AWAKE CRANIOTOMY AND SCALP BLOCK

MD Anaesthesia PG Examination - Major Answer (30 Marks)

PART I: AWAKE CRANIOTOMY

1. Definition and Concept

2. Indications

• Tumour surgery near eloquent cortex: lesions adjacent to motor strip, speech areas (Broca's/Wernicke's), or sensory cortex
• Low-grade gliomas in or near language areas (dominant hemisphere) - evidence confirms awake mapping improves extent of resection with better neurological outcomes [PMID: 41398134, Systematic Review, 2025]
• Epilepsy surgery - resection of epileptic foci close to eloquent cortex; temporal lobe epilepsy with mesial involvement
• Deep brain stimulator placement (electrode testing)
• Resection of arteriovenous malformations near eloquent cortex

3. Contraindications

• Patient refusal
• Inability to cooperate (intellectual disability, severe anxiety, claustrophobia, psychosis)
• Paediatric age (generally not suitable below 10-12 years)
• Severe obstructive sleep apnoea (airway management impossible in fixed head)
• Language barrier (inability to communicate effectively)

• Obesity (compromised airway, position intolerance)
• Chronic pain requiring high opioid doses
• Raised ICP with impending herniation
• Severe hearing/visual impairment (prevents testing)
• Uncontrolled seizures

4. Patient Selection and Preoperative Preparation

• Detailed psychological evaluation: assess anxiety levels, claustrophobia, cooperation ability
• Neuropsychological baseline: speech, motor, and cognitive assessment by a neuropsychologist
• Explanation of procedure: step-by-step description of what the patient will experience - this is the cornerstone of patient cooperation
• Practice runs: have the patient perform the tasks they will be asked to do intraoperatively (name objects, move hand, count)
• Optimise analgesia: address any pre-existing pain
• Anticonvulsants: if electrocorticography (ECoG) is planned, reduce or discontinue anticonvulsants as benzodiazepine premedication is avoided (interferes with EEG localisation)
• Antiemetic prophylaxis planning

• Anxiolytics used cautiously (benzodiazepines avoided if ECoG planned)
• Anticonvulsants adjusted per surgical plan
• Dexamethasone for brain oedema prophylaxis

5. Anaesthetic Techniques

A. Monitored Anaesthesia Care (MAC) / Sedation-Only Technique

• Patient sedated throughout with spontaneous ventilation and unprotected airway
• Sedation depth titrated: deeper during painful phases (pin placement, skin incision, craniotomy), lighter during mapping
• Most popular for less invasive approaches

B. Asleep-Awake-Asleep (AAA) Technique

• Patient anaesthetised with LMA or ETT for initial craniotomy phase
• Airway device removed when brain is exposed (after dural opening)
• Patient awakens for cortical mapping
• Reanaesthetised and airway re-established for dural closure and skin closure
• LMA (particularly ProSeal or i-gel) preferred over ETT due to ease of insertion and removal

C. Conscious Sedation (Awake Throughout)

• Patient mildly sedated for all phases; no deep anaesthesia
• Scalp block is the primary analgesic technique

6. Drug Regimens for Sedation

Propofol (most commonly used)

• Target-controlled infusion (TCI) or manual infusion 25-75 mcg/kg/min
• Provides rapid titration, fast recovery
• Must be discontinued at least 15 minutes before EEG recording - it leaves a residual high-frequency beta activity that obscures abnormal EEG activity

Remifentanil

• Infusion at 0.02-0.05 mcg/kg/min, often combined with propofol
• Ultra-short-acting; provides analgesia during painful phases
• Risk: respiratory depression (synergistic with propofol) - requires vigilant monitoring

Dexmedetomidine (DEX) - increasingly preferred

• Alpha-2 agonist: sedation + anxiolysis + analgesia with minimal respiratory depression - key advantage
• Infusion: 0.1-0.5 mcg/kg/h during neurocognitive testing; loading dose 0.5-1 mcg/kg over 10 min
• Satisfactory conditions for speech mapping and ECoG reported at 0.1-0.2 mcg/kg/h during testing
• [PMID: 39079421, Meta-Analysis 2024]: DEX for awake craniotomy - lower respiratory depression vs propofol-remifentanil with comparable mapping efficacy
• Disadvantage: delayed recovery of responsiveness at higher doses

Propofol + Dexmedetomidine combination

• Dexmedetomidine as background infusion reduces propofol requirements
• Beneficial combination for longer procedures

Ketamine

• Low-dose ketamine (0.1-0.3 mg/kg IV) can be used as analgesic adjuvant
• Maintains airway reflexes; risk of dysphoria and hallucinations at higher doses

7. Intraoperative Monitoring

• Standard ASA monitors: ECG, SpO2, NIBP, temperature
• Arterial line (mandatory): continuous BP monitoring; arterial blood gases to detect hypercapnia
• Capnography: essential if deep sedation planned - confirms airway patency and respiratory drive breath by breath; end-tidal CO2 via nasal prongs
• Urinary catheter for long procedures
• EEG/electrocorticography (ECoG) setup
• Neuropsychological testing team presence

8. Painful Phases of Awake Craniotomy

9. Intraoperative Management Pearls

• Head positioning: maximise neck flexion and atlanto-occipital extension before final head holder lockdown - this widens the margin for safe sedation with spontaneous ventilation. Once fixed, airway access is severely restricted
• Surgical drape: positioned to maintain direct, constant visual access to the patient's face (for speech testing, motor observation, and patient communication)
• Temperature management and pressure area padding: critical for long procedures; patient comfort = patient cooperation
• Communication: constant verbal reassurance throughout; explain each step

10. Cortical Mapping

• Surgeon applies bipolar electrical stimulation probe to the cortical surface
• Patient performs real-time neuropsychological tasks: naming objects, counting, moving limbs
• Positive mapping: stimulation causes interruption/abnormal response = eloquent cortex = no-resection zone
• Negative mapping: no response = safe to resect
• Speech (language) areas: predominantly left hemisphere (posterolateral temporal cortex, inferior frontal gyrus - Broca's area)
• Motor strip: pre-central gyrus; sensory strip: post-central gyrus

11. Complications of Awake Craniotomy

Intraoperative

1. Intraoperative seizures - most common intraoperative complication

• Treatment: surgeon irrigates cortex with cold (ice-cold) saline first
• Propofol bolus 20 mg IV (Barash) or increments of 0.5-1.0 mg/kg (Miller)
• If persistent: phenytoin/levetiracetam IV

1. Airway obstruction / respiratory depression - particularly dangerous in fixed head position
2. Uncooperative or disinhibited patient ("awake patient failure") - anxiolysis, reassurance, may need conversion to GA
3. Oversedation prohibiting neuropsychological testing
4. Brain swelling / intractable oedema - poor surgical conditions
5. Local anaesthetic systemic toxicity (LAST) - cumulative from scalp block + dural infiltration + surgeon's field block
6. Pain - inadequate scalp block, surgical stimulation of dura
7. Nausea and vomiting - routine antiemetics (ondansetron, dexamethasone) recommended

Postoperative

• Neurological deficit (transient or permanent)
• Cerebral oedema
• Haematoma
• Infection
• Post-procedure anxiety/PTSD

PART II: SCALP BLOCK

1. Concept and Importance

2. Anatomy of Scalp Innervation

A. Branches of the Trigeminal Nerve (CN V) - Anterior/Lateral Scalp

B. Cervical Spinal Nerves (C2-C3) - Posterior Scalp

3. Techniques of Scalp Block

Option A: Individual Nerve Block Technique (Selective/Classic)

• Landmark: superomedial aspect of orbit, medial to supraorbital notch, near trochlea
• Technique: 2-3 mL LA injected subcutaneously at medial end of eyebrow / superomedial orbital rim

• Landmark: supraorbital notch/foramen (palpable on superior orbital rim, approximately in line with the pupil)
• Technique: 3-5 mL LA injected at notch/foramen; needle directed superiorly

• Landmark: lateral orbital rim / temporal fossa, just lateral to zygomaticofrontal suture line
• Technique: 2 mL LA injected subcutaneously in temporal fossa above the zygomatic arch

• Landmark: pre-auricular region, 1.5 cm anterior to the tragus, at the level of the zygomatic arch
• Technique: 3 mL LA injected subcutaneously anterior to the tragus (caution: superficial temporal artery nearby)

• Landmark: nuchal line; palpate the occipital artery at the superior nuchal line - the greater occipital nerve lies medial to the occipital artery, approximately one-third of the way from the external occipital protuberance to the mastoid process
• Technique: 3-5 mL LA injected medial to the pulsating occipital artery, aspirate first (close to artery)

• Landmark: 2.5-3.5 cm lateral and 1-2 cm caudal to the greater occipital nerve at the nuchal line
• Technique: 2-3 mL LA injected subcutaneously at this point

• Landmark: posterior to the ear, at the mastoid process
• Technique: 2-3 mL LA injected subcutaneously posterior to the auricle/mastoid region

Option B: Circumferential Ring Block Technique (Field Block)

• A practical alternative requiring less anatomical precision
• A ring of local anaesthetic is infiltrated circumferentially above an imaginary line drawn from the external occipital protuberance to the eyebrows, passing along the upper border of the ear
• This line encircles all nerve entry points into the scalp
• All scalp nerves become superficial and accessible above this line
• Volume required: approximately 30 mL of LA solution (with epinephrine 1:200,000)
• Injections made subcutaneously using a long 22-gauge needle advanced along the scalp

4. Local Anaesthetic Choice and Dosing

• Mandatory addition (unless contraindicated)
• Vasoconstriction reduces bleeding, decreases systemic absorption, prolongs block duration
• Alerts to inadvertent intravascular injection (tachycardia)

5. Local Anaesthetic Toxicity - Critical Concern

• Scalp block by anaesthesiologist
• Pin site infiltration (4-6 pin sites) by anaesthesiologist/surgeon
• Dural infiltration by surgeon (dura is pain-sensitive)
• Incision field block by surgeon

• Track cumulative LA dose throughout the procedure
• Communicate with surgeon regarding remaining safe dose
• Use maximum doses: Bupivacaine with adrenaline = 3 mg/kg (max ~225 mg in 70 kg adult)
• Ropivacaine with adrenaline = 3.5-4 mg/kg
• Lidocaine with adrenaline = 7 mg/kg

6. Additional Pin Site and Dural Analgesia

• Pin sites (Mayfield clamp): 5-10 mL of 1% lidocaine or 0.25% bupivacaine infiltrated at each pin site before application - this is the most acutely painful moment
• Dural infiltration: surgeon infiltrates dura directly, especially the middle meningeal artery region and along subtemporal dura (most pain-sensitive portion)
• Periosteal infiltration: along incision line before skin incision

7. Timing of Scalp Block

• Performed before skin preparation and head pinning
• Allow adequate onset time before pin placement (10-15 minutes for bupivacaine)
• Can be performed bilaterally (unilateral block for unilateral craniotomy; bilateral if required)
• Often performed while patient is lightly sedated to improve comfort during injection

8. Advantages of Scalp Block in Awake Craniotomy

1. Reduces intraoperative pain and sedation requirements
2. Attenuates haemodynamic responses to painful stimuli (pin insertion, skin incision)
3. Reduces propofol and opioid consumption - better neurological testing conditions
4. Reduces brain swelling (less coughing, less sympathetic stimulation → less ICP elevation)
5. Reduces postoperative pain - scalp block with LA significantly reduces post-craniotomy pain scores (Miller's Anesthesia)
6. Reduces PONV (reduced opioid use)
7. Facilitates earlier recovery and mobilisation

9. Complications of Scalp Block

PART III: INTEGRATED ANAESTHETIC PLAN FOR AWAKE CRANIOTOMY

Step-by-Step Protocol

1. Thorough counselling and consent
2. NPO as standard
3. Establish IV access (large bore), arterial line
4. Antiemetic prophylaxis: dexamethasone 8 mg + ondansetron 4 mg
5. Urinary catheter

1. Propofol TCI or infusion (± dexmedetomidine loading 0.5-1 mcg/kg over 10 min)
2. Insert LMA (AAA technique)
3. Patient positioned with adequate padding, face visible
4. Scalp block performed: all 6-7 nerves blocked; pin site infiltration
5. Allow 15 min onset time
6. Head pinned (Mayfield), head positioned

1. Propofol discontinued (at least 15 min before EEG)
2. LMA removed (AAA) or sedation lightened (MAC)
3. Dexmedetomidine at 0.1-0.2 mcg/kg/h if continued
4. Neuropsychological testing + cortical mapping by surgeon
5. Cold saline available at field for seizure management
6. Propofol bolus 20 mg at hand for seizure management

1. Propofol/remifentanil infusion restarted
2. LMA re-inserted (AAA)
3. Surgical closure
4. Emergence, PACU/ICU as per standard craniotomy protocol

Summary Table: Key Points for Exam

• Miller's Anesthesia, 10th Ed. (Elsevier) - Awake Craniotomy and Seizure Surgery, Ch. 53; Scalp Blocks, Ch. 74
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9th Ed. - Awake Craniotomy
• Roberts & Hedges' Clinical Procedures in Emergency Medicine - Scalp Block Technique
• [PMID 39079421] Akavipat et al. Dexmedetomidine for awake craniotomy: Systematic Review & Meta-Analysis. J Clin Neurosci. 2024
• [PMID 41398134] Sadhasivam et al. Awake mapping and outcomes in low-grade gliomas: Systematic Review. Neurosurg Rev. 2025