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Vol. 73 - No. 10 MINERVA ANESTESIOLOGICA507MINERVA ANESTESIOL 2007;73:507-12 REVIEW ARTICLEAnesthetic management for neurosurgeryin awake patientsP. HANS, V. BONHOMMEDepartment of Anesthesia and Intensive Care Medicine, CHR de la Citadelle, Liege University Hospital, Liege, BelgiumABSTRACTNeurosurgery without general anesthesia is based on the necessity to avoid any interference between brain electro-physiological recordings and anesthetic agents, and the opportunity to have a patient able to follow commands and tocooperate during surgery. It includes not only several minimally invasive procedures, but also craniotomies for epilep-sy surgery or the removal of tumors located close to brain eloquent areas. Before surgery, the patient must be careful-ly evaluated, correctly informed and appropriately prepared. In the operating room, monitoring is important for con-ducting the anesthetic management, ensuring patientÕs comfort and safety, and meeting surgical requests. Propofoland remifentanil are frequently used for anesthesia, but sufentanil, local anesthetics and a2-agonists are also of primaryinterest. PatientÕs ventilation may be spontaneous, assisted or controlled. Airway management is a key point stronglyrelated to the anesthesia technique and the type of surgery. Airway may be secured with different airway devices andthe laryngeal mask appears to progressively replace the endotracheal tube. Respiratory, hemodynamic, and neurolog-ic complications as well as nausea and vomiting and loss of patientÕs cooperation may have disastrous consequences andshould be prevented rather than cared.Key words:Anaesthesia, methods - Neurosurgery - Surgery. Nowadays, a quite important part of neuro-surgery does not necessarily require com-pletely anesthetized patients, but does certainlyrequire skilled and experienced anesthesiologists.This type of surgery is not limited to awake cran-iotomies only and can be discussed in the field ofa more general context.Basically, neurosurgery without general anes-thesia is not a new story. In the second half of the19thcentury, awake craniotomies for epilepsy sur-gery were already performed in patients underlocal anaesthesia.1Today, the concept of neuro-surgery in awake or waking up patients has consid-erably evolved and extended, in strong relation-ship with the outstanding progresses made in neu-rosurgical technology, monitoring of anesthesia,and also anesthetic agents and the way they aredelivered to the patients. Consequently, anesthe-siologists are more and more frequently involvedin this setting. This review paper aims at discussingthe role of the anesthetic management of patientsundergoing neurosurgical procedures without gen-eral anesthesia.Indications and objectivesIndicationsWe may consider three main reasons for per-forming neurosurgery without general anesthesia.The first reason is that no real benefit is expectedfrom general anesthesia. This situation may con-MINERVA MEDICA COPYRIGHT¨ ANESTHETICMANAGEMENTFORNEUROSURGERYINAWAKEPATIENTSMINERVA ANESTESIOLOGICAOctober 2007cern simple ventriculostomies, cerebral biopsiesunder stereotactic conditions and even some endo-scopic procedures performed in cooperativepatients. Indeed, a simplified endoscopic thirdventriculostomy under local anesthesia has beenreported in the literature.The second reason forperforming neurosurgery in awake patients is thenecessity to avoid any type of interference betweenthe evoked electrical activity of the brain, as it maybe required during electrodes placement for deepbrain stimulations or the realization of electro-cortical mapping in epilepsy surgery. The last rea-son of those awake neurosurgical procedures, whichis certainly the most important one, is the oppor-tunity to take advantage of the awake state of theate during surgery. That will be the case when thedeep brain stimulations, such as in Parkinson sur-gery, and also for the removal of tumors or evenvascular lesions located close to functional elo-quent areas of the brain such as motor, vision orlanguage areas. In this particular situation, theneurosurgeon has to cope with a difficult dilem-Indeed, a large resection will decrease the riskof recurrence of the lesion and increase the chanceof patientÕs survival but, in the meantime, it mayfavor the occurrence of a neurological deficit thatlife. Therefore, the challenge of tumor surgery per-formed in awake patients is to remove the maxi-mum amount of lesion without impairing neuro-Objectives Minimally invasive surgery is usually performedand analgesia. In contrast, craniotomies will morefrequently, although not systematically require oneor two phases of general anesthesia that are partof the so-called Òasleep awake asleep techniqueÓ, asdescribed by Huncke et al. for intraoperative lan-Whatever the strategy of anesthesia, the objec-tives of patientsÕ management are twofold: allowthe neurosurgeon to take advantage of the patientÕscooperation, and preserve general homeostasis.Achievement of the first objective will require opti-mal analgesia during nociceptive stimulations,sedation and anxiolysis with regard to specific sur-gical events, immobility and comfort throughoutthe procedure, and finally prevention of occur-rence of side effects or unpleasant events, such asnausea, vomiting or seizures. The second objec-tive aims at maintaining airway permeability, ade-quate ventilation, hemodynamic stability and brainrelaxation. It will also imply to avoid any interfer-ence between anesthetic agents and the electro-physiological activity of the brain. Hence, the anes-neurosurgical procedures can be rationally dis-cussed in two stages: what has to be done beforesurgery and how to proceed in the operating room? What has to be done before surgery? The preoperative phase includes the assessmentof the patient, the preparation of the patient andthe premedication.PatientÕs assessmentIn addition to the classical issues commonlyaddressed before any type of general anesthesia,the anesthesiologist should pay a particular atten-tion to specific points. He must anticipate a diffi-could favor upper airway obstruction or respirato-ry depression, such as obesity or a sleep obstructiveapnea syndrome. In epileptic patients, he shouldbe aware of the type and frequency of seizures aswell as the routine anticonvulsant therapy of thepatient. He should know the propensity of thepatient to present nausea and vomiting. In braintumor patients, he should evaluate the degree ofintracranial hypertension according to clinicalsigns and imaging. He should also evaluate thehemorrhagic risk of the procedure, depending onthe type of lesion, history of the patient and rou-tine medications. Finally, he should evaluate thedegree of anxiolysis, the tolerance to pain and anyneurological deficit that could impede the patientÕscooperation during surgery.Preparation of the patientObtaining the patientÕs confidence and agree-ment for cooperating during surgery is a key fac- MINERVA MEDICA COPYRIGHT Vol. 73 - No. 10 MINERVA ANESTESIOLOGICAANESTHETICMANAGEMENTFORNEUROSURGERYINAWAKEPATIENTStor of success. The psychological preparation mustbe considered as a team work that should involvethesiologist and nurse. The patient must beinformed regarding the sequence of events dur-ing surgery, the specific times where his coopera-tion will be required, and also the potential sideIt can also be useful to repeat a function-al test the day before surgery.PremedicationRegarding premedication, there is no generalrule but a case by case discussion that should referto different points. A conversation may be betterthan any medication, although drugs such as ben-zodiazepines, clonidine and atropine, are com-monly administered. Routine anticonvulsive med-ing tumor surgery and maintained in the thera-peutic range. Steroids must be considered to reducebrain edema in tumor surgery and also to preventnausea and vomiting in combination with specif-ic anti-emetic drugs, such as metoclopramide orondansetron.Finally in patients undergoing sur-gery for Parkinson disease or epilepsy, no specifictherapy will be given the day of surgery in anattempt to avoid any interference with electro-physiological recordings and evaluation of thepatientÕs response to deep brain stimulations. How to proceed in the operating room? In the operating room, the general philosophyis to make the patient as comfortable as possible,in a safe environment and throughout the entireperiod of surgery. This intraoperative manage-ment includes a preparation phase, the choice ofa strategy of anesthesia, the airway care, and final-ly the diagnosis and treatment of potential com-PreparationIn the operating room, drugs and equipmentshould be ready in advance. One or two intra-venous lines are placed. Patients are regularlyequipped with an ECG monitor, a blood pressuremeasurement device, a pulse oxymeter and, ideal-ly, a depth of anesthesia monitor. According tothe type of surgery, blood pressure can also bemeasured invasively, at the discretion of the anes-thesiologist. A urinary catheter and a temperatureprobe are usual. Pillows, mattress and warmingblanket may improve the patientÕs comfort andare useful to prevent pressure lesions.AnesthesiaAnesthesia for awake neurosurgery sounds firstas a paradoxical issue, but is nevertheless com-pletely justified. It most frequently relies on theconcept of monitored anesthesia care (MAC).should fulfill the following criteria: a sufficientdepth of anesthesia during opening and closure, afunctional testing, a smooth transition betweenanesthesia and consciousness and, finally, adequateventilation, immobility and comfort of the patientthroughout the entire procedure.available options that are susceptible to meet thosecriteria are either sedation or analgesia, or the so-Looking at the literature since 1988 to 2006,drugs and anesthetic agents that have been usedto provide sedation, analgesia or anesthesia to thosepatients include local anesthetics, different drugssuch as droperidol, midazolam, propofol andvolatile anesthetics and nitrous oxide, and ketamine. Today, the main agents actuallyemployed are bupivacaine and ropivacaine, sufen-tanil, remifentanil, and propofol. Regarding dexmedetomidine appears of increasing interestalthough it is not yet available in most Europeancountries. Drugs such as esmolol, labetalol andhydrazaline may also be part of the pharmacolog-Local anesthesia of the surgical field using ropi-vacaine or levobupivacaine with epinephrine 5µg/mL has been reported to be safe and effica-Regional blocks of upper and lowerextremity nerves have also been proposed to pre-vent involuntary movements in patients under-going awake craniotomy.Today, this techniqueappears to be abandoned or remains exceptional inthis particular setting. The three classical synthet- MINERVA MEDICA COPYRIGHT ANESTHETICMANAGEMENTFORNEUROSURGERYINAWAKEPATIENTSMINERVA ANESTESIOLOGICAOctober 2007ic opioids alfentanil, sufentanil and fentanyl havebeen used and combined with other drugs suchas droperidol, midazolam, propofol, etc.Morethan 10 years ago, they have been reported to havesimilar properties in patients undergoing epilep-sy surgery.Nowadays, sufentanil is still com-monly used, but remifentanil is gaining more andmore popularity.Remifentanil has well knownadvantages over the other synthetic opioids. Itsinteresting pharmacokinetic properties make it agood choice to provide excellent analgesia onrequest, and obtain a patient alert and able to coop-erate rapidly after stopping infusion. However, itmay favor respiratory depression.Propofol is thefirst choice hypnotic. It can be administrated usinga target control infusion technique, and its admin-istration can be guided by a depth of anesthesiamonitor and combined to remifentanil infusion.Dexmedetomidine is not available in all coun-tries but appears to be promising when used inprovides sedation close to natural sleep, has anxi-olytic and analgesic properties, decreases the use ofopioids and antihypertensive drugs without caus-ing clinically relevant respiratory depression can be administered when sophisticated neuro-logic testing is required.Finally, it is worth tonote that awake craniotomy is perfectly feasiblein pediatric patients. In particular, drugs such aspropofol and dexmedetomidine have been suc-Airway careAirway management is a major challenge dur-ing surgery in awake patients, and often stronglyrelated both to the type of surgery and the strate-Usually, spontaneous ventila-as well as during the awake phase of the asleepawake asleep technique. In contrast, ventilationwill be more frequently controlled or assisted dur-ing the phases of general anesthesia. Spontaneousventilation is quite common in minimally inva-sive procedures although it carries on some riskof upper airway obstruction and respiratory depres-sion. In spontaneously breathing patients, airwaylaryngeal mask airway (LMA), an oropharyngealor a nasopharyngeal device. All of them neithernecessarily secure the airway nor prevent pul-monary aspiration, but some may allow to applyventilatory support such as biphasic positive airwaypressure and proportional assist ventilation.In a recent report, a positive inspiratory and expi-ratory pressure has been successfully appliedthrough bilateral cannulation of the nares duringthe asleep phases of craniotomy and was shownto successfully improve ventilation parameters ina patient with an obstructive sleep apnea.Ventilation is more often controlled during theA couple of years ago, the old fashion to proceeding and closure of the skull, and extubated forfunctional testing or electrical mapping. It has alsobeen reported that lidocaine could be delivered tothe upper airway in order to avoid cough and gagreflexes.Endotracheal intubation is known toprevent aspiration and ensure adequate ventila-tion, but is not always easy to perform. It mayrequire a fiberoptic guide and is quite uncomfort-able for the patient. The less aggressive and morecomfortable alternative solution is to ÒsecureÓ theairway either with a laryngeal mask inserted undergeneral or even local anesthesia, or with a nasalmask which allows non invasive positive pressureventilation.The LMA has been proveneffective for airway management in pediatricFinally, it is also possible to controlthe patientÕs ventilation only during the openingphase of the surgical procedure, and to completesurgery after electrical mapping or functional test-breathing spontaneously without any tracheal orlaryngeal device.Potential complications of awake craniotomiesinclude upper airway obstruction and respirato-ry depression, tight brain, nausea and vomiting,seizures, decrease in the level of consciousness,neurological deficit and loss of patientÕs coopera-In this setting, prevention is betterthan care and the anesthesiologist may play a keyrole.The incidence of complications is quite vari-able and may be related to the strategy of anesthe- MINERVA MEDICA COPYRIGHT Vol. 73 - No. 10 MINERVA ANESTESIOLOGICAANESTHETICMANAGEMENTFORNEUROSURGERYINAWAKEPATIENTSsia. Recently, a general evaluation of monitoredanesthesia care for functional neurosurgery in 178patients emphasized a 16% overall complicationsIn a retrospective study on patients under-going awake craniotomy for tumor surgery, Sarangaccording to the anesthesia regimen.In the 99reviewed procedures, the incidence of respiratoryand hemodynamic complications was the lowestin patients who received total intravenous anes-thesia with propofol and remifentanil with a con-trolled ventilation using the LMA, compared tototal i.v. anesthesia and spontaneous breathingthrough a LMA, and to sedation and spontaneousbreathing through a nasal airway. In another ret-rospective study performed on 96 patients under-going functional neurosurgery and receiving propo-fol and remifentanil under spontaneous ventila-Finally, in more than 450patients undergoing epilepsy surgery under propo-fol and remifentanil, the asleep awake asleep tech-nique without a secured airway was associated toa higher rate of hypoxemia and hemodynamicTherefore, respiratory complications are notrare and may be life threatening. In a recent paperon injury and liability associated with monitoredanesthesia care, respiratory depression after absoluteor relative overdose of sedative or opioid drugscific mechanism in MAC claims, with a reportedthe editorial accompanying this paper, MACnot for minimal anesthesiology care.Respirationcomplications are prevented first by preoperativebut also by appropriate choice and titration of theanesthetic agent, monitoring respiratory rate andexpired CO, attention paid to the patientÕs posi-tion and continuous free access to the head. Expe-rienced anesthesiologists are required to manageThe incidence of nausea and vomit-ing is variable, depending on patientÕs history, typeIt canbe minimized by a judicious selection of anesthet-ic drugs combined to the administration of steroidsand specific anti-emetic medications. Seizures canthe perioperative period. They are best preventedby an appropriate therapy before surgery. Theirmanagement involves administration of anticon-quate ventilation, and may require a conversionto general anesthesia. Finally, the patientÕs refusalto cooperate may be due to different reasonsincluding bad preoperative preparation, inappro-priate and excessive sedation, insufficient analge-sia, uncomfortable position and a too long surgi-cal procedure. Some of them can be prevented,but the loss of patientÕs cooperation may alsorequire a conversion to general anesthesia for com-pleting surgery. 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Anesthesiology Paper has always been presented as a Refresher course, Annual Meeting of the ESA, Madrid, 3-6 June 2006.Address reprint requests to: Prof. P. Hans, University Department of Anesthesia and Intensive Care Medicine, CHR de la Citadelle, Boulevarddu 12e de Ligne 1, 4000 Liege, Belgium. E-mail: pol.hans@chu.ulg.ac.be MINERVA MEDICA COPYRIGHT