What is the recommended anesthetic management approach for patients undergoing suboccipital craniotomy and removal of infratentorial mass?

Anesthetic Management for Suboccipital Craniotomy and Infratentorial Mass Removal

The optimal anesthetic management for patients undergoing suboccipital craniotomy for infratentorial mass removal should follow neuroanesthetic principles that prioritize brain relaxation, excellent blood pressure control, and rapid emergence while maintaining euvolemia, normotension, isotonicity, normoglycemia, and mild hypocapnia. 1

Preoperative Considerations

• Optimize preexisting medical conditions
• Assess neurological dysfunction from the mass effect
• Ensure adequate blood products are available due to potential for significant blood loss
• Consider that 10% of patients with arteriovenous malformations (AVMs) harbor intracranial aneurysms that may increase rupture risk during blood pressure fluctuations 1

Anesthetic Technique

Induction

• Direct arterial pressure monitoring is indicated via arterial line placement 1
• Options for induction:
  • Propofol (1-2 mg/kg) with remifentanil (1 mcg/kg/min) 2
  • Thiopental with remifentanil or fentanyl 2
  • Etomidate for patients with poor cardiovascular reserve

Maintenance

Total Intravenous Anesthesia (TIVA) Approach

• TIVA using propofol and remifentanil offers advantages for intracranial surgery:
  • Decreases intracranial pressure (ICP)
  • Increases cerebral perfusion pressure
  • Provides better access to operative site 3
  • Remifentanil at 0.1-0.4 mcg/kg/min with propofol infusion 2

Volatile-Based Approach

• If using volatile anesthetics:
  • Maintain at low concentrations to avoid cerebral vasodilation
  • Isoflurane at end-tidal concentration of 0.5-0.6% 4
  • Avoid high inspired concentrations that may increase cerebral blood flow and ICP 1

Blood Pressure Management

• Maintain blood pressure that approximates patient's normal range 1
• For infratentorial surgery, induced hypotension may be useful during certain phases:
  • Decreases arterial pressure to facilitate surgical hemostasis
  • Choice of agent should be based on clinical context and practitioner experience 1
  • Options include remifentanil, propofol, or short-acting beta-blockers

Ventilation Strategy

• Mild hypocapnia (PaCO2 of ~35 mmHg) 1
• Avoid profound hypocapnia unless needed for control of brain swelling 1

Temperature Management

• Maintain normothermia or accept mild decrease in body temperature from anesthesia
• Do not aggressively rewarm until timing for emergence is planned 1
• Avoid postoperative hyperthermia as it may be detrimental 1

Positioning Considerations

• Careful positioning for suboccipital approach (prone or lateral)
• Protect pressure points, eyes, and peripheral nerves
• Ensure endotracheal tube is well secured
• Verify that venous drainage is not compromised

Monitoring

• Standard ASA monitors
• Direct arterial pressure monitoring
• Consider central venous access for large lesions or anticipated significant blood loss
• Consider ICP monitoring in selected patients 1
• Additional pulse oximeter on lower extremity if femoral access is used 1

Emergence and Recovery

• Plan for rapid emergence to allow for early neurological assessment
• Remifentanil-based TIVA may allow faster extubation compared to sufentanil-based regimens (6.4 vs 14.3 minutes) 5
• Anticipate and treat emergence hypertension, which is frequently encountered 1
• Be prepared for early postoperative analgesia, especially with remifentanil-based techniques 5

Special Considerations for Infratentorial Surgery

• Potential for brainstem manipulation requires vigilant hemodynamic monitoring
• Risk of air embolism in sitting position (if used)
• Cranial nerve monitoring may be required (avoid muscle relaxants if monitoring)
• Postoperative concerns include:
  • Airway edema
  • Cranial nerve dysfunction affecting swallowing/airway protection
  • Hydrocephalus requiring CSF drainage 1

Postoperative Management

• Close monitoring for signs of increased ICP or hydrocephalus
• Vigilant blood pressure control to avoid both hypo- and hypertension
• Careful attention to temperature control in the ICU 1
• Early neurological assessment to detect complications

Pitfalls to Avoid

• Inadequate blood pressure control during induction and intubation
• Excessive cerebral vasodilation from high concentrations of volatile anesthetics
• Inadequate depth of anesthesia during pin placement or incision
• Delayed emergence due to residual anesthetic effects
• Inadequate pain management in the immediate postoperative period
• Failure to anticipate and treat emergence hypertension

By following these principles, anesthetic management can be optimized to provide stable operating conditions while minimizing morbidity and mortality in patients undergoing suboccipital craniotomy for infratentorial mass removal.