Anesthesia for Awake Craniotomy

Introduction

• AC facilitates resection of lesions in eloquent cortex by allowing direct patient feedback during neurological mapping. This method helps preserve neurological function and increase the extent of resection.
• Anesthetic management focuses on preserving patient comfort, ensuring airway patency, and facilitating patient cooperation with neurologic testing.
• In this summary, we discuss indications, patient selection, anesthetic techniques, complications, and outcomes based on contemporary reviews and recent comparative studies.

Rationale and Indications

• Real-time language or motor testing facilitates maximal safe resection while preserving neurologic function.^1-3 This functional advantage is supported by a large body of clinical data. For example, in the GLIOMAP study, AC, compared with GA for glioblastoma resection in eloquent areas, was associated with better neurologic outcomes and improved survival.⁴ This demonstrates that anesthetic strategies that facilitate reliable mapping can improve long-term functional and oncologic results.
• The primary indications for AC include:
  • tumors near the language, motor/sensory cortex,
  • epilepsy surgery requiring electrocorticography or functional mapping, and
  • lesions located near or involving critical white matter pathways.^1-3

Patient Selection and Preoperative Assessment

• Patient selection is a key determinant of procedural success.^1-3
• Essential criteria include:
  • Ability to cooperate with neurocognitive tasks
  • Adequate baseline language and cognition
  • Emotional stability
  • Reassuring airway and adequate cardiopulmonary reserve

Predictors of AC Failure

• A large observational series of ACs (n=609) identified several preoperative predictors for failure (e.g. intolerance of AC or conversion to deeper anesthesia/GA.)⁵
• Cognitive decline, dysphasia, and low Karnofsky Performance Status were significantly associated with emotional intolerance (n=13), which requires adjustments to sedation level or conversion to GA.
• Conversion to GA remained low (~2–3%), underscoring the need for careful counseling and risk stratification.

Patient Preparation

• Task rehearsal and clear expectation-setting reduce intraoperative anxiety and improve cooperation.^1-3
• Data from patient experience surveys show the importance of comprehensive preparation.⁶
  • Recollection of the procedure ranged widely (0–100%).
  • Most patients reported discomfort from head fixation and positioning.
  • Most remained satisfied and reported that AC provided a sense of control and therapeutic engagement.
  • Trust in the team and a clear preoperative explanation were important factors.

Perioperative Workflow and Multidisciplinary Coordination

• Successful AC requires a structured, coordinated multidisciplinary framework.^1-3 Teams typically include anesthesia, neurosurgery, neuropsychology, neurophysiological monitoring, and specialized nursing.
• Standardized pathways reduce variability and enhance patient safety. Key components include:
  • Standardized mapping tasks and rehearsal
  • Predefined airway rescue and seizure protocols
  • Consistent, closed-loop communication between teams
  • Routine use of a scalp block
  • Clear criteria for conversion to GA

Anesthetic Techniques

AC is typically performed using one of two strategies:

• Monitored Anesthesia Care (MAC) uses variable degrees of continuously titrated sedation. During stimulating phases, the sedation may be deepened for comfort while maintaining natural airway and spontaneous ventilation. Sedation is reduced or withheld to facilitate patient cooperation during brain mapping. There is usually a smooth transition from deeper levels of sedation to awakening.
• Sleep–Awake–Sleep (SAS) begins with induction of GA and placement of an artificial airway – typically a supraglottic airway, or less often an endotracheal tube – before the start of surgery. This is followed by controlled emergence and removal of the artificial airway once the patient can protect their airway, in preparation for brain mapping. On completion of the mapping, the patient is re-sedated, with or without an artificial airway, for closure. While an artificial airway offers greater control, these transitions may be challenging and require precise timing.
• Despite their differences, both approaches depend on a high-quality scalp block, which provides essential anesthesia and allows neurological mapping in an awake patient. A key distinction between SAS and MAC is whether an artificial airway is used or not. Airway management is particularly challenging when the patient’s head is pinned to the operating room table. Preparing for airway emergencies and potential conversion to GA is emphasized^1-3,5 (Table 1).

Drug Regimens

• Medication regimens must accommodate the differing demands of MAC and SAS.
• In MAC, dexmedetomidine or carefully titrated propofol is used to provide light, cooperative sedation while preserving spontaneous ventilation.¹¹
• In SAS, anesthetics must support deep anesthesia for opening and closure yet allow a timely, predictable emergence for mapping; propofol is commonly used, and remimazolam offers a promising alternative for rapid transitions.¹⁰
• Multimodal analgesia, often including low-dose remifentanil, is frequently added. Choosing the optimal regimen requires experienced clinical judgement and an ability to anticipate case-specific needs. It is regarded by some experts as more of an art than a science (Table 2).

Scalp Block

• Scalp block is the principal anesthetic modality for AC regardless of whether MAC or SAS is chosen.
• Targets include supraorbital, supratrochlear, auriculotemporal, zygomaticotemporal, and occipital nerves (Figure 1).
• The greater occipital nerve may be more accurately targeted using ultrasound guidance; other nerves are reliably blocked using landmark techniques.
• A well-executed block enhances mapping quality, reduces movement and hemodynamic swings, and improves patient satisfaction.
• Long-acting local anesthetics (e.g., bupivacaine, ropivacaine) are commonly used. Careful attention to dose is needed to avoid local anesthetic systemic toxicity.

Intraoperative Complications and Management

Common complications include:^1-3

• Airway Obstruction or Hypoventilation: Occurs primarily under MAC anesthesia when excessive sedation is used. It can be prevented by careful titration and the use of a scalp block to reduce the need for sedatives.
• Seizures: Cortical mapping using electrical stimulus may provoke seizures; cold saline irrigation and small propofol boluses remain standard abortive measures. Seizure prophylaxis using antiseizure medications is essential for all ACs. (e.g., levetiracetam bolus before incision).
• Pain and Discomfort: All patients reported some pain, most commonly associated with pinning, drilling, and positioning.⁶ Scalp block significantly mitigates discomfort and is considered the primary anesthetic for AC success. An additional local anesthetic field block by the surgeon may be necessary.
• Anxiety and Emotional Intolerance: Preoperative cognitive deficits and low performance status are major predictors of emotional intolerance.⁵ Preparedness and continuous intraoperative reassurance are protective. Patients felt that participating in AC gave them a sense of control over their disease and increased their trust in the treatment team.⁶

Outcomes

• Neurologic and Oncologic Outcomes
  • AC as compared with craniotomy under GA offers superior functional outcomes in tumor surgery involving eloquent regions (GLIOMAP study).⁴
• Patient-Reported Outcomes
  • Most patients report satisfactory experiences and would choose AC again.⁶
  • MAC and SAS yield similar subjective experiences.⁸
• Procedural Efficiency
  • MAC consistently results in shorter operative times than SAS.^7-9