Blood-Gas Partition Coefficient — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

ModeratePharmacology - Inhalational AgentsBlood-Gas Partition CoefficientFRCA Primary

Using conventionally quoted human blood values at 37°C, which inhalational anaesthetic has the lowest blood:gas partition coefficient?

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

Reveal the answer and explanation

Correct answer: D — Desflurane

Desflurane is correct. Its conventionally quoted blood:gas partition coefficient is approximately 0.42, compared with about 0.46 for nitrous oxide, 0.65 for sevoflurane, 1.4 for isoflurane and 2.3 for halothane. The coefficient describes the ratio of anaesthetic dissolved in blood to that present in the gas phase at equilibrium. A lower value indicates lower blood solubility, so alveolar and brain partial pressures change more rapidly during induction and elimination. Nitrous oxide is the closest distractor but its coefficient is slightly higher. Sevoflurane is relatively insoluble but remains more soluble than desflurane; isoflurane and particularly halothane have substantially higher coefficients.

Reference: Electronic Medicines Compendium, Desflurane 100% v/v Inhalation vapour, liquid, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties, updated 7 August 2025. https://www.medicines.org.uk/emc/product/1875/smpc