Brain Relaxation Craniotomy — FRCA Final MCQ

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ModerateNeuroanaesthesiaBrain Relaxation CraniotomyFRCA Final

A 40-year-old man (ASA I, 80 kg) is undergoing a craniotomy for excision of a frontal meningioma. The neurosurgeon requests brain relaxation. Which of the following interventions is most effective at reducing brain bulk intraoperatively?

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Correct answer: E — Hyperventilation to PaCO2 3.5-4.0 kPa AND mannitol 0.5 g/kg

Brain relaxation during craniotomy is achieved through a combination of: (1) mild hyperventilation (PaCO2 3.5-4.0 kPa) – reduces CBF by cerebral vasoconstriction (each 1 kPa reduction in PaCO2 reduces CBF by ~25%), (2) osmotic therapy (mannitol 0.25-0.5 g/kg or hypertonic saline), (3) CSF drainage (via lumbar drain or ventricular puncture), (4) 15-30° head-up positioning (improves venous drainage), (5) avoidance of venous obstruction (no neck rotation/compression). Excessive hyperventilation (<3.5 kPa) risks cerebral ischaemia. Deepening volatile anaesthesia INCREASES CBF (cerebral vasodilation) and worsens brain swelling.

Reference: NACCS – 2023 – Neuroanaesthesia guidelines; RCOA – 2023 – Neuroanaesthesia module