Infratentorial / Posterior Fossa Surgery, Sitting Position Mechanics, and Venous Air Embolism — WACS Viva & Clinical Scenarios (Neuroanaesthesia)

Exam-style infratentorial / posterior fossa surgery, sitting position mechanics, and venous air embolism viva scenarios with examiner probes and model answers…

Scenarios covered

• SCENARIO 1: A 36-year-old woman is positioned in the sitting posture for a retrosigmoid craniectomy to resect a 4 cm vestibular schwannoma. Forty-five minutes into surgical bone resection near the transverse-sigmoid sinus junction, the end-tidal CO₂ abruptly drops from 35 mmHg to 16 mmHg, accompanied by an acute drop in blood pressure from 115/70 mmHg to 68/40 mmHg and a sudden rise in central venous pressure. Formulate your immediate diagnostic confirmation and stepwise crisis management plan.
• SCENARIO 2: A 42-year-old man is scheduled for a suboccipital craniotomy for a cerebellar vermis lesion in the sitting position. During the preoperative assessment, what specific cardiovascular, anatomical, and neurological contraindications to the sitting position must you actively investigate, and what alternative positioning strategies would you discuss with the neurosurgeon?
• SCENARIO 3: A 9-year-old boy with a large fourth-ventricular medulloblastoma presents with signs of severe raised ICP and secondary obstructive hydrocephalus. He is scheduled for prone suboccipital craniotomy. Outline your induction, prone positioning precautions (including eyes, neck, endotracheal tube, and abdominal pressures), and anaesthetic maintenance strategy.
• SCENARIO 4: During microvascular decompression for trigeminal neuralgia in a 54-year-old woman, surgical manipulation near the sensory root of the trigeminal nerve suddenly induces profound sinus bradycardia (heart rate drops from 72 bpm to 26 bpm) and asystolic pauses with unrecordable blood pressure. Deliver your instantaneous anaesthetic response and explain the physiological pathway involved.