NEUROANESTHESIA
| NEUROANESTHESIA: CHANGING PRACTICES— John C. Drummond, MD, Professor of Anesthesiology, University
of California, San Diego, School of Medicine, and Staff Anesthesiologist, Veterans Affairs Medical Center, San Diego
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| Intracranial aneurysms: no longer performed exclusively in operating room (OR); predictions are that ≈80% ultimately
will be managed by interventional team rather than open surgery; anesthesia involved in many interventional
procedures
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 | Current management: platinum coil coated with thrombogenic material, deployed inside aneurysm; produces thrombosis,
clot forms inside dome of cavity, and aneurysm resolved; however, when aneurysm has wide neck, coils do not
stay within dome of aneurysm; secondly, even though thrombosis may occur within much of aneurysm, residual neck
and some remaining thin tissue not uncommon
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| International Subarachnoid Aneurysm Trial (ISAT): compared clipping with coiling; randomized 2000 patients to
interventional or surgical management; end points at 1 yr were death or dependency on others for care; statistically
significant difference in favor of coiling (23.5% vs 30.9%); bias against clipping group because of experience
of surgeons; rebleeding rate in coiling group 2 per 1276 patient-years
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| Management of wide-neck aneurysm: involves deploying stent-like structures to retain coil within dome of aneurysm
(even basilar apex aneurysm can be assisted with stenting devices); in chin-down position, radiologist able
to see supratentorial space, but bones obscure much of vasculature of posterior fossa; subtraction technique allows
further visualization; however, if patient moves, subtraction mask useless
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| Presence of anesthesia provider: necessary to provide general anesthesia (GA) and keep patient immobile; radiologists
respect physiology management skills (eg, volume loading and induced hypertension to assure collateral
flow; administer protamine and manage complications associated with its administration intelligently in event of
hemorrhagic crisis)
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| Pharmacologic protection of brain in subarachnoid hemorrhage: exact cause of vasospasm still unclear;
involves breakdown product of oxygenated hemoglobin (“cakes” vessels of Circle of Willis at base of brain); crude
mechanical therapy known as “triple H” (pharmacologically induced hypertension, hypervolemia, and hemodilution
[to lower hematocrit]) aimed at forcing blood through narrowed vessel by raising driving pressure and thinning
blood, remains cornerstone of treatment; oral nimodipine standard part of therapy for ≥21 days after ictus; recent
randomized trials demonstrated improvements in vasospasm, delayed ischemic deficit, outcome, and mortality as result
of administration of endothelin antagonists, magnesium, and statins
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| Carotid endarterectomy (CEA): some procedures moved from OR to interventional suites; involves transfemoral
access in patient receiving monitored anesthesia care (MAC)-type anesthetic; balloon deployed across site of
stenosis, then inflated; second passage deploys stent device (requires pressure to dilate; endothelial cells grow
relatively rapidly across lattice); endothelialized surface follows in 36 to 48 hr; balloon ≈2 cm in length; rated to
rupture at ≈14 atm (10 atm standard inflation pressure across aneurysm; ambient pressure 760 mm Hg); ensure
transthoracic pacemaker present with relevant pads available; in early studies, stroke rate related to embolization
of debris; subsequent generation used distal protection devices; current devices use seine net passed through center
of balloon cannula; deployed distally; catches debris; cinched shut and pulled out femoral artery with debris;
Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy (SAPPHIRE) trial demonstrated
“noninferiority” of stenting vs open operation; equivalent risk for stroke and death at 30 days; fewer revascularizations
at 1 yr in stenting group; Carotid Revascularization Endarterectomy vs Stent Trial (CREST)
reportedly observed that stroke rate rises as patient’s age increases (using distal embolization device); interim
suspicion that older patient more likely to have atheromatous debris in aortic root
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| Carotid angioplasty/stenting: usually transfemoral approach; occasionally transcarotid; usually MAC approach (neurologic
examination; transcarotid typically performed using GA); 2 stages with bradycardia risk (dilatation and
stenting)
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| Prevent or treat bradycardia: independent arterial line; atropine before dilatation may produce tachycardia; glycopyrrolate
pretreatment to increase heart rate to 75 or 80 beats per min; external pacer available
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| Heparin: to maintain activated clotting time (ACT) at ≈250 sec (requires ≈5000 U; ≈1000 U/hr)
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| Regional vs general anesthesia
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| Advantages claimed for regional anesthesia: speaker cannot accept quality of science underlying most claims (except
fewer unnecessary shunts)
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| Local/regional techniques for CEA: “straight” local infiltration; deep cervical plexus block; superficial cervical plexus
block (reportedly as effective as deep cervical plexus block); interscalene block; cervical epidural; reported advantages
of laryngeal mask airway (LMA) include smoother induction and smoother emergence; characteristically performed
using positive-pressure ventilation (bubbling of lubricant jelly placed down nasogastric tube lumen used to
confirm placement of LMA); when using neurologic signs as indication for shunting, 3 min sufficient to test occlusion;
some patients require conversion to GA
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| Neuronavigation: few anesthetic considerations; magnetic resonance imaging (MRI) results fed to neuronavigation
system, which calculates physical relationship between intracranial space and bones of face; patient placed into head
frame; surgeon begins by shining laser light on facial bones (do not tape eyes until afterwards); laser light reflects up to
neuronavigation system, then back down to reflecting surfaces which are in fixed relationship to facial bones; localizing
surgical instruments similarly have reflecting surfaces; surgeon places device on skull, and neuronavigation system indicates
location of instrument relative to lesion of interest; mannitol administration and relatively aggressive hyperventilation
less likely used so that brain geometry remains constant
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| Neuroendoscopy: variety of lesions, particularly within third ventricle (sometimes vascular lesions; most often
colloid cysts), that can be approached without craniotomy; enter through frontal or occipital horns into ventricle,
and resect with endoscopy; requires 2 ports; similar to knee arthroscopy; important to be vigilant for hemodynamic
changes (hypertension and bradycardia most ominous); most important anesthetic consideration to warn surgeon of
blockage of effluent pathway as early as possible
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| Hypothermia: in laboratory, 2° to 4° temperature reductions shown to be dramatically protective in animal experimental
situations; study by Todd and colleagues of mild hypothermia during surgery for intracranial aneurysm
found “absolutely no difference in outcome”; Clifton study of brain-injured patients found that those <45 yr of age,
with temperature on hospital arrival <35°C, and randomized to control group (as compared to those randomized to
“warm group”) showed improved outcome; “today hypothermia is not part of the management of head injury”
(may, however, be useful following cardiac arrest; unconscious adult patient, whose circulation has been restored,
and who has had witnessed cardiac arrest, should be cooled for 12 to 24 hr when initial rhythm was ventricular fibrillation
[VF; excludes asystolic patient])
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| CO2 management and hyperventilation: concerns about vasoconstriction; may lead to ischemia; considerable
restraint employed in use of hyperventilation; however, still used to treat intracranial crisis
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| CAN WE PROTECT THE BRAIN ?—Elizabeth H. Sinz, MD, Associate Professor of Anesthesiology, Critical Care
Medicine, and Neurosurgery, and Director, Simulation and Cognitive Science Laboratory, Pennsylvania State University
College of Medicine, Hershey
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| Summary of Hershey Medical Center 2005 neuromonitoring data: 641 cases used neuromonitoring; intraoperative
changes reported in 28 cases (≈4%; most occurred in complex spine cases and neuroradiology cases)
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| Somatosensory evoked potentials (SSEP): used to monitor integrity of nerve pathways, mostly sensory, from periphery
to cortex; routine for surgical procedures involving spinal column with risk to spinal cord and carotid endarterectomy;
allow detection of subcortical ischemia; necessary to average numerous signals to eliminate noise;
multiple reports of false-negative outcomes; ≈28% of neurologic complications not detected by SSEP monitoring
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| Reasons SSEP monitoring fails: lesion lies outside tract being assessed; lesion not at level being monitored; preexisting
neurologic defect compromising quality of recordings; technical problems during surgery; deficit may occur
postoperatively; slow onset of deficit, making it irreversible once detected; anesthetic effects
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| Stagnara wake-up test: drawbacks include loss of lines or accidental extubation, patient recall, slow, not continuous,
and only works in cooperative patient
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| Motor-evoked recordings: stimulation across motor cortex; recorded distally at muscle; also stimulate along spinal
cord and peripheral nervous system; assess motor pathways from cortex to distal muscle; known as transcranial
motor-evoked potentials (TceMEP); administer small electrical current; needles placed in scalp; responses
“all or nothing”; checked at time of surgical manipulation; other types of mapping, together with MEP, also possible
(particularly useful with spinal cord tumors)
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| Benefits of TceMEP: instant results; can be obtained in patients where SSEP cannot; directly measures corticospinal
pathway; more sensitive to ischemia than SSEP; less sensitive to electrical noise
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| Problems with TceMEP: paralytic-sensitive; movement; anesthetic-sensitive; contraindicated in seizures (particularly
with direct brain stimulation); requires bite block (patient can bite tongue); standardized paradigms for use
not fully agreed upon
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| Neuromonitoring and anesthesia: even low level of potent inhaled agent can have profound effect on MEP; compromised
signals make it more difficult to detect changes
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| Total intravenous anesthesia (TIVA) technique: commonly used combination includes dexmedetomidine, opioid,
and propofol; synergy between agents allows relatively low doses of each; initiate infusion when patient arrives
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| Balanced anesthesia technique: commonly used combination includes nitrous oxide, opioid, and propofol; some
signal loss possible
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| Propofol infusion kinetics: loss of response to skin incision in 50% of subjects (CP50) of propofol ≈4 µg/mL; CP50
wake up for propofol 1.4 µg/mL (without other suppressant agents); begin with bolus of 2.5 mg/kg, then give 200 µg/
kg per min for 10 min, followed by 166 µg/kg per min for 10 min, then 133 µg/kg per min; results in steady-state
level
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| Dexmedetomidine: creates synergy, allowing use of lower doses of propofol and opioid (speaker does not use
loading dose); clinical effect lasts ≈2 hr after discontinuation of infusion; no respiratory depression; can extubate
when other drug effects gone; side effects include hypotension and bradycardia (exaggerated at higher doses); dosage
range 0.3 to 0.7 µg/kg per hr
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| Narcotic infusions: any medium- to long-acting narcotic can be used (eg, fentanyl, sufentanil); remifentanil best
for cases of high intensity without postoperative pain; “opioids don’t make people sleep”; difficult to “get the patient
back breathing” safely until head pins removed
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| Ketamine: increases cerebral blood flow and cerebral metabolic rate; potentially increases intracranial pressure; potential
protective effects in brain injury
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| Emergence: anxiety-producing for many (head pins; rapid emergence; hemodynamic stability; coughing; neurologic
examination; intensive care unit [ICU]); goal is “smooth transition from asleep to awake”; time of emergence
should be predicted and shared with neurosurgical team
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| Technique: muscle-relaxed—may be initiated at end of case; titrate antihypertensives as anesthetics dissipate; give
muscle relaxant reversal agent after head pins removed; not muscle-relaxed—if patient coughs on endo-tracheal
tube, trade for LMA near end of procedure
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| Alternate-site anesthesia: therapeutic procedures (eg, aneurysm); unfamiliar and “hostile” environment of radiology;
useful for neuromonitoring
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| Awake craniotomy: speaker’s technique—propofol titrated to sedation (20 to 50 µg/kg per min); dexmedetomidine
(“hold still” drug); remifentanil titrated to respiratory rate; must be positioned carefully (6- to 12-hr procedure);
most painful part of case placing Foley catheter and local anesthetic injections
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| Asleep-awake-asleep technique: remain intubated—discontinue inhalation agent; continue opioid and muscle
relaxant; extubated—begin case as GA with, eg, LMA; discontinue anesthetic agents; remove airway as patient
emerges; replace airway when testing complete
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Educational Objectives
| The goal of this program is to educate the listener about changing practices in neuroanesthesia and protecting the patient
during anesthesia for neurosurgery cases. After hearing and assimilating this program, the participant will be
better able to:
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| 1. Review anesthetic management of intracranial aneurysms and carotid endarterectomy.
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| 2. Discuss neuronavigation, neuroendoscopy, and management of hypothermia in neurosurgery.
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| 3. Demonstrate how to plan a safe anesthetic for cases involving neuromonitoring or alternative-site locations.
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| 4. Communicate effectively with neurophysiologists and neurosurgeons about anesthetic effects.
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| 5. Execute a smooth emergence from anesthesia in neurosurgery cases.
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Discussed on This Program
Atropine sulfate (several trade names)
Dexmedetomidine HCl [Precedex]
Fentanyl citrate [Sublimaze]
Glycopyrrolate [Robinul, Robinul Forte]
Heparin sodium injection
Hydromorphone HCl [Dilaudid, Dilaudid-5, Dilaudid-HP, Palladone]
Ketamine HCl [Ketalar]
Nimodipine [Nimotop]
Nitrous oxide (N2 O)
Propofol [Diprivan]
Protamine sulfate
Remifentanil HCl [Ultiva]
Sevoflurane [Ultane]
Sufentanil citrate [Sufenta]
Suggested Reading
Awad IA et al: Clinical vasospasm after subarachnoid hemorrhage: response to hypervolemic hemodilution and arterial
hypertension. Stroke 18:365, 1987; Clifton GL et al: Lack of effect of induction of hypothermia after acute
brain injury. N Engl J Med 344:556, 2001; Dawson EG et al: Spinal cord monitoring. Results of the Scoliosis Research
Society and the European Spinal Deformity Society survey. Spine 16:S361, 1991; Drummond JC: Changing
practices in neuroanaesthesia. Can J Anaesth 37:Slxxxix, 1990; Drummond JC: Deliberate hypotension for
intracranial aneurysm surgery: changing practices. Can J Anaesth 38:935, 1991; EVA-3S Investigators: Endarterectomy
vs. Angioplasty in Patients with Symptomatic Severe Carotid Stenosis (EVA-3S) Trial. Cerebrovasc Dis
18:62, 2004; Hobson RW 2nd et al: Carotid artery stenting is associated with increased complications in octogenarians:
30-day stroke and death rates in the CREST lead-in phase. J Vasc Surg 40:1106, 2004; Hobson RW 2nd
et al: CREST: carotid revascularization endarterectomy versus stent trial. Cardiovasc Surg 5:457, 1997; Hobson
RW 2nd et al: Organizing the Carotid Revascularization Endarterectomy versus Stenting Trial (CREST): National
Institutes of Health, Health Care Financing Administration, and industry funding. Curr Control Trials Cardiovasc
Med 2:160, 2001; Hobson RW 2nd: CREST (Carotid Revascularization Endarterectomy versus Stent Trial): background,
design, and current status. Semin Vasc Surg 13:139, 2000; Hobson RW 2nd: Update on the Carotid Revascularization
Endarterectomy versus Stent Trial (CREST) protocol. J Am Coll Surg 194:S9, 2002; Kofke WA et al:
The neuropathologic effects in rats and neurometabolic effects in humans of large-dose remifentanil. Anesth Analg
94:1229, 2002; Levy WJ: Spinal evoked potentials from the motor tracts. J Neurosurg 58:38, 1983; Molyneux A
et al: International Subarachnoid Aneurysm Trial (ISAT) of neurosurgical clipping versus endovascular coiling in
2143 patients with ruptured intracranial aneurysms: a randomised trial. Lancet 360:1267, 2002; Nolan JP et al:
Therapeutic hypothermia after cardiac arrest: an advisory statement by the advanced life support task force of the International
Liaison Committee on Resuscitation. Circulation 108:118, 2003; Pandit JJ et al: A comparison of superficial
versus combined (superficial and deep) cervical plexus block for carotid endarterectomy: a prospective,
randomized study. Anesth Analg 91:781, 2000; Pickard JD et al: Effect of oral nimodipine on cerebral infarction
and outcome after subarachnoid haemorrhage: British aneurysm nimodipine trial. BMJ 298:636, 1989; Ringleb PA
et al: The Stent-Supported Percutaneous Angioplasty of the Carotid Artery vs Endarterectomy Trial. Cerebrovasc
Dis 18:66, 2004; Sinz EH et al: Inducible nitric oxide synthase is an endogenous neuroprotectant after traumatic
brain injury in rats and mice. J Clin Invest 104:647, 1999; Sinz EH et al: Phenytoin, midazolam, and naloxone protect
against fentanyl-induced brain damage in rats. Anesth Analg 91:1443, 2000; Todd MM et al: Mild intraoperative
hypothermia during surgery for intracranial aneurysm. N Engl J Med 352:135, 2005; van den Bergh WM et
al: Magnesium sulfate in aneurysmal subarachnoid hemorrhage: a randomized controlled trial. Stroke 36:1011, 2005;
Yadav JS et al: Protected carotid-artery stenting versus endarterectomy in high-risk patients. N Engl J Med
351:1493, 2004; Zornow MH et al: Intraoperative somatosensory evoked responses recorded during onset of the
anterior spinal artery syndrome. J Clin Monit 5:243, 1989.
Faculty Disclosure
In adherence to ACCME guidelines, the Audio-Digest Foundation requests all lecturers to disclose any significant financial
relationship with the manufacturer or provider of any commercial product or service discussed. For this issue,
the faculty reported nothing to disclose.
Dr. Drummond was recorded at the Annual Meeting and Anesthesiology Review Course, jointly presented May 18-
21, 2006, by the California Society of Anesthesiologists and University of California, San Diego, School of Medicine,
and held in Rancho Mirage, CA; Dr. Sinz, at the 56th Annual Postgraduate Symposium on Anesthesiology, presented
March 31, April 1-2, 2006, by the University of Kansas Medical Center Department of Anesthesiology and
University of Kansas Continuing Education, and held in Kansas City, MO. The Audio-Digest Foundation thanks the
speakers and the sponsors for their cooperation in the production of this program.
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