Craniotomy for intracranial vascular malformations

Craniotomy for intracranial vascular malformations

Anesthesia type	General
Airway	ETT
Lines and access	Large bore IV x2 Arterial line ± Central line (if arterial nidus)
Monitors	Standard 5-lead ECG Core temp UOP ABG ± CVP (if arterial nidus) Neuromonitoring
Primary anesthetic considerations
Preoperative	Characterize neurologic deficits
Intraoperative	Smooth induction Hemodynamic goals vary Hypotension ↑ risk of steal If arterial nidus: Hypertension ↑ risk of rupture Have adenosine available Decrease CRMO2
Postoperative	Avoid hypertension after excision (risk of hyperemia)
Article quality
Editor rating	Comprehensive
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A craniotomy for intracranial vascular malformations is a neurosurgical procedure performed to remove vascular malformations which are considered high risk for rupture or produce neurologic symptoms.

Overview

Background

• Intracranial vascular malformations are congenital defects
• Typically present in young adulthood (most commonly 15-40 years old)
• Wide anatomic variability
  • High-flow arteriovenous malformations (AVM)
  • Low-flow angiographically occult vascular malformations (AOVM)
    • Cavernous malformations
    • "Cryptic" AVMs
    • Capillary telangiectasias
    • Transitional malformations
  • Low-flow venous angiomas
• Patients may be symptomatic or asymptomatic
• AVM may have be ruptured or unruptured and can be associated with vasospasm. Can also co exist with aneurysms. Most patients will have anesthesia for preoperative embolization of the AVM.

Indications

• The Spetzler-Martin AVM grading system estimates morbidity and mortality of surgery

Spetzler-Martin AVM grading scale

Supplemental AVM grading scale

Preoperative management

Patient evaluation

System	Considerations
Airway	If acute, consider RSI
Neurologic	Unruptured vs. ruptured important for risk stratification. Neurologic symptoms and mental status, signs and symptoms of elevated ICP, seizures
Cardiovascular	If acutely ruptured, can be associated with hypertension as well as other cardiac abnormalities including ischemia, arrhythmias, left ventricular dysfunction, and pulmonary edema.
Hematologic	Anemia

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, nitroprusside, or nitroglycerine. Nicardipine less desirable intraoperatively given longer pharmacokinetics.
• 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 for additional PONV prophylaxis
• See hemodynamic management section below

Regional and neuraxial techniques

• Consider postoperative scalp block for analgesia

Intraoperative management

Overall Goals

Goals are to provide a stable hemodynamic anesthetic along with reducing/normalizing the ICP and maintaining adequate CPP (at least 60-70 mmHg) to prevent cerebral ischemia from brain retraction, brain swelling and vasospasm. Perioperative AVM rupture from hypertension is possible, but rare. However, in case of a coexisting aneurysm, hypertension must be avoided.

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 near 60 mmHg.

Unruptured AVMs

• 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 AVMs

• 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.
• Moderate hyperventilation (PaCO2 30 mmHg) may be useful if concern for elevated ICP

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

AVM rupture

Intraoperative AVM rupture can happen at any time until the malformation is resected. AVM rupture is a true emergency that requires rapid intervention.

If the AVM 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 AVM 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 resection, 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