Posterior Fossa Craniotomy (sitting or lateral)
Patient phenotype
Tumors of cerebellum, brainstem, CP angle (vestibular schwannoma); aneurysms; trigeminal neuralgia microvascular decompression. Age 30-70. May have cranial nerve deficits, hydrocephalus.
Procedure
Sub-occipital craniotomy in sitting, prone, or lateral position. Sitting position offers best surgical exposure but highest air-embolism risk. Pre-op echocardiogram to screen for PFO (relative contraindication to sitting).
Anesthetic plan
GETA, position-specific concerns, TIVA + TEE for sitting position. Cranial-nerve monitoring (facial, vestibulocochlear) common. Smooth, neuro-exam-ready emergence.
Setup
- ·Standard ASA + temp + UOP
- ·A-line — pre-induction zeroed at brain level (not heart!) for sitting
- ·Multi-lumen central line tip in atrium (for air aspiration in sitting)
- ·PEEP-tolerant ventilation
- ·Mayfield pin head holder
- ·TEE if sitting (gold standard for VAE detection)
- ·Precordial Doppler (alternative to TEE for VAE)
- ·Sequential compression devices (DVT + venous return in sitting)
Biggest concerns by phase
PFO screening for sitting position
Air entering venous circulation can pass through PFO → arterial → cerebral / coronary catastrophe. ECHO with bubble study before sitting position. PFO presence = use lateral or prone instead.
Cardiovascular tolerance of sitting — preload optimization
Sitting position drops venous return ~30%. Pre-position: hydrate + place SCDs + slow stepwise upright. Vasopressor (NE) often needed during transition. Maintain MAP > 70 for cerebral perfusion. Re-zero A-line at level of brain (not heart) — adds back ~30 mmHg to displayed value.
Venous air embolism — recognize + treat fast
Risk highest with bone work + open dural sinuses above heart level. TEE most sensitive. Signs: ↓ETCO₂ (sudden drop > 10 mmHg), ↓SpO₂, ↓BP, mill-wheel murmur on precordial Doppler. Treatment: tell surgeon flood field, jugular compression, head-down + left lateral, aspirate air from CVC tip, vasopressor + fluid, 100% O₂ (NO N₂O ever in sitting case).
Cranial nerve preservation — anesthetic effect on monitoring
Facial nerve EMG monitoring during CP angle work — NO neuromuscular blockade after intubation dose. Use TIVA + remifentanil to allow nerve responsiveness. Communicate with neuromonitoring tech.
Brainstem manipulation — hemodynamic instability
Surgeon working near brainstem can trigger sudden bradycardia, hypertension, asystole (vagal nuclei). Ask surgeon to pause, treat as needed (atropine, briefly vasoactive support). May be unavoidable for deep tumors.
Smooth emergence + neuro exam in sitting
Position back to supine first. Smooth, no coughing/bucking. Lidocaine pre-extubation. Awake calm patient with neuro exam (cranial nerves) within minutes.
Mock-defense scenarios
Practice answering these out loud. The probes show what an examiner is listening for.
Your patient is in sitting for vestibular schwannoma resection. Mid-tumor dissection, ETCO₂ suddenly drops from 32 to 18, BP 80/40, you hear a 'mill-wheel' murmur on precordial Doppler. What's your immediate action?
What an examiner probes for
- ▹Recognizes venous air embolism
- ▹Communicate with surgeon — flood the field, identify entry point
- ▹Position: head-down + left lateral if feasible
- ▹Aspirate from CVC at atrium
- ▹100% FiO₂, vasopressor, fluid bolus
- ▹Anticipates: confirm with TEE, possibly abort case if persistent
Sources
- Miller's Ch 57
- Cottrell Neuroanesthesia 6e
- SNACC PoFA Guidelines
Anatomy reference
Sourced reference images. 4 matches for "cerebellum brainstem brain".
Browse the full image library →
