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Volatile anaesthetic blood-gas solubility — FRCA Primary MCQ

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ModeratePharmacologyVolatile anaesthetic blood-gas solubilityFRCA Primary

A volatile agent has blood:gas partition coefficient 2.4 and another has blood:gas coefficient 0.65. Both are delivered at the same inspired partial pressure after induction. Which feature is most likely for the agent with the lower blood solubility?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: A — Lower saturated vapour pressure

A lower blood:gas partition coefficient means less uptake into blood, so alveolar partial pressure rises more quickly and onset is faster. Oil:gas partition relates more closely to potency, not speed of alveolar rise. Hepatic metabolism is a separate property. The teaching point is that blood solubility governs speed of induction and recovery for inhalational agents.

Reference: RCoA Primary FRCA Syllabus 2026; Peck, Hill & Williams Pharmacology for Anaesthesia