Craniotomy for intracranial aneurysm

Craniotomy for intracranial aneurysm

Anesthesia type	General
Airway	ETT
Lines and access	PIV x2 Arterial line ± Central line
Monitors	Standard ASA 5-lead EKG Core temp UOP ABG ±CVP Neuromonitoring
Primary anesthetic considerations
Preoperative	Characterize neurologic deficits Controlled hypotension
Intraoperative	Smooth induction Controlled hypotension Have adenosine available Decrease CRMO2 Manage ICP
Postoperative	PONV
Article quality
Editor rating	Comprehensive
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A craniotomy for an intracranial aneurysm is a neurosurgical procedure performed to treat intracranial aneurysms to prevent or manage rupture, which can be life-threatening.

Overview

Background

• Intracranial aneurysms are defects of arterial walls which can occur at any of the major bifurcations of the Circle of Willis.
• The current AHA/American Stroke Association guidelines recommend that aneurysms which are amenable to treatment via either endovascular coiling or surgical clipping should be treated endovascularly.
• The perioperative risk varies greatly depending on whether the aneurysm has ruptured or not.
• The Hess and Hunt scale predicts mortality based upon exam findings:

Hunt-Hess Grading System for Aneurysmal Subarachnoid Hemorrhage
Grade	Description	Mortality
I	Asymptomatic, mild headache, slight neck stiffness	2%
II	Moderate-to-severe headache, neck stiffness, no neurologic deficit (other than cranial nerve palsy)	5%
III	Drowsiness, confusion, mild focal neurologic deficit	15-20%
IV	Stupor, moderate-to-severe hemiparesis	30-40%
V	Coma, decerebrate posturing	50-80%

Indications

• Complex aneurysms which cannot be definitively treated via endovascular coiling

Surgical procedure

• The procedure is performed through a craniotomy
• For cerebral aneurysms, approach is typically through the Sylvian fissure to expose the circle of Willis
• Aneurysms are treated using microsurgical clip ligation, which attempts to isolate defective aneurysmal wall and preserve flow through the vessel

Preoperative management

Patient evaluation

System	Considerations
Airway	If acute, consider RSI
Neurologic	Distinguish whether aneurysm has ruptured or not Identify any neurologic deficits Continue antiepilepetic agents
Cardiovascular	Evaluate baseline blood pressure If ruptured: May present with ST and T-wave changes, wall motion abnormalities, elevated troponin, and pulmonary edema Neurogenic stunned myocardium from catecholamines May be misdiagnosed as ACS

Labs and studies

• BMP
• CBC
• Coags
• Type and screen
• Brain MRI

Operating room setup

• Rapidly titratable vasoconstrictors and vasodilators in bolus syringes and infusions to acutely manage blood pressure
  • Phenylephrine or norepinephrine
  • Clevidipine (or nicardipine if clevidipine unavailable, though pharmacokinetics are less desirable)
• Adenosine (at least 1 mg/kg rapidly available)
• Osmotic agents (mannitol and/or hypertonic saline)
• Crossmatched blood should be available

Patient preparation and premedication

• Midazolam often beneficial to prevent anxiety-induced hypertension
• Consider aprepitant 40 mg PO or fosaprepitant 150 mg IV for PONV prophylaxis
• See hemodynamic management section below

Intraoperative management

Monitoring and access

• Standard ASA
• 5-lead ECG
• Core temperature
  • Consider bladder temperature monitoring if using mild hypothermia
• Arterial line
• 2 large bore IVs
• Consider central access
  • Rapid administration of vasoactives, adenosine
  • Peripheral vasoconstriction may limit drug delivery if using hypothermia
  • CVP monitoring, though added value is unclear
• Evoked potential monitoring
• EEG monitoring
• External ventricular drain may be useful for ICP monitoring and management if ruptured

Hemodynamic management

If ICP monitoring is available, maintain cerebral perfusion pressure 50-60 mmHg.

Unruptured aneurysms

• Preoperatively: Maintain blood pressure at or below patient's baseline.
• Intraoperatively: Target MAP 60-80 mmHg.
  • If hypertensive at baseline, baseline blood pressure may pose rupture risk once dura is opened and/or aneurysm is exposed (since transmural pressure gradient will increase)

Ruptured aneurysms

• Preoperatively:
  • Passive hypertension may represent beneficial reflex to maintain cerebral perfusion pressure in the setting of increased intracranial pressure, and should probably not be treated.
  • Hypertension due to noxious stimuli (i.e. pain, anxiety, disinhibition) should be avoided and appropriately treated depending on etiology (e.g. analgesics, anxiolytic, sedation).
• Intraoperatively: Target MAP 60-80 mmHg.

Induction and airway management

• Hemodynamically stable induction of general anesthesia and intubation is critical
  • Fentanyl, propofol, rocuronium, and +/- vasoactive agents to avoid hypo- and hypertension.

Positioning

• Pinned frame
• Position will depend on location of aneurysm
  • Supine with head turned commonly used if exposure achieved through the Sylvian fissure

Maintenance and surgical considerations

• Brain relaxation (hyperventilation, osmotic agents, CSF removal) should be used with caution in ruptured aneurysms
  • Decreased ICP can increase transmural pressure and increase risk of re-rupture/worsen bleeding
  • Risk/benefit should be discussed with surgeons
• Antibiotics (cefazolin 2-3 g)
• Dexamethasone (8-10 mg)
• ± Antiepileptics (levetiracetam 1 g)

Anesthetic maintenance

Anesthesia can be maintained safely using several techniques, and should be guided by provider experience, institutional practices, and unique patient considerations

• Many centers recommend the use of total intravenous anesthesia with propofol and remifentanil
  • Cerebral vasocontriction from propofol may be desirable
  • Limited interference with evoked potential monitoring
  • Antiemetic effect of propofol desirable
  • EEG monitoring essential to ensure drug delivery and allow dose titration
• Some centers use volatile anesthetics and/or nitrous oxide
  • Inhaled anesthetic somewhat mitigates risk of line infiltration and patient emergence/movement while in pinned frame
  • ≤0.5 MAC of volatile anesthetic will limit cerebral vasodilation, decoupling of autoregulation and interference with evoked potential monitoring
  • Consider risk of nitrous oxide expansion of pneumocephalus
• A combination of techniques can be used to leverage the benefits of each approach. For example:
  • Sevoflurane 0.5 MAC
  • Propofol 50-75 mcg/kg/min
  • Remifentanil 0.1-0.2 mcg/kg/min
  • Anesthetic and analgesic agents titrated using EEG

Temporary clipping

In some circumstances, surgeons may place a temporary clip proximal to the aneurysm to occlude flow and allow dissection and exposure without rupture. However, this can create focal ischemia distal to the clip/aneurysm. To minimize the risk of worsened neurologic outcomes, consider:

• Minimize temporary clip time
• Increase MAP (~90 mmHg) after clip placement to facilitate collateral perfusion
• Evoked potential monitoring to provide realtime feedback to surgeons
• Minimal evidence to support neuroprotective measures
  • Some providers still use induce burst suppression with a propofol bolus (~1 mg/kg) immediately prior to temporary clip placement due to the relative ease of rapid induction with minimal risk to hemodynamic stability
    • Concurrent bolus of vasoconstrictor often required to maintain stable MAP
  • Hypothermia not associated with improved outcomes during temporary clipping

Potential complications

Aneurysm rupture

Intraoperative aneurysm rupture can happen at any time until the aneurysm is clipped. Aneurysm rupture is a true emergency that requires rapid intervention.

If the aneurysm is exposed:

• Improve surgical visualization by decreasing/stopping bleeding rate to allow clip placement
  • Discuss with surgeons
  • Typically start with induced hypotension (MAP 50-60) using a short acting agent (e.g. clevidipine or esmolol)
  • If insufficient, consider inducing temporary flow arrest (asystole) using adenosine 0.3-0.6 mg/kg
    • If ineffective arrest achieved, double adenosine dose
    • Doses as high as 2 mg/kg have been reported as necessary
• Reduce CMRO2 with propofol 0.5-1 mg/kg bolus, increase infusion rate
• Resuscitate as indicated with IVF or blood products

If the aneurysm is not exposed and cannot be readily clipped:

• Intraoperative rupture without exposure can be difficult to detect
  • Be suspicious of this possibility with unexplained hypertension and bradycardia
• Ensure CPP is optimized between CPP 50 to 70 mmHg, generally this would require increasing the MAP.
  • Despite ongoing bleeding, brain perfusion is still critical
• Ensure adequate oxygenation and ventilation
• Consider decreasing ICP with head elevation, mannitol, or hypertonics if concern for critical ICP, though this may worsen bleeding

Emergence

• After clipping, normotension (MAP 70-90) is typically preferred
• Goals are similar to other neurosurgical procedures, including a smooth emergence, avoiding hypertension, coughing, and straining
• Intraoperative medications should be titrated down to allow for a rapid return to consciousness to permit neurologic examination prior to leaving the operating room

Postoperative management

Disposition

• ICU for neuro checks
• Postoperative CT/MRI
• If ruptured, risk of vasospasm highest 3-8 days after rupture

Pain management

• Consider scalp block prior to emergence
• Acetaminophen