal tube and avoid muscle relaxants during the case.
In addition to the obvious prone considerations, the prone position has several
potentially serious problems. First, caution must be made in positioning of the male
genitals and female breasts (no pressure on nipples). Head position must be carefully
done. For cervical and high thoracic procedures the head should be neutral on a foam
block, horseshoe head holder or Mayfield tongs. Periodically check the face when
prone, massage areas where pressure injury may occur (e.g. chin). Post operative
visual loss (POVL) can occur via mechanisms that remain largely unknown.
When prone, the arms may be positioned up by the head on arm boards for low
Page | 30
thoracic or lumbosacral procedures. However, for high thoracic or cervical prone
procedures the arms must be positioned at the patient’s side. In this case lines (IV’s
and arterial line) need to be anticipated and placed before positioning. Two IV’s may
be desirable when arms at the side, in case one becomes dysfunctional during the
case.
The prone position has become known for some unexpected deaths due to air
embolism. These appear to occur because the surgical field is sufficiently above the
atrium to allow air entrainment. When prone, abdominal pressure may obstruct venous
return via the vena cava and promote epidural venous bleeding reducing the chance of
air embolism. Although this bleeding is undesirable, the opposite (the abdomen
hanging free) can cause negative abdominal pressure due to gravity that enhances the
gradient increasing the likelihood of air embolism. Hence, air embolism monitoring and
precautions need to be taken in the prone position when positioned this way (when
position or frames allow the abdomen to hang free).
Surgery on the lumbosacral spine is frequently done in the prone position. However,
during ALIF or TLIF procedures the position is anterior or lateral respectively. The
arms will be on arm boards up towards the head. Thoracic spine procedures can be
conducted prone (arms to the side) or lateral through the chest (thoracotomy). If via a
thoracotomy, a double lumen tube may be requested. Also, if lateral, the diaphragm
may be surgically opened and closed. If this occurs, post-op ventilation may be
necessary to reduce the strain on the diaphragmatic suture line. In addition, some
patients after thoracic spine instrumentation surgery (whether prone or lateral) may
not breath properly due to pain. Their breathing is usually dyscoordinate with shallow
tidal volumes. If this is the case, postoperative ventilation may be needed usually the
problem resolves in 12-24 hours.
Pathology: In general, radiculopathy procedures are on relatively healthy, young
individuals; blood loss is often mild. Multilevel radiculopathies or laminectomies for
spinal stenosis carry more blood loss (usually not excessive) and patients are often
older, sicker and debilitated (if excessively debilitated succinylcholine may be
contraindicated). Spinal cord injury is often associated with an unstable vertebral
column that may necessitate awake intubation (instabilities above T4) and cautious
positioning (such as awake positioning). If neurological injury is substantial (acute spinal
cord injury) succinylcholine may be contraindicated (between one day and one year
after injury). A variety of other acute and chronic medical considerations also apply.
Correction of spinal deformities, as well as some major spinal cord injury procedures
(notably lumbo-thoracic) can be associated with substantial blood loss. Here good
venous access, an arterial line and central venous access may be needed. Cell
salvaging may be very helpful.
Page | 31
Some surgeons request deliberate hypotension during spinal procedures to reduce
blood loss. If, however, the spinal cord is abnormal or injured, vascular auto
regulation may be lost or hypoperfused (when injured) such that the cord is pressure
sensitive. In these cases deliberate hypotension and hyper/hypocarbia may be
detrimental. In general, use normal ventilation and blood pressure levels.
If the spinal procedure is for primary or metastatic tumor, blood loss can be massive
(especially if metastatic renal cell carcinoma). For these procedures, preparations for
the blood loss is essential. Often cell salvaging is not used because of the fear of
reinfusing cancerous cells.
The anesthetic choice for spinal surgery is usually not critical. However, considerations
should be given to choice of anesthetic when the following are required 1) awake
intubation, 2) awake positioning, 3) prompt postoperative awakening and 4) monitoring
with EMG, SSEP and MEP.
SSEP monitoring will require TIVA using a narcotic or ketamine based anesthetic and
sedative and /or only low dose inhalational anesthetic. If motor evoked potentials are
used the anesthetic will likely need to be totally intravenous and muscle relaxants may
need to be avoided.
In general, it is highly desirable to have the patient sufficiently awake after spine surgery
to examine neurological function as soon as possible (especially in the O.R.). This is
because unexpected paralysis can often be reversed if the problem is corrected quickly
by re-operation (usually 3-4 hours). Note that extubation is not needed, just sufficiently
awake to follow commands. In general, delayed extubation is desirable with cervical
surgery. This is because it is highly undesirable to emergently reintubate using direct
laryngoscopy since the mechanical motion of the neck may damage the surgical
procedure or not be possible if a halo brace has been placed.
The Prone Position for Cervical/Upper Thoracic Procedures
Page | 32
DEEP BRAIN STIMULATOR PLACEMENT FOR PARKINSON’S
DISEASE
Objectives:



Understand the indications for electrode placement
Keep in mind the issues involving providing anesthesia in a remote
location such as the MRI suite
Know the surgical complications associated with this procedure and how
anesthetic management affects them.
Without any medications except local anesthesia and propofol in MRI, this procedure
involves deep brain stimulation via electrodes of generally, the thalamus, subthalamic
nuclei or globus pallidus to interrupt the motor pathway involved in Parkinson’s
movement. Sedation in MRI is needed to reduce motion artifact in order to get an
adequate target location for the subsequent electrode placement. During electrode
placement, active movement is needed as a marker to identify proper electrode
placement. Since this movement is easily stopped with anesthetic agents, medications
must be avoided except during the MRI.
This procedure is increasing in use because of effectiveness and relatively benign
nature of the procedure. Candidates include patients who are not adequately treated by
available medications or have unacceptable side effects on those medications.
Part I MRI
Some patients undergoing MRI require sedation. The anesthesiology personnel should
accompany the patient into the MRI room to keep an eye on the patient. When entering
the unit, be careful to not take metal objects in: they can be propelled into the unit and
cause harm, or be damaged by the magnetic field (especially watches and credit cards).
In the MRI, monitoring is available with a non-invasive BP and pulse oxygen saturation
as well as visual inspection of breathing. Oxygen is supplied via the nasal cannula from
stainless steel tanks in the room or larger cylinders outside the room.
The main anesthesia task in the MRI is to sedate the patient (propofol) to prevent
movement of the head during the scan. Some body movement from the Parkinson’s
can be tolerated because the head is somewhat restrained, but moderate motion will
cause a blurred image preventing adequate acquisition of images. Sedation may also
be needed to help the patient tolerate lying on the table for an hour or so or if
claustrophobia is a problem. Propofol is typically administered by infusion. A special
infusion pump is needed to work in the MRI area and it must be kept at a distance from
the scanner. Infusion rates are usually 25-75 mcg/kg/min and need to be titrated to
effect.
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Part II Leksell Frame placement/ CT Scan
At our institution, the MRI is completed days in advance of the DBS electrode
placement. The patient does get a CT scan on the morning of surgery with the Leksell
frame placed by the surgical team. The anesthesia personnel are not involved in this
part.
Part III Electrode placement in the OR
The patient is returned to the OR and placed on the OR table. At this time monitors
should be placed including A-line (for patients with hypertension) and foley catheter with
sedation. The patient will then be attached to an immobile frame via the Leksell frame.
Ensure that the patient is comfortable, pressure points should be padded prior to start of
procedure. Oxygen should be supplied via nasal cannula and sedation provided while a
burr hole is created. After the burr hole is placed on the skull, then a probe inserted and
electrical stimulation done through the probes to confirm the location. Stimulated motor
activity (including writing) or cessation of the tremor helps confirm location.
Preop and intra-op, avoid benzodiazepines (patients are typically elderly and sensitive
to benzos) which can alter sensorium. In addition, keep patients normotensive with goal
SBP< 140 to reduce the risk of intracranial hemotoma. To achieve this, use nicardipine,
nitroprusside or hydralazine. Avoid beta- blockers as it can skew intra-op neurological
exam findings. (Keep in mind that the patient may need lots of TLC as these can be
long, uncomfortable cases).
In the unlikely event that intracerebral disaster occurs (such as blood vessel rupture),
the major problem is airway management. Perhaps the fastest way to ventilate is by
LMA, which could also serve as a track for fiberoptic intubation. Taking the patient out of
the Leksell frame apparatus off may take several minutes.
Once the procedure completed patients are admitted for neurological observation.
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Patient in Leksell frame on OR bed
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AWAKE CRANIOTOMY FOR EXCISION OF SEIZURE FOCI
Objectives :
Understand and anticipate preoperative and intraoperative anesthetic
considerations for patients undergoing electrocorticography and be familiar
with techniques for ‘awake’ craniotomies for patients undergoing resection of
pathology near eloquent structures.
Know the airway and sedation requirements for stereotactic neurosurgical
procedures conducted with either general anesthesia or monitored anesthesia
care
INDICATIONS FOR EPILEPSY SURGERY
a. The identification of an isolated seizure focus or “epileptogenic zone” in
area of relatively dispensable brain. The planned resection must preserve
motor and sensory function in the upper/lower extremity, language, and
memory.
b. The seizures have proven unresponsive or “medically intractable” to an
adequate trial of anticonvulsant therapy.
c. The seizures severely interfere with the quality of life and functional
capacity of the patient.
d. Epilepsy surgery offers a reasonable opportunity to provide improved
medical control or total elimination of seizures with improved quality of life
and functional status for the patient.
1)
2)
3)
4)
ANESTHETIC GOALS
To provide for the comfort and safety of the patient:
Establish rapport with the patients.
Educate the patient with respect to the stages of the operation and the role of
the anesthesiologist as a member of the epilepsy team.
Maintain adequate spontaneous ventilation and stable hemodynamics during the
entire surgical procedure.
Recognize and appropriately manage intraoperative seizures
 Have propofol or thiopental readily available for bolus.
To facilitate the surgical procedure:
1) Optimize surgical exposure with mannitol, lasix, etc., as needed
2) The patient should be awake and participating during mapping and comfortable,
quiet, and still at other times.
To facilitate the intraoperative assessment during the resection:
1) Use medications which do not alter the seizure threshold or interfere with the
intraoperative EEG (especially benzodiazepines).
2) Tailor the anesthetic technique to facilitate a smooth and rapid emergence prior
to intraoperative testing. The patient should be awake, comfortable, and
appropriate for testing.
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During craniotomy, the patient will require sedation. The typical anesthetic agents
include propofol and remifentanil infusion as these have rapid onsets/offsets. The actual
operating procedure is divided into six stages: Craniotomy, Corticography, Functional
mapping, Cortical resection, Post resection EEG and Closure.
Craniotomy
The patient is usually positioned comfortably in the supine position (shoulder roll is
sometime placed to achieve a semi-lateral position) on the operating table with the
head in Mayfield pins. Pressure points should be padded. Monitors are placed and
oxygen is administered with a nasal cannula with capnography monitoring. Propofol
and Remifentanil infusions are titrated to an appropriate level of sedation. A foley
catheter should be placed after adequate sedation is obtained. The sterile drapes
should be positioned so as to allow full access to the patient’s face for airway
management and adequate ventilation. In addition, this will decrease claustrophobia
and facilitate intraoperative motor and speech mapping. Discontinue the propofol
and narcotic infusions once the dura is opened and allow the patient to awaken.
Corticography
EEG recording is performed directly from the cortical surface using interictal spiking to
identify the seizure focus and delineate the extent of the planned resection. For this, the
patient should be awake.
Functional mapping
With the patient should be awake and alert, motor and sensory cortex, language and
memory areas will be identified. Seizures may occur and are usually self-limiting,
however, may require treatment with iced saline to the brain or thiopental/propofol.
Cortical resection
During this period, the surgeon may request that the patient remain awake. Resume the
propofol and narcotics infusion after verifying with surgeon.
Post resection EEG
This is done to ensure that the seizure focus has been successfully resected. The
patient should be awake. If the patient was sedated, coordinate with the surgical team
to have the patient awake when needed.
Closure
The patient will need to be sedated again as the dura/bone flap and scalp are closed.
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Basic Lateral Position for awake craniotomies
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NEUROPHYSIOLOGIC MONITORING
Objectives:
Know basic implications of changes induced by either anesthesia or surgery in
the electroencephalogram (EEG)/processed EEG (pEEG) and evoked potentials.
Electroencephalogram
 Understand basic wave patterns and concepts of frequency and amplitude
 Understand typical changes in EEG patterns with induction of anesthesia
as well as changes associated with deepening of anesthesia
 Understand EEG changes associated with ischemia - mild, moderate and
severe
Transcranial doppler (TCD) monitoring
 Know theoretical basis for TCD monitoring
 Know indications and use for TCD monitoring
 Know limitations of TCD monitoring
Evoked potentials
 Have a general concept about the generators of brainstem auditory
evoked responses, somatosensory evoked responses, motor evoked
potentials and electromyography.
 Understand basic evoked potentials descriptors- latency and amplitude
 Know effects of general anesthetic agents (both inhalation agents and
intravenous agents) on evoked potentials
 Know the significance of non-pharmacologically induced changes in
evoked responses during surgery
lntracranial pressure monitoring
 Know indications and complications associated with ICP monitoring
 Understand advantages and disadvantages of commonly used ICP
monitoring techniques
EEG monitoring can be a useful supplement to surgery when seizures need to be
identified (see “seizure surgery”), when the general state of cerebral metabolism needs
monitoring or when cerebral ischemia can occur. EEG is a standard of care in many
institutions for carotid endarterectomy. There are no special anesthesia requirements
for EEG, but each agent may cause slightly different patterns. A constant level of
anesthesia will better allow one see EEG changes representative of ischemia. Certain
anesthetics need to be avoided if seizure monitoring is desired (especially inhalational
and benzodiazepam).
The EEG is generated by synaptic potentials in the surface pyramidal cell layer of the
cortex and hence only monitors the 20% of the brain on the cerebral surface. The EEG
is monitored by applying surface electrodes; one electrode is used for all channels and
is called a ground. This ground electrode can be placed anywhere on the head and is
often placed somewhere on the midline.
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Each channel of the EEG uses 2 electrodes. The EEG machine simply amplifies the
difference between these two electrodes. The activity seen represents the area of
brain within 2-3 cm of each electrode.
Examining the raw, single channel EEG one can see the alpha rhythm of a lightly
anesthetized individual. This is a rhythmical regular wave of 8-12 cycles per second. A
faster, disorganized Beta (> 12 Hz) rhythm is seen when awakening. Slower theta
waves (4-8 Hz) are seen with deep inhalational or moderate dose narcotic anesthe sia.
Slow Delta (< 4 Hz) waves may be deep anesthesia, or may be ischemia if low
amplitude. Deep anesthesia suppression can be seen as so called “burst suppression”.
Here bursts of EEG activity are alternated by regions of inactivity. At this point near
maximal metabolic suppression (40-50%) is produced by anesthesia. Deeper metabolic
suppression requires hypothermia and is signalled by a flat line. Under special
conditions “spike and wave” seizure activity may be seen representative of seizures.
Although one EEG channel is useful to examine the general state of the brain, 2 or
more symmetrical channels are best used when examining for vascular ischemia. For
example, when a specific vascular territory is at risk, one channel should be placed over
the area at risk (such as the parietal cortex of the middle cerebral artery during a carotid
endarterectomy) and a second channel placed in an area not at risk (such as the other
side of the head). Thus when both channels change, the drop is a global event (e.g.,
deep anesthesia or hypotension) with a unilateral event signalling a vascular event.
For CEA, a minimum of 2 channels are recommended with the electrodes placed
over the left and right parietal cortices (the middle cerebral artery territory).
Note that deep anesthesia and ischemia are both shown on the EEG as slow waves
and eventually flat EEG. Thus the EEG must be interpreted in the context of the rest of
the surgery, physiology and anesthesia.
TRANSCRANIAL DOPPLER MONITORING (TCD)
TCD is discussed below because although not clinically relevant at this institution, it is
used at some institution. The basic concept and its application are addressed below.
The transcranial Doppler (TCD) uses the Doppler shift of sound waves reflected off
moving red blood cells to measure blood flow velocity in the basal cerebral arteries
(most commonly, the middle cerebral artery). The waveform resembles an arterial
pulse waveform, quantified into systolic, mean and diastolic flow velocities and
pulsatility index. When interpreting TCD values, an assumption is made that changes in
blood flow velocity reflect changes in cortical CBF. However, this assumption is true
only as long as the diameter of the conducting cerebral arteries does not change and
the measurement angle of the Doppler probe (angle of isonation) remains constant. It is
also important to note that technically satisfactory recordings cannot be obtained in all
patients.
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A major use of TCD in neuroanesthesia has been during carotid endarterectomy (CEA)
as an indicator of the adequacy of cerebral blood flow, and for detection of vasospasm
following subarachnoid hemorrhage (SAH). During CEA, TCD is used to detect low CBF
during the time of carotid cross clamping, which indicates the need for shunt placement.
If a reduction in mean cerebral artery (MCA) velocity to 40% or less of pre-clamp values
is seen, our neurosurgeons place a shunt. TCD is also useful to detect cerebral emboli
(both particulate and air), which are most commonly seen at the time the carotid clamp
is removed. One additional use of TCD during CEA is detection of cerebral hyperemia,
which is associated with a large increase in MCA velocity (greater than 1 00%) after the
carotid clamp is removed. This is a valuable indicator of the importance of avoiding
emergence and postoperative hypertension, to prevent the development of
postoperative headache, seizures and cerebral hemorrhage.
In the intensive care unit (ICU), the TCD is useful for detection and documentation of
the severity of vasospam after SAH. As the diameter of the arterial lumen decreases
with vasospasm, the velocity of blood flowing through the narrowed vessel must
increase if flow is to be maintained. Vasospasm is diagnosed by mean MCA velocity of
> 120 cm/ sec and a MCA/ICA ratio (Lindegaard Ratio) of > 3.
Although not part of the criteria for brain death, a characteristic TCD pattern is seen in
patients who are clinically brain dead. Blood moves forward during systole, which is
seen on the TCD as a short systolic inflow of blood. However, because blood flow has
ceased in the microvascular bed, this is followed by flow reversal during diastole,
associated with the exit of blood from the cranium.
EVOKED POTENTIALS
Evoked potentials (EP) can be used to examine specific neural tracts. To allow
optimal EP monitoring, the anesthetic agents are important, but more importantly, the
level of anesthesia must be constant so that changes noted on evoked potentials are
not confused with the effect of changing anesthetic depth.
In general, evoked potentials are measured by placing recording electrodes so that
small electrical “potentials” can be seen when they are “evoked” (elicited) by stimulating
the nervous system. These electrical events are like the P, Q, R, S, T waves in the EKG
and represent the electrical events that follow activation of a nervous system pathway.
Unfortunately, differing from the EKG, these electrical signals are so small that several
hundred to several thousand must be recorded and averaged so that background noise
is removed. Hence a sophisticated recording device and a technician are required.
Brainstem Auditory Evoked Responses (BAER) or Auditory Brainstem Responses
(ABR) are produced by stimulating the ear by sound “pips” or clicks using earphones.
There are 5 recognizable waves in the first 10 milliseconds which represent the
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electrical response of the eighth cranial nerve, lower and upper brainstem. These are
useful in ear surgery (where the cochlea is at risk) or in posterior fossa surgery on the
brainstem (such as acoustic neuroma). Fortunately there are no anesthesia restrictions
for this technique. It should be noted that the auditory cortex can be monitored by
recording the potentials over the auditory sensory area (temporal-parietal cortex) after
ear stimulation (midlatency auditory response). The anesthetic requirements are similar
to the SSEP (i.e., somewhat restrictive).
SomatoSensory Evoked Potentials (SSEP) are produced by electrical signals placed
over major peripheral nerves. Similar to a neuromuscular block stimulator these
depolarize the nerve causing a muscle twitch (equivalent to tetanus) and initiate a series
of recordable sensory signals traversing up the peripheral nerve, plexus (lumbar or
brachial), spinal cord, brainstem and sensory cortex. Electrodes can be placed at
various locations over these structures to record the signal. Neuroanatomically, the
signals appear to correlate best with neural pathways of proprioception and vibration
(joint sense). Median nerve, ulnar nerve, posterior tibial nerve and common peroneal
nerve are most commonly used. However, because the cortical SSEP is produced by
the sensory cortex, it can be used for some cortical surgery where the sensory cortex is
placed at risk (such as vascular surgery). All inhalational agents (including N 2O) have
been shown to depress cortical SSEP with minimal effects on brainstem and more
caudal potentials (e.g., peripheral nerve signals are very resistent). Hence if the cortical
signals are desired (as they almost always are) a narcotic based anesthetic with
supplemental low dose inhalational anesthetic is probably the best initial anesthetic. If
signals are too small, then a total intravenous technique may be best. On rare
occasions, the SSEP may not be recordable. Note that muscle relaxants do not interfere
with sensory evoked potentials. However, it is useful with the SSEP to see the hand or
foot twitch to verify proper nerve stimulation therefore moderate neuromuscular
blockade is acceptable (TOF 2/4 or greater) unless contraindicated by the surgical
procedure or some other form of monitoring such as electromyography (EMG). At this
institution, EMG is almost always performed as part of neuromonitoring.
Visual Evoked Potentials (VEP) are recorded over the occipital cortex after stimulation
of the eyes by light flashes. These are extremely sensitive to anesthesia. VEP has
generally lost favor as a monitor. VEP are typically performed on patients with multiple
sclerosis on an outpatient basis with no anesthesia personnel involvement.
Motor evoked potentials (MEP) differ from sensory evoked potentials in that
they attempt to monitor motor tracts. MEP can be produced by transcranial
stimulation from magnets (tcMMEP) with the potentials recorded over the spinal
cord or by high voltage shocks (tcEMEP) through electrodes placed on the scalp
with potentials recorded peripherally. An alternate to cranial stimulation is spinal
cord stimulation via epidural electrodes (scEMEP) or by electrodes placed in or
on the vertebral bodies (neurogenic MEP- nMEP). However, since the entire cord
is stimulated, criticism is raised about monitoring not being pure motor tracts.
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scEMEP and nMEP are both very resistent to anesthetics and may require
muscle relaxation to remove muscle interference. At this institution, tcEMEP is
routinely used.
Electromyogram (EMG) measures the electrical activity of muscles at rest and
during contraction. It is usually achieved via intramuscular electrode placement.
This technique allows for observation of neurotoxic discharges with nerve
irritation. This technique is not sensitive to volatile anesthetics but is sensitive to
neuromuscular blockade.
Anesthetic management
EEG only (moderately sensitive to volatile anesthetic insensitive to neuromuscular
blockade)
 Induction as usual
 Balanced Maintenance (≤1 MAC)with propofol, opioids and neuromuscular
blockade as needed
BAER only ( insensitive to volatile anesthetic or neuromuscular blockade)
 Induction as usual
 Maintenance as usual
SSEP only (sensitive to volatile anesthetic insensitive to neuromuscular blockade)
 Induction as usual
 Balanced Maintenance ( ½-1 MAC, ketamine, propofol and/or dexmedetomidine)
 Opioids and neuromuscular blockade as needed
MEP (very sensitive to volatile anesthetic & neuromuscular blockade)
 Induction as usual (neuromuscular blockade as needed for induction)
 TIVA – Opioids , propofol and ketamine. (Note:Use of dexmedetomidine not
recommended)
When EMG is used in combination with any of the techniques above, neuromuscular
blockade should be avoided. Keep in mind that although some neuromonitoring
techniques are insensitive to neuromuscular blockade, the procedure itself may
preclude use of neuromuscular blocking agents.
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