Anesthetic Considerations in Supratentorial Craniotomy

🔹 Introduction

Supratentorial craniotomy refers to surgical procedures involving the cerebral hemispheres above the tentorium cerebelli, typically performed for tumors, epilepsy, vascular lesions, or trauma.

✅ Common Indications

• Gliomas (low and high-grade)
• Meningiomas
• Metastatic lesions
• Epilepsy surgery
• Aneurysm clipping (anterior circulation)
• Cortical AVMs
• Trauma-related hematoma evacuation

The anesthetic management aims to ensure:

• Optimal surgical exposure
• Hemodynamic and ICP control
• Neuroprotection
• Rapid and smooth emergence for neurological assessment

🔹 Preoperative Assessment

1. Neurological Status

• GCS, focal deficits, signs of raised ICP (headache, vomiting, papilledema)
• Seizure history (antiepileptic use)

2. Imaging Review

• CT/MRI for lesion location, mass effect, midline shift
• Evaluate ventricular size, edema, herniation signs

3. Medications

• Steroids (e.g., dexamethasone for edema)
• Antiepileptics (phenytoin, levetiracetam)
• Antihypertensives

4. Comorbidities

• Hypertension, diabetes, CAD
• Evaluate airway (possible difficult airway in skull base tumors)

🔹 Goals of Anesthesia

• Maintain cerebral perfusion pressure (CPP): CPP = MAP – ICP
• Avoid increases in ICP
• Provide a relaxed brain for optimal surgical access
• Facilitate neurophysiological monitoring (when needed)
• Allow for rapid emergence for neurological evaluation

🔹 Intraoperative Considerations

🔸 1. Monitoring

✅ Standard Monitoring

• ECG, NIBP, SpO₂, EtCO₂, temperature

✅ Advanced Monitoring

• Arterial line: Beat-to-beat BP and ABGs
• CVP line: For large tumors, mannitol response
• ICP monitoring: In select cases
• Neuromonitoring: SSEP, MEP, EEG (especially in eloquent cortex lesions)
• Urine output: Especially with osmotic diuretics

🔸 2. Anesthetic Technique

✅ Induction

• Smooth, avoid coughing or bucking
• Agents: Propofol, etomidate, or thiopentone
• Short-acting opioids (fentanyl/remifentanil)

Avoid ketamine (↑CBF, ↑ICP)

✅ Airway

• Secure with oral ETT, fixed well to prevent dislodgement during positioning
• May need reinforced tube for head fixation

✅ Maintenance

• Balanced anesthesia:
• TIVA (propofol + remifentanil) preferred if evoked potentials used
• Volatile agents: Isoflurane, sevoflurane (<1 MAC) if monitoring not used
• Muscle relaxation: Avoid during MEP monitoring
• Avoid N₂O: Increases CBF, risk of air embolism
• Controlled ventilation to maintain EtCO₂ ~ 30–35 mmHg (mild hyperventilation)

🔸 3. Positioning

• Common: Supine or lateral, with head fixed in Mayfield clamp
• Padding of pressure points essential
• Head elevated ~15–30° to promote venous drainage and reduce ICP

Ensure neck is not kinked → impaired venous outflow → ↑ICP

🔸 4. Brain Relaxation Strategies

✅ Pharmacologic

• Mannitol 0.25–1 g/kg IV
• Furosemide adjunct
• Steroids (for tumors, not trauma)
• Propofol or barbiturates (decrease CMR and ICP)

✅ Physiologic

• Head elevation
• Controlled ventilation (PaCO₂ ~30–35 mmHg)
• Avoid hyperthermia

🔸 5. Fluid and Hemodynamic Management

• Maintain euvolemia
• Prefer isotonic crystalloids (NS, balanced salt solutions)
• Avoid glucose-containing fluids → risk of hyperglycemia and worsened ischemia
• Colloids: used cautiously
• Blood loss replacement guided by monitoring

Avoid hypotension: CPP = MAP – ICP; ensure adequate MAP at all times

🔸 6. Temperature Management

• Maintain normothermia
• Hypothermia affects coagulation, emergence
• Hyperthermia increases cerebral metabolic rate (CMRO₂)

🔸 7. Emergence and Extubation

Goals:

• Smooth, controlled, rapid emergence for neuro exam
• Avoid coughing, bucking, agitation → ↑ICP, risk of hemorrhage

Techniques:

• Use short-acting agents (TIVA)
• Consider deep extubation in selected patients
• Reversal of NMB + full awake state + hemodynamic stability essential

🔹 Special Considerations

✅ Awake Craniotomy

• For tumors near eloquent cortex (motor, language areas)
• Requires:
• Asleep–awake–asleep or awake throughout technique
• Scalp block, conscious sedation (dexmedetomidine, remifentanil)
• Continuous neuro exam during resection

✅ Seizure Prophylaxis

• Perioperative antiepileptics (phenytoin, levetiracetam)
• Avoid agents that lower seizure threshold (e.g., enflurane)

✅ VTE Prophylaxis

• Sequential compression devices
• LMWH delayed 24 hrs post-op if no bleeding

✅ DVT Risk

• Reduced mobility, tumor-induced hypercoagulability

🔹 Postoperative Care

• Close monitoring in ICU or HDU
• Serial neurological exams
• ICP and CPP monitoring in selected patients
• Pain control: IV opioids, NSAIDs cautiously (if no bleeding risk)
• Monitor for:
• Rebleed
• Seizures
• Electrolyte imbalance (esp. SIADH or DI)
• CSF leaks or pneumocephalus

✅ What Makes Supratentorial Craniotomy Anesthetically Unique?

1. Proximity to Eloquent Cortex

• Lesions often lie near language (Broca’s/Wernicke’s), motor, or sensory cortices
• → Requires intraoperative neurophysiological monitoring (SSEP, MEP)
• → May require awake craniotomy with patient cooperation

This is unlike infratentorial surgery (brainstem, cerebellum) where such mapping is rarely needed.

2. Awake Craniotomy is Common

• Often done to maximize tumor resection while preserving function
• Demands:
• Patient cooperation
• Precise sedation titration
• Impeccable airway and hemodynamic control

Rarely done for infratentorial cases due to anatomical constraints and risk of brainstem compromise.

3. Positioning Risks are Lower — but Still Important

• Usually supine or lateral position
• Less risk of venous air embolism than sitting posterior fossa position
• But still must ensure neutral neck → avoid venous congestion → ↓ICP

4. Focus on Cerebral Protection, Not Cranial Nerve Function

• Unlike posterior fossa surgery (brainstem, cranial nerves), supratentorial craniotomy emphasizes:
• CMRO₂ control
• ICP and CPP regulation
• Preventing seizures

No cranial nerve monitoring needed here (no IX–XII risk).

5. Brain Relaxation is More Critical for Surgical Exposure

• The craniotomy flap is typically smaller
• Surgeons require a soft, relaxed brain to access deep lesions
• → More aggressive use of:
• Mannitol
• Hyperventilation
• Diuretics
• Propofol burst suppression (in selected cases)

6. High Risk of Postoperative Seizures

• Supratentorial lesions are closer to cortex → higher epileptogenic potential
• Perioperative seizure prophylaxis more critical than infratentorial lesions

7. Rapid Emergence is Critical

• To check:
• Limb strength
• Language function
• Consciousness
• Delayed emergence = concern for hematoma, edema, ischemia

Posterior fossa patients may remain ventilated longer due to brainstem proximity.

🔸 Practical Differences: Supratentorial vs Infratentorial Craniotomy

When Supratentorial Craniotomy Becomes “Special”: Clinical Examples

1. Left Temporal Lobe Tumor

• Near language areas → awake craniotomy, speech testing
• Anesthetic must allow:
• Sedation → awake → sedation cycle
• Zero coughing or movement

2. Deep-Seated Insular Glioma

• High risk of edema, vascular injury
• ICP control paramount
• May use advanced neurophysiologic monitoring

3. Frontal AVM

• Can bleed during manipulation
• Requires tight MAP control, volume status, and neuro-monitoring

📝 Viva Tip

Q: What is the hallmark of anesthesia in supratentorial craniotomy?

A: Optimizing cerebral conditions (CPP, ICP), ensuring a relaxed brain, enabling neurophysiological monitoring or awake mapping, and achieving rapid emergence for post-op neuro assessment.

🔍 Suggested References

1. Miller’s Anesthesia, 9th Edition – Chapter on Craniotomy
2. Cottrell and Young’s Neuroanesthesia – Supratentorial tumor anesthesia
3. BJA Review Articles – Advances in neuroanesthesia
4. StatPearls – Craniotomy Anesthesia
5. WFSA – Neuroanesthesia modules