Awake Craniotomy - Anesthesia Implications in Detail

1. Definition and Rationale

• Motor function (primary motor cortex, corticospinal tract)
• Speech/language (Broca's area, Wernicke's area - usually left hemisphere)
• Sensory function (primary somatosensory cortex)
• Memory (mesial temporal structures)

2. Patient Selection and Preoperative Assessment

• Psychologically motivated and non-claustrophobic
• Able to understand and follow instructions
• No severe anxiety disorder or cognitive impairment
• No uncontrolled movement disorder (tremor, dyskinesia)
• No morbid obesity or known difficult airway
• No language barriers that complicate testing

• Thorough neuropsychological baseline assessment (speech, motor, sensory)
• Detailed explanation of each phase of the procedure: duration, what the patient will feel, what they will be asked to do, and what their limitations on movement will be
• Discussion of potential uncomfortable phases: pin fixation, craniotomy, dural manipulation (especially subtemporal dura - painful)
• If intraoperative electrocorticography (ECoG) is planned, anticonvulsants are often reduced by half or discontinued to avoid suppressing seizure activity needed for localization
• Benzodiazepine premedication is contraindicated if EEG localization of seizure foci is intended, as they suppress the abnormal EEG activity being sought
• Anxiolytics may still be used in non-EEG cases with caution

"A motivated patient is critical to the success of the procedure. Preoperative assessment should include a detailed explanation of the anesthetic so as to ensure cooperation and allay anxiety." - Barash Clinical Anesthesia 9e

3. Anesthetic Techniques

A. Monitored Anesthesia Care (MAC) Throughout

B. Asleep-Awake-Asleep (AAA) Technique (most commonly used)

• Phase 1 (Asleep): General anesthesia or deep sedation for positioning, head fixation, scalp infiltration, craniotomy, and dural opening. A supraglottic airway device (LMA/SLMA) is typically used. Some groups use an endotracheal tube with a custom design.
• Phase 2 (Awake): The airway device is removed once the brain surface is exposed. The patient is woken and cooperative testing (language, motor, sensory) is conducted.
• Phase 3 (Asleep): Airway device is reinserted and anesthesia re-induced for tumor resection and closure.

"Awake craniotomy can be performed with the patient sedated for the duration of the procedure, or with an 'asleep-awake-asleep' technique employing a supraglottic airway device." - Barash 9e

C. Conscious Sedation Throughout

4. The Local Anesthetic Technique - The Foundation

"The essential element of an anesthetic for an awake craniotomy is the local anesthetic technique. Sedation cannot compensate for inadequate anesthesia of the scalp." - Miller's Anesthesia 10e

Scalp Nerve Block

Fig. 53.19 - The cutaneous nerves of the scalp (Miller's Anesthesia 10e)

• Short procedures: 1% mepivacaine
• Prolonged procedures: 0.75% ropivacaine
• Epinephrine-containing solutions are preferred for vasoconstriction and prolongation of block

"The volume of local anesthetic used to infiltrate pin sites and perform the scalp nerve blocks can be substantial. It is appropriate for the anesthesiologist to keep track of, and provide advice about, the doses of local anesthetics used." - Miller's Anesthesia 10e

5. Sedation Agents - Detailed Pharmacology

Propofol

• Most widely used; provides titratable, predictable sedation
• Rapid awakening facilitates quick transition to the awake phase
• Must be discontinued at least 15 minutes before EEG recording - leaves a residual high-frequency, high-amplitude beta activity footprint on the EEG that obscures abnormal seizure activity
• When seizures occur during cortical stimulation, small boluses of propofol (0.5-1.0 mg/kg IV, or 20 mg bolus) are used to terminate them - but should be withheld briefly to allow spontaneous termination since propofol interferes with subsequent EEG localization

Remifentanil

• Ultra-short-acting opioid; complements propofol for painful phases
• Infusion rate: 0.02-0.05 mcg/kg/min
• Synergistic respiratory depression with propofol - the most significant danger in a patient with a fixed, inaccessible airway (head in pin fixation)

Dexmedetomidine

• Highly selective alpha-2 adrenergic agonist
• Provides sedation + anxiolysis + analgesia with minimal respiratory depression - its key advantage
• Increasingly the preferred agent, especially as a sole or primary drug
• Effective infusion range during testing: 0.1-0.5 mcg/kg/h
• Does not suppress spontaneous seizure activity at lower doses - suitable when ECoG is planned
• Allows satisfactory conditions for brain stimulation speech mapping and ECoG
• Limitation: may cause delays in achieving adequate patient responsiveness (slower onset/offset than propofol)
• Meta-analysis (PMID: 39079421, 2024) confirms dexmedetomidine provides equivalent sedation and mapping conditions with significantly lower rates of respiratory depression compared to propofol-remifentanil

"Dexmedetomidine is the agent of choice for sedation of patients undergoing awake craniotomies." - Morgan & Mikhail Clinical Anesthesiology 7e

Agent Combinations

• Propofol + remifentanil: effective but higher respiratory depression risk
• Propofol + dexmedetomidine: useful combination balancing depth with respiratory safety
• Dexmedetomidine + remifentanil: increasingly used
• Benzodiazepines: generally avoided - highest potential to interfere with EEG recording and seizure focus localization; also long duration

Monitoring Sedation Depth

• Standard ASA monitors
• Capnography is essential - provides breath-by-breath confirmation of airway patency and respiratory drive if deep sedation is used at any phase
• BIS monitoring may help titrate sedation
• An arterial catheter is routinely placed for beat-to-beat hemodynamic monitoring and blood gas sampling

6. Airway Management

• The patient's head is turned and fixed in a rigid pin head-holder
• The surgical drape obscures most of the patient's body
• Emergency intubation in this position is extremely difficult

• Positioning optimization is critical before sedation begins: maximize neck flexion and atlanto-occipital extension so the anesthesiologist retains the widest latitude to sedate while maintaining spontaneous ventilation
• The surgical drape must be positioned to allow direct, constant visual access to the patient's face - for airway monitoring AND to present naming/speech test images
• Hypoventilation and hypercapnia are detrimental - CO2 retention causes cerebral vasodilation and brain swelling, worsening surgical exposure
• Apnea requiring emergency intubation in a patient in a rigid head holder is a potentially catastrophic complication

7. Cortical and Subcortical Mapping - Anesthesia Interface

How mapping works:

• Object naming / picture naming - for language cortex identification
• Counting or reading - speech arrest indicates language involvement
• Limb movement testing - for motor strip mapping
• Sensory responses - for sensory cortex mapping

ECoG (Electrocorticography) for seizure surgery:

• After dural opening, cortical surface EEG is recorded to locate the seizure focus
• If no spontaneous seizure activity is seen, provocative agents may be given:
  • Methohexital ~0.3 mg/kg - generally safe and effective
  • Etomidate 0.05-0.1 mg/kg - alternative
  • Alfentanil 30-50 mcg/kg bolus - used under general anesthesia
  • Remifentanil 2.5 mcg/kg bolus - reported effective
  • Hyperventilation - also activates seizure foci

Anesthesia implications during mapping:

• No propofol during EEG recording (residual beta footprint)
• Dexmedetomidine can continue at low rates during testing
• Ensure patient is fully responsive, communicating, and understands instructions
• Constant communication between anesthesiologist, surgeon, and neuropsychologist

8. Intraoperative Complications and Management

"Seizures should be treated with cold saline applied to the brain surface by the surgeon and a small bolus of propofol (20 mg) intravenously." - Barash 9e

9. Patient Positioning Considerations

• All padding and positioning must be completed before any sedation is given - the patient cannot reposition themselves once the head is fixed and sedation has started
• Common positions: lateral decubitus or supine with head turned
• Pressure areas, eye protection, arm padding
• Urinary catheter placement (procedures are typically 3-6 hours)
• Temperature management (warm blankets, forced air warming to prevent hypothermia and shivering during the awake phase)
• The anesthesiologist must be able to see the patient's face at all times from their position at the head of the bed

10. Monitoring

11. Postoperative Considerations

• Patients may be observed in PACU or ICU (similar to any craniotomy)
• Most patients tolerate sedation for surgical closure after the awake phase
• Analgesia: multimodal approach - scalp block provides good postoperative pain relief, supplemented with paracetamol/NSAIDs, opioids as needed
• Monitor for new neurological deficit (compare to intraoperative baseline)
• Seizure precautions continue postoperatively
• For patients who tolerated the procedure poorly or are poor awake candidates, surrogate testing under general anesthesia is an alternative for motor/sensory mapping - but language testing cannot be performed under GA

12. Special Considerations

Epilepsy Surgery vs. Tumor Surgery

• Epilepsy cases require discontinuation of anticonvulsants and avoidance of propofol before EEG recording
• Tumor cases primarily need language and motor mapping; ECoG is less central

Pregnant Patients

• Case reports exist; dexmedetomidine and mannitol have been used (PMID: referenced in Miller's - Handlogten et al., 2015)

Pediatric Patients

• Awake craniotomy in children is rare but feasible from age ~10-12 years; requires highly experienced teams and careful psychological preparation
• Meta-analysis (PMID: 37839565, 2024) shows comparable outcomes to adults in selected pediatric patients

Failed Awake Craniotomy

• If the patient becomes uncooperative or experiences an emergency, conversion to general anesthesia in the middle of the procedure with a head in a pin holder is technically very challenging and must be planned for

Summary: The Anesthesiologist's Core Priorities

1. Patient selection and preparation - Ensure a motivated, well-informed, cooperative patient
2. Perfect local anesthesia - Scalp nerve blocks are the cornerstone; sedation cannot substitute
3. Meticulous sedation titration - Match depth to the phase of the procedure
4. Airway vigilance - Capnography, constant visual access, pre-planned emergency rescue
5. Avoid LA toxicity - Track cumulative doses
6. Drug selection for ECoG - No benzodiazepines; stop propofol 15 min before EEG; dexmedetomidine preferred
7. Seizure preparedness - Cold saline first, propofol rescue second
8. Communication - Constant verbal contact with the patient throughout

• Miller's Anesthesia, 2-Volume Set, 10e, Chapter 53 (Neurosurgical Anesthesia) - Awake Craniotomy and Seizure Surgery
• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e, Chapter on Neuroanesthesia - Awake Craniotomy
• Morgan & Mikhail's Clinical Anesthesiology, 7e
• Akavipat et al. (2024) - Dexmedetomidine for awake craniotomy: Systematic review and meta-analysis [PMID: 39079421]
• Sadhasivam et al. (2025) - Awake mapping and extent of resection in low-grade gliomas [PMID: 41398134]
• Honeyman et al. (2025) - Awake vs asleep craniotomy for eloquent glioblastoma [PMID: 40887547]

• ☐ Checkboxes for every actionable item
• ⚠ Red warning markers on high-risk items (e.g., NO benzos before EEG, propofol stop 15 min before recording, LAST risk, emergency airway limitation)
• Dual-column layout throughout to maximize content density
• Scalp nerve block table with landmarks and territories
• Sedation drug table with loading doses, infusion rates, and key cautions
• Complication response table with first-line and escalation steps
• Footer citing Miller's 10e, Barash 9e, Morgan & Mikhail 7e