(BQ) Part 1 book “Fundamentals of neuroanesthesia - A physiologic approach to clinical practice” has contents: Central nervous system anatomy, therapeutic control of brain volume, cerebral ischemia and neuroprotection, awake craniotomy, severe traumatic brain injury,… and other contents.
F UN DA M E N TA L S O F N E UR OA N E ST HE S I A This page intentionally left blank FUNDAMENTALS OF NEUROANESTHESIA A PHYSIOLOGIC APPROACH TO CLINICAL PR ACTICE EDITED BY Keith J Ruskin, MD PROFESSOR OF ANESTHESIOLOGY AND NEUROSURGERY DIRECTOR, NEUROANESTHESIA D E PA RTM E N T O F A N E ST HE SI O LO GY YA L E S C H O O L O F M E D I C IN E N E W H AV E N , C O N N E C T I C U T Stanley H Rosenbaum, MD P R O F E S S O R O F A N E S T H E S I O L O G Y, M E D I C I N E AND SURGERY VICE CHAIR , ACADEMIC AFFAIR S D I R E C T O R , P E R I O P E R AT I V E A N D A D U LT A N E S T H E S I A D E PA RTM E N T O F A N E ST HE SI O LO GY YA L E S C H O O L O F M E D I C IN E N E W H AV E N , C O N N E C T I C U T Ira J. Rampil, MD PROFESSOR OF ANESTHESIOLOGY AND NEUROLOGIC SURGERY S TAT E U N I V E R S I T Y O F N E W Y O R K AT S T O N Y B R O O K STONY BROOK, NEW YORK Oxford University Press is a department of the University of Oxford It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With offices in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Oxford is a registered trademark of Oxford University Press in the UK and certain other countries Published in the United States of America by Oxford University Press 198 Madison Avenue, New York, NY 10016 © Oxford University Press 2014 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, by license, or under terms agreed with the appropriate reproduction rights organization Inquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this work in any other form and you must impose this same condition on any acquirer Library of Congress Cataloging-in-Publication Data Fundamentals of neuroanesthesia : a physiologic approach to clinical practice / edited by Keith J Ruskin, Stanley H Rosenbaum, Ira J Rampil p ; cm Includes bibliographical references and index ISBN 978–0–19–975598–1 (alk paper) I Ruskin, Keith.— II Rosenbaum, Stanley H.— III Rampil, Ira J [DNLM: Anesthesia.— Neurosurgical Procedures WO 200] RD87.3.N47 617.9′6748—dc23 2013009160 This material is not intended to be, and should not be considered, a substitute for medical or other professional advice Treatment for the conditions described in this material is highly dependent on the individual circumstances And, while this material is designed to offer accurate information with respect to the subject matter covered and to be current as of the time it was written, research and knowledge about medical and health issues is constantly evolving and dose schedules for medications are being revised continually, with new side effects recognized and accounted for regularly Readers must therefore always check the product information and clinical procedures with the most up-to-date published product information and data sheets provided by the manufacturers and the most recent codes of conduct and safety regulation The publisher and the authors make no representations or warranties to readers, express or implied, as to the accuracy or completeness of this material Without limiting the foregoing, the publisher and the authors make no representations or warranties as to the accuracy or efficacy of the drug dosages mentioned in the material The authors and the publisher not accept, and expressly disclaim, any responsibility for any liability, loss or risk that may be claimed or incurred as a consequence of the use and/or application of any of the contents of this material Printed in the United States of America on acid-free paper CONTENTS Preface Acknowledgments Contributors vii ix xi Central Nervous System Anatomy Maxwell S Laurans, Brooke Albright, and Ryan A Grant 16 Awake Craniotomy John Ard 201 17 Anesthesia for Posterior Fossa Surgery Rashmi N Mueller 209 223 Therapeutic Control of Brain Volume Leslie C Jameson 16 18 Surgery for Epilepsy Lorenz G Theiler, Robyn S Weisman, and Thomas M Fuhrman 25 19 Severe Traumatic Brain Injury Ramachandran Ramani 236 Monitoring Cerebral Blood Flow and Metabolism Peter D Le Roux and Arthur M. Lam 50 20 Spinal Surgery Maria Bustillo 246 Neuromonitoring Basics: Optimizing the Anesthetic Stacie Deiner 61 21 Interventional Neurovascular Surgery Ketan R. Bulsara and Keith J Ruskin 256 Cerebral Ischemia and Neuroprotection James G. Hecker Neuroimaging Techniques Ramachandran Ramani 77 Pharmacology of Intravenous Sedative—Hypnotic Agents Joshua H. Atkins and Jessica Dworet 23 Positioning for Neurosurgery Richard B Silverman 90 Pharmacology of Opioids Joshua H. Atkins and Jessica Dworet 109 Inhaled Anesthetics Ariane Rossi and Luzius A Steiner 120 10 Neuromuscular Blockade in the Patient with Neurologic Disease Anup Pamnani and Vinod Malhotra 22 Carotid Endarterectomy and Carotid Artery Bypass Colleen M. Moran and Christoph N Seubert 24 Airway Management for the Patient with an Unstable Cervical Spine Eric A. Harris 25 Neurosurgery in Pediatrics Craig D McClain and Sulpicio G Soriano 26 Acute Care Surgery in the Critically Ill Neurosurgical Patient Joss J. Thomas and Avinash B. Kumar 131 263 274 288 304 312 11 Fluid Management in the Neurosurgical Patient Markus Klimek and Thomas H. Ottens 142 12 Intracranial Tumors Ira J. Rampil and Stephen Probst 151 27 Occlusive Cerebrovascular Disease—Perioperative Management Ryan Hakimi, Jeremy S. Dority, and David L McDonagh 13 Pituitary and Neuroendocrine Surgery Patricia Fogarty-Mack 162 28 Neurosurgical Critical Care Ryan Hebert and Veronica Chiang 332 29 Ethical Considerations and Brain Death Adrian A. Maung and Stanley H Rosenbaum 347 30 Quality Management and Perioperative Safety Robert Lagasse 354 Index 365 14 Anesthesia for Skull Base and Neurovascular Surgery Jess Brallier 171 15 Anesthesia for Stereotactic Radiosurgery and Intraoperative Magnetic Resonance Imaging Armagan Dagal and Arthur M. Lam 185 v 319 This page intentionally left blank PREFACE The practice of neurosurgery has fundamentally changed over the past few years Recent accomplishments in neuroscience have provided increased opportunities to treat patients suffering from acute injuries to the nervous system, such as stroke, subarachnoid hemorrhage, and trauma For example, there have been many significant advances in the management of patients with both ischemic and hemorrhagic stroke Patients who would have once been considered to have an untreatable neurologic injury are now routinely being scheduled for interventional or surgical procedures, and a campaign has begun to educate the general public about the urgency of seeking treatment when they experience the symptoms of a stroke Until very recently, craniotomies, spinal instrumentation, and interventional procedures were limited to academic medical centers or tertiary care hospitals, but these procedures and many others are offered at community hospitals Anesthesiologists who work in these hospitals and who may not have subspecialty training are being asked to care for patients who require a neurosurgical procedure At the same time, emerging data suggest that the choices that we make in the operating room can improve the patient’s ultimate outcome A clear, concise textbook that covers the physiologic underpinnings of neurosurgical anesthesia while also providing practical information for the anesthesiologist who in general practice is a relatively new need Fundamentals of Neurosurgical Anesthesiology is written to help an anesthesia provider deal with planned neurosurgical procedures and the unforeseen emergencies that may occur during the perioperative period As we were developing the specifications for this book, we decided on two goals: This book should provide the critical information that all anesthesia providers should have when caring for the neurosurgical patient, and it should contain a thorough and user-friendly review of the anesthetic management of neurosurgical patients The first part of the book reviews physiology and pharmacology from the perspective of the neurosurgical patient while the remaining chapters cover the aspects of subspecialty practice All chapters concentrate on the practical aspects of the practice of neurosurgical anesthesia The chapter authors are all recognized experts and are extensively published in the field of neurosurgical anesthesia Each contributor was asked to write a comprehensive discussion of the subject that also offered clear, practical recommendations for clinical practice In addition to references to basic science literature, an effort has been made to include references to clinical studies or review articles that will provide additional information This book would not have been possible without the support of many people The authors wish to thank Andrea Seils and Rebecca Suzan for patiently answering all of our questions and for their help with every aspect of this project We would also like to thank the many members of our departments who reviewed chapters and offered thoughtful advice Most importantly, we thank our families for their support and understanding while each of us spent many late nights in front of a computer or with printed chapters spread out around the house vi i This page intentionally left blank ACKNOWLEDGMENTS Last, we thank the residents and faculty of the Yale University School of Medicine, Department of Anesthesiology, for their critical reviews of the manuscript and their thoughtful comments This book would not have been possible without the help of many people The authors would first like to thank their families for their constant support We would like to thank our editors, Andrea Seils and Rebecca Suzan, for their advice and guidance We also thank our authors, who produced outstanding manuscripts and turned them in on time ix 83 Yang JJ, Li WY, Jil Q, et al Local anesthesia for functional endoscopic sinus surgery employing small volumes of epinephrine-containing solutions of lidocaine produces profound hypotension Acta Anestheiol Scand 2005;49:1471–1476 84 Yang J, Zheng J, Liu H, et al Epinephrine infiltration on nasal field causes significant hemodynamic changes: hypotension episode monitored by impedance-cardiography under general anesthesia J Pharm Pharmaceut Sci 2006;9:190–197 85 Yang J, Cheng H, Shang R , et al Hemodynamic changes due to infiltration of the scalp with epinephrine-containing lidocaine solution Neurosurg Anesthesiol 2007;19:31–37 86 Li W, Zhou Z , Ji J, et al Relatively light general anesthesia is more effective than fluid expansion in reducing the severity of epinephrine-induced hypotension during functional endoscopic sinus surgery Chin Med J 2007;120:1299–1302 87 Pepper J-P, Wadhwa AK, et al Cavernous carotid injury during functional endoscopic sinus surgery: case presentations and guidelines for optimal management Am J Rhinol 2007;109:105–109 170 • 88 Weidenbecher M, Huk WJ, Iro H Internal carotid artery injury during functional endoscopic sinus surgery and its management Eur Arch Otorhinolaryngol 2005;262:640–645 89 Gadhinglajkar SV, Sreedhar R , Bhattacharya RN Carotid artery injury during transsphenoidal resection of pituitary tumor: anesthesia perspective J Neurosurg Anesthesiol 2003;15:323–326 90 Paul M, Dueck M, Kampe S, et al Intracranial placement of a nasotracheal tube after transnasal trans-sphenoidal surgery Br J Anaesth 2003;91:601–604 91 McAdam D, Muro K , Suresh S The use of infraorbital nerve block for postoperative pain control after transsphenoidal hypophysectomy Reg Anesth Pain Med 2005;30:572–573 92 Higashizawa T, Koga Y Effect of infraorbital nerve block under general anesthesia on consumption of isoflurane and post operative pain in endoscopic endonasal maxillary sinus surgery J Anesth 2001;15: 136–138 93 Flynn BC, Nemergut EC Postoperative nausea and vomiting and pain after transphenoidal surgery: a review of 877 patients Anesth Analg 2006;103:162–167 C H A P T E R : P I T U I TA RY A N D N EU R O E N D O C R I N E S U R G E RY 14 ANESTHESIA FOR SKULL BASE AND NEUROVASCULAR SURGERY Jess Brallier S KU L L B A S E T U M O R S U R G E RY I N T RO D U C T I O N Skull base tumor surgery has changed significantly to become less invasive, moving from predominantly open procedures to endoscopic techniques Anesthetic techniques for these procedures have evolved to accommodate changes in surgical technique In the past, the anesthesiologist was most concerned with complications such as intraoperative blood loss and venous air embolism The focus has now shifted to providing an optimal, bloodless surgical field and using an anesthetic technique that permits the use of neurophysiologic monitoring Older, medically complicated patients are now candidates for skull base surgery, and management of these patients has become an important consideration Finally, patients are usually positioned with the head away from the anesthesiologist and his or her arms tucked at the side, complicating airway management and vascular access While surgery for skull base tumors has become less invasive, it is clear that anesthetic management of these patients requires a profound understanding of the procedure to ensure a smooth perioperative course P R E O P E R AT I V E M A NAG E M E N T Preoperative anesthetic evaluation should occur before the day of surgery in patients scheduled for an elective procedure This provides the opportunity for further work-up when necessary, minimizing the possibility of a delay on the day of surgery An understanding of the surgical procedure and of the tumor type are the primary preoperative considerations in patients presenting for endoscopic skull base surgery Each surgical procedure varies in terms of the neurovascular structures at risk, operative time, and potential for conversion to open surgery The most common skull base tumors include chondrosarcoma, chordoma, craniopharyngioma, meningioma, various pituitary tumors, and schwannoma These are often histologically benign lesions but require surgical treatment because they can cause nerve and tissue compression A thorough but focused history and physical examination is a critical component of the preoperative assessment Emphasis should be placed on evaluating the neurologic status, airway, cardiovascular system, pulmonary system, endocrine system, and fluid–electrolyte balance A careful history includes questions regarding the type and location of the lesion, preoperative deficits, and symptoms of elevated intracranial pressure (ICP) The patient should be questioned specifically about headache (often worse in the morning), vomiting, drowsiness, seizures, focal deficits, balance, vision changes, hearing loss, speech difficulties, bulbar symptoms, facial pain and paralysis, and personality changes If the preoperative assessment has been completed in advance, a careful review of the neurologic system should be performed on the day of surgery to screen for new symptoms and exacerbation of previous ones Airway Careful attention to airway management is imperative when anesthetizing patients for skull base tumor resection Patients with acromegaly caused by a pituitary tumor may be difficult to ventilate and to intubate because production of excess growth hormone causes soft tissue hypertrophy of the mouth, nose, tongue, turbinates, soft palate, and epiglottis and aryepiglottic folds Bony proliferation also results in prognathism and malocclusion Twenty-five percent of patients with a pituitary adenoma have a coexisting goiter, which may cause tracheal compression These patients may also have sleep apnea, which further complicates airway management [1] Patients should be asked about intubation history and, when available, prior anesthetic records reviewed Compared with other individuals, patients with elevated ICP have a low tolerance for apnea (apnea leads to increases in Paco2 to increases in cerebral blood flow [CBF] 171 to increases in ICP), highlighting the need for adequate ventilation and efficiency when securing the airway A complete airway examination should include the thyromental distance, mouth opening, and the Mallampati score The examination should also include head and neck movement and an evaluation of the patient’s ability to prognath If the history and physical examination suggest that airway management will be difficult, the anesthetic plan should include consideration of an awake intubation Emergency and adjunctive airway equipment should also be readily available Cardiac The cardiac evaluation is an essential part of any preoperative assessment and is particularly important in patients with certain types of skull base pathology Patients with acromegaly, for example, often present with myocardial hypertrophy, decreased cardiac performance, and increased cardiovascular mortality Cardiovascular complications cause a 5-fold increase in mortality in patients with Cushing’s disease compared with the normal population [2, 3] A preoperative cardiac evaluation is guided by the 2007 American College of Cardiology (ACC)/American Heart Association (AHA) algorithm for perioperative evaluation of the patient for noncardiac surgery and the patient’s symptoms, exercise tolerance, medical history, and tumor type Most patients presenting for endoscopic skull-based procedures present an intermediate risk Acromegaly and Cushing’s disease may increase the risk of structural and electrical cardiac pathophysiology leading to QT interval prolongation [4, 5] Ordering preoperative electrocardiograms in these patients may therefore be appropriate and further evaluation may be warranted in patients with functional adenomas Respiratory Preoperative respiratory considerations for the patient presenting for skull base tumor resection are essentially the same as those for individuals presenting for general surgery However, special attention must be given to patients with Cushing’s disease and acromegaly Patients with Cushing’s disease can present with moon facies and truncal obesity, potentially making airway management more difficult These patients are also at a higher risk for aspiration Acromegalic patients may also present with a number of respiratory challenges These patients have a high incidence of obstructive sleep apnea, which can complicate airway management and respiratory status throughout the perioperative period [6] Laboratory/Endocrine Evaluation Patients presenting for skull base tumor resection may have metabolic abnormalities as a result of their intracranial pathology Hyponatremia is frequently associated 172 • with tumors of the posterior pituitary Hypercalcemia may indicate a diagnosis of multiple endocrine neoplasia, type I. Pituitary adenomas generally present with symptoms of anterior pituitary hormone excess On the other hand, a subgroup of patients presenting for transsphenoidal surgery may have hypopituitarism and will receive hormone replacement therapy guided by laboratory studies Some patients may have adrenal insufficiency and stress dose steroid administration should also be considered in the perioperative period [7] Men with pituitary tumors and low testosterone levels are at risk for anemia [7] Basic laboratory studies should include a complete blood count, electrolytes, and a metabolic profile Coagulation studies are not usually necessary unless the patient has a known bleeding disorder Additional studies are guided by the tumor type and location In patients with a tumor of the anterior pituitary, laboratory tests should include a thyroid panel, serum levels of cortisol, adrenocorticotropic hormone, insulin-like growth factor 1, testosterone, luteinizing hormone, follicle-stimulating hormone, and prolactin [7] I N T R AO P E R AT I VE M A NAG E M E N T Induction Premedication should be avoided in patients presenting for skull base tumor surgery because administration of benzodiazepines or opioids may cause patients with elevated ICP to deteriorate rapidly Administering an antisialogogue such as glycopyrrolate is also prudent when anticipating a difficult airway Oversedation may cause hypoventilation and the resulting increase in Paco2 may increase CBF and exacerbate intracranial hypertension (HTN) If premedication is required (e.g., for a child or an extremely nervous patient) sedatives should be given by the anesthesiologist in a monitored setting American Society of Anesthesiologists (ASA) standard monitors (electrocardiogram, noninvasive blood pressure cuff, pulse oximetry, respiratory gas monitoring, and temperature) should be used in all patients Invasive monitoring of systemic arterial pressure should be considered in patients with skull base tumors, especially if intracranial HTN, significant heart disease, or other underlying comorbidities are present Although central venous pressure monitoring is not usually necessary for skull base surgery, it should be considered if large fluid shifts are suspected or large-bore peripheral intravenous catheters cannot be inserted The patient is usually positioned with his or her head away from the anesthesiologist with the arms tucked at the side This makes the airway, intravenous catheters, and intra-arterial catheter relatively inaccessible During induction, however, the patient should be positioned toward the anesthesia machine and personnel and turned away after the airway is secured Longer circuits, intravenous extensions, and sufficiently longer monitoring cables will also be required C H A P T E R : N EU R O VA S C U L A R S U R G E RY If a difficult airway is anticipated, then consideration should be given to an awake intubation, especially if problems with mask ventilation are anticipated Thorough topicalization should be performed with local anesthesia via atomization and combination of transtracheal and superior laryngeal nerve blocks Careful, sedation can also be administered using small amount of benzodiazepines such as midazolam or dexmedetomidine Dexmedetomidine, an α2-agonist, provides effective sedation without the hypoventilation that often accompanies other agents However, hypotension and bradycardia are common side effects of this drug, making careful titration essential If a difficult airway is anticipated (e.g., in an acromegalic patient), appropriately large oral airways, laryngeal mask airways (LMAs), and backup intubation devices (e.g., fiberoptic bronchoscope and/or video laryngoscopes) should be readily available [8] Should subglottic stenosis be anticipated, a range of endotracheal tube sizes should be ready and available If available, a second anesthesia provider can help with ventilation or intubation if the airway is lost during induction If the patient is at risk for aspiration (e.g., a morbidly obese patient with Cushing’s disease), a rapid sequence induction and extubation only when the patient is fully conscious may help to prevent aspiration The presence of cardiac disease, the projected length of surgery, the underlying pathology, and the presence or absence of intracranial HTN all guide the selection of an induction agent Propofol, etomidate, and thiopental decrease ICP by decreasing CBF, which makes them appropriate choices for induction of general anesthesia Propofol must be used discriminately in patients with cardiac disease due to the potential for precipitous decreases in blood pressure and myocardial depression Similarly, it must be carefully titrated in patients with intracranial HTN as sustained drops in blood pressure can lead to dangerous decreases in CPP Etomidate may be an appropriate alternative in many of these patients due to its ability to maintain hemodynamic stability However, it can cause adrenal suppression which might prove to be problematic in patients undergoing pituitary surgery Thiopental is no longer available in the United States and may be less appealing because of its longer half-life and its tendency to cause nausea and vomiting Etomidate may maintain hemodynamic stability in patients with decreased left ventricular function Ketamine should be avoided in patients with intracranial tumors because it increases ICP and CMRo2 The choice of a muscle relaxant at induction is guided by anticipated ability to manage the airway and whether the patient is considered to have a full stomach Should a rapid sequence induction be necessary, succinylcholine may be the most appropriate drug However, this drug should be administered with caution in patients who have known motor weakness or critical intracranial HTN due to its potential to precipitate a hyperkalemic arrest or further increase ICP, respectively The perceived risk of aspiration must be balanced against these risks If neurophysiologic monitoring is planned (somatosensory evoked potentials [SSEPs] or motor evoked potentials [MEPs]), a compatible anesthetic will have to be administered Inhalational agents cause a dose-dependent decrease and increase in evoked potential amplitude and latency, respectively This necessitates either decreasing the concentration of inhalational agent used or avoiding it entirely Alternatively, using a total intravenous anesthetic (TIVA) provides excellent anesthesia with negligible effect on neurophysiologic monitoring Similarly, when MEPs or electromyography (EMG) (in this case facial nerve monitoring) is to be used, muscle relaxants must be avoided once surgery has started [9, 10] However, using an intermediate-acting, nondepolarizing muscle relaxant such as rocuronium is usually appropriate for intubation and during line placement In any case, the anesthesiologist should discuss the intended use of neuromuscular blocking agents with the surgeon and the monitoring staff Maintenance The anesthetic plan should provide analgesia, amnesia, patient immobility, and hemodynamic stability while managing ICP and providing a “bloodless” surgical field Potent volatile anesthetics, intravenous anesthetics such as propofol, and narcotic techniques have all been used successfully Narcotics not cause cerebral vasodilation and may therefore provide an optimal surgical field Use of a narcotic with an ultra-short half-life, such as remifentanil, provides analgesia during the procedure and a rapid emergence after the surgery has ended Regardless of the chosen technique, the agents used should promote rapid awakening on surgical conclusion to allow for prompt, neurologic assessment Blood loss during surgery for skull base tumors results from injury to various vascular structures near the operative site Slow, intermittent venous bleeding is the most common cause of blood loss during these procedures However, more serious bleeding has resulted from injury to the internal carotid artery (ICA) and smaller vessels at the anterior skull base These complications have resulted in range from blindness, pituitary apoplexy, and stroke with permanent neurologic sequelae [11] Intraoperative bleeding tends to be more significant in patients with large tumors extending into the suprasellar region Endoscopic surgery is generally not associated with large amounts of blood loss or intraoperative fluid shifts However, should it occur it can become substantial as the surgeon operates and attempts to get hemostatic control in a very small field Adequate intravenous access in the form of two large-bore intravenous catheters should be obtained when risk of significant bleeding is present Fluid maintenance with an iso-osmotic crystalloid is generally adequate for intraoperative fluid replacement and usually osmotic dieresis is not necessary Iso-osmotic crystalloid solutions such as Plasma-Lyte or 0.9% normal saline are usually adequate for fluid replacement Care JESS BRALLIER • 173 must be taken not too administer large volumes of lactated Ringer’s (LR) solution as it is not truly iso-osmolar with respect to the plasma Consequently, the administration of large volumes of LR can result in decreased plasma osmolality and increased brain water content and ICP [12] Hypo-osmolar fluids and dextrose containing solutions should also be avoided for similar reasons [12] Diabetes insipidus (DI) is not uncommon in patients undergoing skull base surgery Factors found to increase the risk of postoperative DI include young age, male sex, large intrasellar mass, cerebrospinal fluid (CSF) leak, and resection of certain types of lesions (craniopharyngioma, Rathke-cleft cysts, and adrenocorticotropic hormone– secreting pituitary adenomas The onset of DI is usually heralded by large volumes of dilute urine in the absence of mannitol administration or other inciting factors A urine electrolyte panel will demonstrate hyponatremia and low specific gravity, while plasma sodium and specific gravity are elevated Should DI be detected intraoperatively, an intravenous infusion of aqueous ADH should be administered along with an isotonic crystalloid solution [13, 14] Serum sodium and plasma osmolality are measured at frequent, regular intervals and therapy altered as needed Postoperatively, DI is treated with subcutaneous injections of aqueous vasopressin One dose is often all that is required, but additional injections can be administered as needed Additionally, patients with an intact thirst mechanism should be allowed access to free water and intravenous fluids restricted [15] Postoperative pain is generally limited in these patients so large doses of long-acting opioids are usually not necessary A few studies have illustrated the benefits of specific nerve blocks during sinus surgery by reducing the amount of anesthetic and antihypertensives needed during surgery [16] Bilateral sphenopalatine ganglion blocks were shown in one study to decrease immediate postoperative opioid requirements and PACU stay [17] Such blocks are safe, effective, and easily administered at the start of the anesthetic Additionally, the utilization of nonopioid analgesics such as intravenous acetaminophen are also valuable postoperative adjuncts Emergence The anesthetic plan in most patients should permit the patient to awaken rapidly and be able to cooperate with a neurologic examination as soon as possible after surgery Barring any untoward intraoperative events, immediate extubation is usually appropriate in patients who not have extensive preoperative deficits The choice of sedatives and narcotics with relatively short half-lives is an important part in accomplishing this goal Straining and coughing during emergence may lead to venous bleeding or a cerebrospinal fluid leak The use of narcotics (either careful boluses of fentanyl or a longer-acting narcotic or a low-dose 174 • remifentanil infusion) will help the patient to be comfortable and alert Nausea and vomiting are very common in this patient population and its detrimental effects on ICP are well documented [7] Aggressive pharmacologic prophylaxis and treatment with 5-HT3 antagonists (e.g., ondansetron) should therefore be used Additional antiemetics may be administered as necessary, but droperidol should be avoided because of its sedative effects and the possibility of QT prolongation Due to patient positioning, the patient’s airway may not be immediately available to the anesthesia care provider until all surgical drapes and barriers have been removed Coordinating emergence and extubation with the surgical team are important determinants of successful emergence Ensuring that the patient is fully conscious and following commands prior to extubation is generally preferred However, deep extubation may be appropriate in carefully selected candidates If a previously neurologically intact patient fails to awaken and residual anesthetic agents have been excluded as a cause, immediate diagnostic imaging should be obtained to exclude the possibility of an intracranial hematoma P O S TO P E R AT I VE M A NAG E M E N T The level of care required in the postoperative period depends on the type of surgery performed, the potential for postoperative complications, and the patient’s medical comorbidities Most patients are transferred to the neurosurgical intensive care unit for postoperative management, but those having less extensive surgery may be admitted to the PACU and subsequently transferred to a medical-surgical floor Patients with a history of obstructive sleep apnea or other cardiopulmonary comorbidities, for example, should be transferred to a monitored bed in the immediate postoperative period Postoperative complications may occur soon after surgery or may be delayed Early complications include CSF leak, bleeding, DI, and visual loss Late complications include hormone deficits (particularly with transphenoidal pituitary surgery), prolonged problems with electrolyte and water balance, and meningitis [7, 18, 19] Headache is common after skull base surgery, and acute postoperative pain is usually treated with opioids and Nonsteroidal anti-inflammatory drugs (NSAIDs) However, if postoperative bleeding is a concern, avoiding NSAIDs and relying on short-acting opioids or intravenous acetaminophen may be prudent C O N C LUS I O NS : S KU L L BA S E T UMO R SU RG ERY Skull base tumor surgery has undergone significant evolution over the past 30 years The advent of minimally invasive surgical technique has decreased the incidence of complications such as massive hemorrhage and venous air embolism The challenges presented by this surgery include providing a relatively C H A P T E R : N EU R O VA S C U L A R S U R G E RY “bloodless” surgical field and managing complicated patients with multiple medical comorbidities Each stage of the perioperative period requires the anesthesiologist to make careful decisions to provide optimal management of these patients ANESTHESIA FOR N E U R O VA S C U L A R P R O C E D U R E S Table 14.1 FOR SAH GRADE Despite improvements in the treatment of intracranial aneurysms, the morbidity and mortality associated with aneurysmal rupture remain high The incidence of intracranial aneurysms (IAs) varies between countries but has been reported to be present on autopsy in 0.2% to 9.9% of the general population Subarachnoid hemorrhage (SAH) due to rupture of an aneurysm affects 30,000 Americans per year and is responsible for approximately 5% of all strokes [13, 14] Furthermore, an estimated 6700 in-hospital deaths occur each year as a result of aneurysmal SAH in the United States, and this is associated with a 30-day mortality rate of 45% [14] A large proportion of patients with a ruptured aneurysm suffer from additional morbidity in the form of rebleeding or vasospasm Although the clinical prognosis remains disappointing after a ruptured aneurysm, careful anesthetic management during surgical clipping or endovascular coiling is paramount to good outcomes CRITERIA Unruptured aneurysm Asymptomatic or minimal headache and nuchal rigidity Moderate to severe headache, nuchal rigidity; no neurologic deficit other than cranial nerve palsy Drowsiness, confusion, or mild focal deficit Stupor, hemiparesis, possible early decerebrate rigidity, vegetative disturbance Coma, decerebrate rigidity, moribund I N T R AC R A N I A L A N EU RY S M S Introduction THE HUNT AND HESS CLINICAL GRADES Table 14.2 THE GLASGOW COMA SCALE FEATURE SCORE Eye opening Spontaneous To speech To pain None Verbal response Oriented Confused conversation Inappropriate words Incomprehensible sounds None Best motor response Obeys commands Preoperative Management Treatment of intracranial aneurysms in the twenty-first century consists of either surgical clipping or endovascular coiling The anesthetic considerations for patients undergoing clipping or coiling are often the same and are partially based on the preoperative condition of the patient Assessing the severity of the patient’s SAH (if any) is an important part of the preoperative evaluation of these patients Although many methods of objectively grading the clinical findings associated with aneurysmal bleeding have been proposed, the most commonly used scoring systems are the modified Hunt and Hess grading scale and the Glasgow Coma Scale ( Tables 14.1 and 14.2) The Hunt and Hess score correlates not only with surgical risk and prognosis but also with the degree of associated cerebral pathophysiology and likelihood of vasospasm [15] Patients with lower Hunt and Hess scores are likely to have relatively normal ICP and intact CBF autoregulation, while those with a higher score will probably have more aberrant pathophysiology, including intracranial HTN, impaired autoregulation, and cerebral edema Other classifications, such as the Fisher grading scale, are used to predict the risk and severity of cerebral vasospasm after SAH [16] ( Table 14.3) Localizes to pain Flexion or withdrawal Abnormal flexion (decorticate) Abnormal extension (decerebrate) No response (flaccid) It is also important to assess the patient’s neurologic status with particular attention to the presence of preoperative focal deficits Patients with lower Hunt and Hess clinical grades are less likely to present with cerebral pathophysiology (e.g., intracranial HTN, impairment of cerebral autoregulation) than are patients with higher-grade pathology Table 14.3 FISHER GRADES IN SAH GRADE JESS BRALLIER CT FINDING(S) No blood detected Diffuse thin layer of subarachnoid blood (vertical layers