Anesthesia for awake craniotomy

INTRODUCTION — Awake craniotomy (AC) is most commonly used to allow mapping for resection of brain tumors near eloquent regions of the cerebral cortex, and occasionally for epilepsy surgery. In some institutions, supratentorial craniotomies without such indications are increasingly performed with patients awake, in order to reduce length of stay, and intensive care unit admissions, and to avoid the risks of general anesthesia.

The patient is not necessarily awake throughout the entire craniotomy but is conscious and cooperative during the portions of the procedure that involve testing. The success of AC depends on careful patient selection, and coordination between experienced anesthesia and surgical teams.

This topic will discuss anesthetic management for AC (table 1). General concerns for anesthesia for craniotomy, and anesthesia for placement of deep brain stimulators, are discussed separately. (See "Anesthesia for craniotomy in adults" and "Anesthesia for deep brain stimulator implantation".)

INDICATIONS — The most common surgical indication for AC is to allow functional cortical mapping for brain tumors, and occasionally vascular lesions or epileptogenic foci, close to eloquent cortex. Eloquent cortex refers to those parts of the brain that control motor, sensory, or language function. AC may also be used to facilitate electrocorticography for seizure focus localization, to minimize interference from anesthetic medications. AC may be performed without these indications, in order to facilitate enhanced recovery and reduce resource utilization. In some centers, selected patients are discharged on the day of surgery after AC [1,2]. (See 'Postoperative care' below.)

●Functional cortical mapping of eloquent brain function – The primary goal of AC for a brain lesion near eloquent cerebral cortex is to enable a tailored resection, to theoretically maximize the extent of the tumor resection and minimize the risk for neurological injury [3,4]. AC is often appropriate for mapping language and sensorimotor function [5]; in addition to the baseline individual variability in the cortical regions associated with these functions, cerebral topography may be distorted by tumor infiltration, radiotherapy, or previous surgery [6,7].

The literature on the outcomes of AC for tumor consists mostly of prospective cohort studies and retrospective chart reviews [8,9], with the exception of one small randomized trial [10]. Most [8,11,12], though not all [9,10,13], studies have reported a lower incidence of new and permanent postoperative neurologic deficits and higher gross total tumor resection with AC, compared with resection under general anesthesia. Some studies have found improved overall survival with awake resection.

•Postoperative neurologic deficit – A 2020 meta-analysis of 17 observational studies of glioma resection found similar incidences of early and late neurologic deficits with awake craniotomy compared with resection under general anesthesia [13]. There was a trend towards a higher mean extent of resection. In contrast, a propensity score-matched analysis of 536 patients in an international cohort study who underwent awake or asleep craniotomy for resection of glioblastoma in eloquent cortex, awake craniotomy was associated with increased likelihood of gross total resection and lower rates of neurologic deficits at both three months (22 versus 33 percent) and six months (26 versus 41 percent) postoperatively [12].

•Survival – A multicenter retrospective cohort study including approximately 900 patients who underwent resection of high-grade glioma found similar progression-free survival and overall survival with awake craniotomy versus general anesthesia [9]. However, in the cohort study of patients with high grade glioma described above, awake craniotomy was associated with longer overall survival (median 17 versus 14 months) and progression-free survival (median 9 versus 7.3 months) [12].

●Electrophysiological mapping and recording – Electrocorticography is an invasive electrophysiological technique for direct recording of cortical potentials from the surface of the brain, to localize seizure foci (picture 1). Cortical or subcortical signals are easily abolished by anesthetic agents. Thus AC may be performed to minimize the pharmacologic interference with the recordings that would occur under general anesthesia [14,15].

The need for AC for resection of epileptogenic foci has decreased with advancements in presurgical imaging techniques [16]. In some cases, AC for these procedures may preserve language function and predict seizure free outcomes. Intraoperative electrocorticography can help guide the required extent and completeness of the resection [15,16].

●Improving perioperative outcomes – Craniotomy may be performed awake to reduce the need for intensive care and the length of hospital stay, and in some cases, to reduce complications associated with general anesthesia. Examples of procedures that are commonly performed awake, without the need for functional mapping or electrocorticography, include stereotactic brain biopsy, ventriculostomy, and resection of small brain lesions [3,17]. In some centers, AC is used routinely for resection of supratentorial tumors [18].

A number of studies have reported shorter length of stay and reduced or eliminated intensive care unit (ICU) stay for AC, compared with general anesthesia [8,18], though postoperative disposition varies among institutions. (See 'Postoperative care' below.)

In one prospective observational single institution study involving 200 patients who had AC for tumor resection, the median length of hospital stay was three days, and the median time spent in the ICU was zero days [17]. This study spanned seven years; for the last 50 patients, 10 percent spent time in the ICU, and the median length of hospital stay was one day. (See 'Postoperative care' below.)

STEPS OF SURGERY — The surgical techniques that may be unique to awake craniotomy are cortical mapping and electrocorticography.

Cortical mapping — For craniotomy that involves brain mapping, the surgeon stimulates cortical areas of interest with the patient awake, using a bipolar or monopolar stimulator probe, and assesses the patient response to stimulation [19].

●During motor mapping, the patient is observed for abnormal involuntary movements or movement disturbances in the contralateral face, arm, and/or leg.

●During sensory mapping, the patient is asked to report abnormal sensations, such as paresthesia.

●Language mapping involves tests such as naming objects, counting numbers, reading single words, and/or repeating complex sentences. The patient is monitored for language deficits such as speech arrest, expressive or receptive aphasia during cortical stimulation.

●Visual mapping involves monitoring for abnormal visual phenomena (eg, visual hallucinations or phosphenes), or visual field cuts.

The extent to which the anesthesiologist is involved in sensory and motor mapping depends on institutional practice and the extent of resection. For complex mapping of language and visual areas of the brain, neuropsychologists or speech language therapists are often involved.

Electrocorticographic recordings — In patients undergoing epilepsy surgery, electrocorticographic (ECoG) recordings are performed for intraoperative localization of the epileptogenic focus. Electrodes are placed on the surface of the brain over and adjacent to the suspected epileptogenic foci [14,15]. The quality of ECoG recording is affected by the medications that may be administered for anesthesia or sedation. In particular, propofol infusion should be discontinued at least 20 minutes prior to ECoG recording. If necessary, the epileptogenic focus may be stimulated by administration of small doses of methohexital (10 to 50 mg), thiopental (25 to 50 mg), propofol (10 to 20 mg), or etomidate (2 to 4 mg) [14]. The author administers etomidate 2 mg IV in this setting.

PREOPERATIVE EVALUATION — All patients should have a preoperative history and focused physical examination before anesthesia. Preoperative evaluation for craniotomy in general is discussed separately. (See "Anesthesia for craniotomy in adults", section on 'Preoperative evaluation'.)

Preoperative airway evaluation is particularly important in anticipation of AC, as access to the airway and options for airway management are limited during these procedures. A plan for elective or emergent airway management should be determined preoperatively. In addition, patients who are at risk for airway obstruction with sedation (eg, severe obesity, patients with obstructive sleep apnea) should be identified.

Careful patient selection and preparation are critical to the success of an awake procedure, and should be coordinated between the surgeon and anesthesiologist. Patients who are identified as candidates for AC by the surgeon should be evaluated in advance of surgery, preferably in a preoperative anesthesia clinic.

Well-motivated and mature patients who are able to tolerate lying still for several hours, and can cooperate during testing, are the best candidates for AC. In some centers, formal preoperative psychologic or psychiatric evaluation is performed to help guide patient selection [20,21].

Criteria for patient selection vary among surgeons and institutions. At the author's institution, the only absolute contraindications for AC are patient refusal and severe claustrophobia. Relative contraindications include conditions that increase the risk of sedation failure, prevent cooperation with necessary testing, or increase the risk of airway compromise, including the following:

●Anxiety disorders, emotional instability, claustrophobia

●Significant dysphasia

●Confusion or somnolence

●Alcohol or drug abuse

●Chronic pain disorders

●Low pain tolerance

●Severe obesity

●Obstructive sleep apnea

●Anticipated difficult airway

●Uncontrolled coughing

●Dyspnea when lying flat

AC is usually avoided when high blood loss (>750 to 1000 mL) is anticipated, such as in patients with highly vascular tumors and tumors close to cerebral venous sinuses.

Preoperative laboratory evaluation and medication management prior to craniotomy are discussed separately. (See "Anesthesia for craniotomy in adults", section on 'Preoperative evaluation'.)

We ask patients who are taking antiepileptic drugs (AEDs) preoperatively to continue these medications up to and including the day of surgery. AEDs will not interfere with electrocorticography, and withholding AEDs increases the risk of intraoperative clinical seizures. However, in contrast with craniotomy performed under general anesthesia, we do not routinely administer intraoperative seizure prophylaxis during AC in patients who do not take AEDs chronically, since AEDs are sedating and can interfere with testing for cortical mapping.

PREOPERATIVE PATIENT PREPARATION — In addition to medical optimization in anticipation for craniotomy, patients who undergo AC should be prepared psychologically. The anesthesia clinician should develop rapport with the patient, and should discuss the rationale for awake surgery, the sequence of the procedure, expected degree of pain and discomfort, tasks required for testing, and the possibility of adverse events.

ANESTHETIC MANAGEMENT — There is wide variation in the anesthetic management for AC. Numerous case series and reports of individual institutional practice have been published. General considerations and our strategy for management of AC are discussed here (table 1).

Premedication — Premedication for craniotomy should be individualized based on the patient's level of anxiety, baseline neurologic status, comorbidities, and the plan for anesthesia. We do not routinely administer premedication preoperatively, though we administer midazolam if necessary in the operating room at the start of anesthesia. Benzodiazepines should be avoided for patients who undergo electrocorticography, since they suppress seizure foci and interfere with recording. (See "Anesthesia for craniotomy in adults", section on 'Premedication'.)

Monitoring — Standard American Society of Anesthesiologists (ASA) monitors (ie, electrocardiogram [ECG], blood pressure [BP], pulse oximetry, oxygen analyzer, continuous end-tidal carbon dioxide [ETCO₂] analyzer) may be sufficient for many ACs. The decision to place an intraarterial catheter, or to monitor for venous air embolism, should be based on patient factors and the surgical procedure. Arterial catheters are rarely placed at the author's institution, where the standard anesthetic technique is conscious sedation for AC. Intraarterial catheters are more commonly placed at other centers, particularly those that use an asleep-awake-asleep technique [22]. (See "Anesthesia for craniotomy in adults", section on 'Monitoring'.)

A processed EEG monitor (eg, bispectral index [BIS], Entropy or SedLine) may facilitate regulation of the dose of anesthetic agents, to allow rapid awakening for intraoperative language testing [23]. Placement of the sensors for these monitors on the forehead may not be possible during some craniotomies (eg, frontal craniotomy).

We do not routinely place a Foley catheter for AC. We do place a Foley catheter when surgery is likely to be longer than four hours, and when mannitol will be administered intraoperatively.

Positioning — The patient may be placed in the supine, semi sitting, or lateral position, depending on surgical requirements. The patient's head may be held in skull pins with a Mayfield apparatus, or in some cases, positioned on a gel donut.

Extreme flexion and rotation of the head should be avoided, to minimize airway obstruction or difficulty with airway management with an open cranium.

Every effort should be made to make the patient as comfortable as possible, for what may be a several hour (or more) procedure. Discomfort from prolonged positioning is a common complaint among patients who undergo AC [24-27]. Measures to minimize position related discomfort include the following:

●The operating table and all contact points should be well padded.

●The patient should be kept at a comfortably warm temperature, using warm blankets or a forced air warming blanket.

●A direct line of sight should be created between the patient and the anesthesia clinician, with space created around the patient's face under the drapes.

●The operating room should be kept as quiet as possible, with a sign on the door alerting staff that the patient is awake.

We use a microphone during AC to facilitate patient communications with the staff [14]. The microphone is particularly useful during language mapping, as it allows the surgeon to hear the patient's responses.

Local anesthesia — The scalp must be anesthetized for skull pinning, for the incision during ACs performed with conscious sedation, and to avoid pain on emergence for procedures performed with an asleep-awake anesthetic technique. Pin sites are usually anesthetized with local infiltration of 1 to 2% lidocaine at the site. The scalp can be anesthetized with regional field block, using local anesthetic infiltration around the incision and at pin sites, or with a scalp block.

The nerve blocks required for a scalp block for AC depend on the location of the incision and craniotomy (figure 1); a full scalp block requires bilateral injection of six nerves (figure 2), and requires injection of approximately 40 mL of local anesthetic (LA) solution. A long acting LA (ie, 0.25% bupivacaine, 0.2% ropivacaine, or 0.25% levobupivacaine) should be administered, with epinephrine 1:200,000, to maximize block duration and minimize systemic absorption. The technique for scalp block is discussed separately. (See "Scalp block and cervical plexus block techniques", section on 'Scalp block'.)

Local anesthetic systemic toxicity is always a possibility when such large volumes of LA are used, both during initial infiltration, and if further injection is required later during the procedure. The total allowable dose of LA should be discussed with the surgeon, and it is helpful to have a protocol in place for LA administration over the course of the procedure. (See "Local anesthetic systemic toxicity", section on 'Local anesthetic dose'.)

One such protocol is as follows:

●Limit initial scalp infiltration to ≤2.5 mg/kg lean body weight for bupivacaine or ropivacaine

●If re-dosing is required:

•two to four hours after initial dose, administer less than or equal to one-fourth of initial dose

•four to eight hours after initial dose, administer less than or equal to one-half of initial dose

•>8 hours after initial dose, can re-administer full initial dose

(See "Overview of peripheral nerve blocks", section on 'Local anesthetic systemic toxicity'.)

Despite an adequate scalp block, patients may have pain during the procedure unless opioids are administered, and up to 30 percent of patients recall considerable pain during the procedure [27]. The scalp block may inadequately cover the incision, the patient may have pain from other structures, or the scalp block may wear off during prolonged surgery. In one study, scalp block was performed with a mixture of lidocaine and ropivacaine prior to incision for AC with an asleep-awake-asleep anesthetic technique [28]. Nineteen percent of patients complained of moderate pain when awoken for testing, and another 17 percent had pain by the time they were reanesthetized.

Manipulation of the dura is intensely painful, especially with dissection in close proximity to meningeal vessels. Thus the surgeon may have to infiltrate the dura with local anesthetic when conscious sedation is used for AC [4]. Local anesthetic infiltration into the temporalis muscle may also be required for pain during dissection for pterional craniotomy. In addition, local anesthetic infiltration of the scalp may be required for closure at the end of surgery.

Choice of anesthetic technique — Most strategies for anesthesia for AC include either conscious sedation throughout, or general anesthesia with intraoperative awakening for brain mapping. General anesthesia may be used for both the beginning and the end of the procedure (ie, asleep-awake-asleep), or only for the beginning (ie, asleep-awake). No particular technique is demonstrably better than any other, and the choice of technique is based on clinician and institutional preference. At the author's institution, conscious sedation is the standard AC technique. A meta-analysis of 47 studies that compared asleep-awake-asleep with conscious sedation for AC reported no differences in intraoperative seizures, new neurologic dysfunction, or failure of AC [29]. Importantly, the need for airway management is determined by the choice of anesthetic technique. (See 'Airway management' below.)

Conscious sedation — When conscious sedation is used without general anesthesia, sedation is administered during the initial stimulating portions of the procedure, then stopped or reduced during cortical mapping, and resumed for resection and closure. Moderate sedation (ie, conscious sedation) should be the goal (table 2); the patient should respond purposefully to verbal or tactile stimulation, the airway should be maintained without intervention, ventilation should be adequate, and hemodynamics stable without support. Excessive sedation should be avoided, as it increases the risk of airway obstruction, respiratory depression, and apnea. If necessary, a nasal trumpet (ie, nasopharyngeal airway) is usually well tolerated by patients who undergo moderate sedation [30].

Choice of medications for conscious sedation — The choice of anesthetic agents for AC depends on the requirement for functional cortical mapping and intraoperative electrocorticography [4,14,31]. Drugs commonly used for conscious sedation include propofol, midazolam, remifentanil, fentanyl, and dexmedetomidine [4,32-34]. Any combination of these drugs may be administered as continuous infusions, bolus injections, target controlled infusions, or patient controlled boluses [35]. Benzodiazepines should be avoided during ACs that involve electrocorticography.

Propofol (50 to 150 mcg/kg/min) and remifentanil (0.01 to 0.05 mcg/kg/min) infusions have become widely used, because their rapid onset and short duration of action allows titration of the depth of sedation as required by the surgery. Other opioids, including fentanyl, alfentanil, and sufentanil are often administered as well [34]. (See "Monitored anesthesia care in adults", section on 'Propofol' and "Monitored anesthesia care in adults", section on 'Opioids'.)

Dexmedetomidine is increasingly used for AC, with or without propofol, midazolam, and/or opioids [31,32,36-39]. (See "Monitored anesthesia care in adults", section on 'Dexmedetomidine'.)

The primary benefits of dexmedetomidine for AC are that it does not interfere with electrocorticography and may cause less respiratory depression than other sedatives and opioids. The dose of dexmedetomidine infusion must be titrated carefully, since prolonged administration can cause delayed reversal of sedation after the drug is discontinued [40]. A small study of patients who underwent conscious sedation for AC reported similar efficacy of sedation and quality of brain mapping in patients randomly assigned to receive propofol/remifentanil or dexmedetomidine, in addition to fentanyl [38]. Arousal time after discontinuation of the study drug was also similar (five to eight minutes). There were fewer respiratory adverse events in the dexmedetomidine group (ie, airway obstruction or apnea). However, some studies in other settings have reported upper respiratory obstruction and apneic episodes during dexmedetomidine sedation, particularly during bolus administration [41,42]. Two small volunteer studies that compared propofol with dexmedetomidine reported similar levels of upper respiratory obstruction and/or reduced respiratory drive [43,44]. Thus, dexmedetomidine should not be viewed as protective against respiratory depression, especially in high-risk patients.

Asleep awake asleep — An asleep-awake-asleep technique is increasingly used for AC. A wide variety of drugs regimens and a number of airway management strategies have been described. General anesthesia is induced, and the airway is often secured with endotracheal intubation or placement of a supraglottic airway. General anesthesia is maintained during positioning, skull pinning, craniotomy, and dural opening. Once dura is open, the patient is awakened, and the airway is removed to allow for patient participation during cortical mapping. Once mapping is completed, general anesthesia is induced again, an airway device is reinserted, and the patient remains anesthetized for the remainder of the procedure.

Choice of anesthetic agents for general anesthesia — Anesthetic drugs should be chosen to allow stable hemodynamics, and a rapid and smooth transition to the awake state, with minimal interference with electrical stimulation used for mapping. Total intravenous anesthesia is commonly used, including propofol for induction, followed by infusion of propofol, short acting opioids (eg, remifentanil infusion or fentanyl boluses), with or without dexmedetomidine infusion [22,45-48]. Inhalation anesthesia has also been used during the asleep portion of AC [49].

Airway management — A variety of airway management strategies have been described for the asleep portion of AC, including endotracheal intubation, use of a supraglottic airway, and administration of supplemental oxygen by facemask, nasal cannulae [50], or nasopharyngeal airway [22]. Supraglottic airways are commonly preferred, as they allow controlled ventilation, avoid airway obstruction, and may facilitate a smoother transition to the awake state, compared with endotracheal tubes.

Any form of airway manipulation between the asleep and awake states may cause laryngospasm or coughing [45,48], which can cause surgical bleeding, increased intracranial pressure, or injury related to skull pin fixation.

Reestablishing airway control for induction of anesthesia for closure may be challenging. Access to the airway in this setting is limited, the head is in a fixed position that is often not optimal for airway management, and direct laryngoscopy is usually not possible. Options include insertion of a supraglottic airway, endotracheal intubation using an intubating supraglottic airway, videolaryngoscope or flexible scope, or spontaneous ventilation with a facemask or nasopharyngeal airway. (See "Flexible scope intubation for anesthesia" and "Supraglottic devices (including laryngeal mask airways) for airway management for anesthesia in adults", section on 'Supraglottic airways as conduits for intubation'.)

Administration of supplemental oxygen using an unsecured airway during surgery on the head increases the risk of airway fire with electrocautery. The risk of airway fire and strategies to prevent it are discussed separately. (See "Fire safety in the operating room", section on 'Risk prevention: High-risk procedures' and "Fire safety in the operating room", section on 'Special precautions during airway surgery'.)

AUTHOR'S STRATEGY FOR AWAKE CRANIOTOMY — There are many reasonable strategies for anesthetic management of AC. Our preferred technique for AC is conscious sedation, as follows. We use an asleep-awake asleep technique for patients who may not tolerate the procedure under conscious sedation. (See 'Indications' above.)

For either conscious sedation or asleep-awake-asleep techniques, we apply standard monitors, and use invasive arterial blood pressure monitoring when indicated by patient comorbidities. We insert a Foley catheter for surgery expected to last >4 hours, and/or if administration of mannitol is planned.

Strategy for conscious sedation — We administer sedation with a combination of dexmedetomidine with propofol, as follows:

●Administer midazolam 1 to 2 mg intravenous (IV), and fentanyl 25 to 50 mcg IV (no midazolam if electrocorticography is planned).

●Administer loading dose of dexmedetomidine 1 mcg/kg IV, dose adjusted for patient factors, followed by infusion dexmedetomidine 0.3 to 0.7 mcg/kg/hour, titrated to level of sedation. Add propofol infusion as necessary (start at 25 mcg/kg/min, titrate to level of sedation (25 to 75 mcg/kg/min).

●For skull pinning, administer propofol boluses until patient is unarousable with tactile stimulation (propofol 10 mg IV boluses, total usually 30 to 40 mg IV). Surgeon infiltrates pin sites with 1 or 2% lidocaine, then places skull pins. Administer fentanyl 25 to 50 mcg IV if necessary to tolerate pinning.

●When patient awakens, check that head, neck, and shoulders are comfortable, and readjust position if necessary and as possible.

●The surgeon infiltrates the scalp with up to 40 mL of 0.25% bupivacaine with epinephrine 1:200,000.

●Additional boluses of fentanyl 25 to 50 mcg IV, with or without propofol 10 to 20 mg IV may be administered, or infusions increased, for pain as needed during skull pinning, scalp infiltration, or during painful portions of surgery (eg, temporalis muscle dissection, dural opening or closure).

●Stop propofol infusion after bone flap is removed, and wait for the patient to wake up for cortical mapping. Stop or reduce dexmedetomidine infusion at the same time, depending on the depth of sedation. For some patients, dexmedetomidine can be continued during mapping.

●Restart sedation after mapping, with propofol bolus 10 to 20 mg IV, followed by infusion as before mapping.

●During scalp closure, administer ondansetron 4 mg IV, discontinue propofol and dexmedetomidine infusions, and administer fentanyl 25 mcg IV, repeated as necessary for pain.

Strategy for asleep-awake-asleep technique — For patients who require an asleep-awake-asleep technique, we prefer to use total intravenous anesthesia (TIVA) with propofol and remifentanil, and to manage the airway with a laryngeal mask airway, as follows:

●Asleep portion – After pre-oxygenation, induce general anesthesia with propofol (2 to 2.5 mg/kg IV) and fentanyl (0.5 to 1 mcg/kg IV). Test and note the degree of difficulty with mask ventilation before inserting a laryngeal mask airway (LMA).

•Maintain anesthesia with TIVA using propofol (100 to 150 mcg/kg/min) and remifentanil (0.05 to 0.1 mcg/kg/min). Maintain spontaneous ventilation if possible; controlled ventilation may be required to reduce PaCO₂ for brain relaxation.

•After skull pinning, position the patient carefully, avoiding extreme neck rotation and/or flexion, and ensuring access to the face for airway manipulation. If there are concerns about the airway after the head fixation, before finalizing positioning, remove the LMA, verify the ability to ventilate by mask with an oral airway in place, and that the LMA can be reinserted easily. If necessary, adjust the head position.

●Awake portion – Call for assistance for awakening.

•Assure spontaneous ventilation, then turn off propofol, reduce remifentanil to 0.03 to 0.05 mcg/kg/min, and administer 100 percent oxygen. Warn the surgeon that the patient might cough, and gently suction the oropharynx. Extubate or remove the supraglottic airway when awake.

•If necessary, continue remifentanil infusion (0.03 to 0.05 mcg/kg/min) for analgesia during awake procedure.

●Asleep portion – Induce general anesthesia with propofol and fentanyl as before, and reinsert the LMA. Maintain anesthesia with TIVA, as before, for the rest of the procedure.

COMPLICATIONS — Intraoperative complications of AC include seizures, respiratory complications, pain, nausea and vomiting, hemodynamic perturbations, brain edema, and failure of the awake procedure (ie, either conversion to general anesthesia, or failure to complete mapping). Other complications include those that may occur during any craniotomy, such as venous air embolism. Complications of AC and their causes and treatment are shown in a table (table 3).

●Seizures – Seizures may occur at any time during AC, though they occur most commonly during stimulation for brain mapping. The reported incidence of seizures during AC is from 2 to 20 percent [2,11,17,18,29,45,51-54] and they are more common with tumors in frontal lobe and in patients with a history of seizures [51]. Many intraoperative seizures are focal, brief, and resolve spontaneously, whereas others are generalized. If the dura is open when a seizure occurs, the first line treatment should be irrigation of the brain with sterile iced saline. If necessary, propofol bolus (10 to 20 mg IV), or midazolam (1 to 2 mg IV) should be administered to terminate the seizure. Propofol is preferred in this setting, rather than midazolam, if electrocorticography is going to be performed. (See 'Electrocorticographic recordings' above.)

Generalized seizures should be treated immediately to avoid patient injury and airway compromise. Airway support may be required, including induction of general anesthesia and airway control, for refractory seizures or after repeated treatment.

●Respiratory complications – Airway obstruction, hypoventilation and hypercarbia, and oxygen desaturation may occur during AC [22,50,55]. In most cases, minor airway management techniques (eg, jaw thrust, placement of a nasopharyngeal airway, or mask ventilation) resolve such events, but occasionally endotracheal intubation or placement of a supraglottic airway is required.

●Brain swelling – Airway obstruction or hypoventilation with hypercarbia can cause brain swelling. Sedation should be decreased, and the patient should be instructed to breathe deeply. Assisted ventilation by mask, or airway control with endotracheal intubation or placement of a supraglottic airway with hyperventilation may be required. Elevation of the patient's head and intravenous mannitol are other possible treatments. (See "Anesthesia for craniotomy in adults", section on 'Intraoperative cerebral edema'.)

Patients who develop brain swelling may become uncooperative and require general anesthesia.

●Nausea and vomiting – Nausea occurs in approximately 4 percent of patients who undergo AC with conscious sedation [22,56], and may be related to administration of opioids, anxiety, or surgical stimulation. Vomiting rarely occurs if nausea is treated with an antiemetic.

The dexamethasone that most patients receive preoperatively before craniotomy, and the propofol that is commonly administered for anesthesia or sedation, are synergistic antiemetics. We administer ondansetron intraoperatively if the patient complains of nausea, and routinely administer ondansetron 4 mg IV at the end of surgery to prevent postoperative nausea and vomiting. An advantage of ondansetron during AC, compared with some other antiemetics, is that it does not cause sedation. (See "Postoperative nausea and vomiting", section on 'Antiemetics'.)

●Hemodynamic perturbations – Hypertension and tachycardia occur commonly during AC [22,55], and should be treated with increased sedation or pain control as appropriate, and with vasodilators and beta blockers as necessary.

●Failed AC – Failure of AC (ie, unplanned conversion to general anesthesia, or failure to complete brain mapping) may occur for a variety of reasons, including failure of communication with the patient, uncontrolled intraoperative seizures, airway events, or brain swelling [57,58]. Failed ACs are associated with a lower incidence of gross-total resections, increased postoperative speech deterioration, and a longer length of stay [21].

Failed AC is reported in zero to approximately 6 percent of awake craniotomies [8,10,18,21], and may be minimized by appropriate patient selection. Among various preoperative factors, low Karnofsky Performance Status (KPS) score (<70) has been associated with emotional intolerance during awake craniotomy [59]. (table 4)

POSTOPERATIVE CARE — Immediate postoperative care is similar after AC and those performed under general anesthesia, with respect to hemodynamic management, provision of analgesia, neurologic monitoring, and management of complications. In general, postoperative analgesic requirement and the incidence of postoperative nausea and vomiting are lower than craniotomy under general anesthesia [60,61].

Postoperative disposition varies among institutions. Intensive care admission, which is routine after craniotomy under general anesthesia, has decreased in many centers, and may be restricted to patients with significant medical comorbidities or surgical complications. Most patients in such centers, including the author's, are admitted to the post-anesthesia care unit (PACU) from the operating room, and are sent to an inpatient ward after a minimum two hour PACU stay.

In some centers, patients may be discharged the day of surgery after AC, with a modified protocol for immediate postoperative care. As an example, in one institution, carefully selected patients were discharged to home approximately six hours postoperatively, following a two hour PACU stay, a computerized tomography scan at four hours after surgery to rule out hemorrhage and brain edema, and two more hours of monitoring [62].

PATIENT PERCEPTION AND SATISFACTION — Carefully selected, well-informed patients are likely to tolerate an AC well and patient satisfaction after AC is high [1,24,26,27,58,63,64].

Most patients recall minor discomfort or pain, often related to the stereotactic frame, body positioning, or pain during manipulation of the dura. In one prospective study involving 50 patients who were randomly assigned to conscious sedation with propofol and either remifentanil or fentanyl, 93 percent of patients in both groups were completely satisfied with the experience when asked at 1 hour, 4 hours, and 24 hours postoperatively [1].

SUMMARY AND RECOMMENDATIONS

●Indications – Awake craniotomy (AC) is most commonly used to allow mapping for resection of brain tumors near eloquent regions of the cerebral cortex, and occasionally for epilepsy surgery. AC may also be performed in order to facilitate enhanced recovery and reduce resource utilization. (See 'Indications' above.)

●Preanesthesia evaluation – Careful patient selection and preparation are critical to the success of AC. Well-motivated and mature patients who are able to tolerate lying still for several hours, and can cooperate during testing, are the best candidates for AC. (See 'Preoperative evaluation' above.)

Preoperative airway evaluation is particularly important in anticipation of AC, as access to the airway and options for airway management are limited. A plan for elective or emergent airway management should be determined preoperatively. (See 'Preoperative evaluation' above.)

●Local anesthesia – The scalp must be anesthetized with local anesthetic infiltration or scalp block (figure 1 and figure 2) for skull pinning, for the incision during ACs performed with conscious sedation, and to avoid pain on emergence for procedures performed with an asleep-awake anesthetic technique. (See 'Local anesthesia' above.)

●Awake versus asleep-awake-asleep – Most of the varied strategies for AC involve either conscious sedation throughout the procedure, or general anesthesia for the beginning and end, with the patient awake during mapping (asleep-awake-asleep) (table 1). (See 'Choice of anesthetic technique' above.)

No particular technique is demonstrably better than another. Importantly, the need for airway management is determined by the choice of technique.

●Conscious sedation – For conscious sedation, commonly used medications include propofol, midazolam, dexmedetomidine, fentanyl, and remifentanil, administered by bolus, infusion, and/or target controlled infusion (table 1). Midazolam should be avoided for patients who undergo electrocorticography, and propofol should be turned off at least 20 minutes prior to electrocorticography. (See 'Choice of medications for conscious sedation' above.)

We prefer to use conscious sedation for most patients who undergo AC. Our strategy includes infusions of propofol and dexmedetomidine, with intermittent boluses of fentanyl. (See 'Strategy for conscious sedation' above.)

●Asleep-awake-asleep – For this technique, general anesthesia is induced, the airway is secured, and anesthesia is maintained until the dura is opened (table 1). The patient is then awakened, the airway device is removed, and cortical mapping is performed. General anesthesia is then induced again and maintained for the remainder of the procedure. (See 'Asleep awake asleep' above and 'Airway management' above.)

Total intravenous anesthesia is commonly used for this technique, including propofol for induction followed by infusion of propofol, short acting opioids (eg, fentanyl boluses or remifentanil infusion), with or without dexmedetomidine infusion. (See 'Choice of anesthetic agents for general anesthesia' above.)

When we use an asleep-awake-asleep technique, we use total intravenous anesthesia with a laryngeal mask airway. (See 'Strategy for asleep-awake-asleep technique' above.)

●Complications – Intraoperative complications of AC include seizures, respiratory complications, pain, nausea and vomiting, hemodynamic perturbations, brain edema, and failure of the awake procedure (ie, either conversion to general anesthesia, or failure to complete mapping) (table 3). (See 'Complications' above.)

Seizures occur most commonly during stimulation for brain mapping. First line treatment for seizures should be irrigation of the brain with iced saline. If necessary, propofol (10 to 20 mg IV) or midazolam (1 to 2 mg IV) should be administered.

●Postoperative care – Immediate postoperative care is the same for AC as it is for craniotomy with general anesthesia. Disposition after AC varies among institutions; intensive care admission after AC is avoided for many patients, particularly when conscious sedation is used. (See 'Postoperative care' above.)