Nitrous cylinder — FRCA Primary MCQ

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HardPhysicsNitrous cylinderFRCA Primary

A nitrous oxide cylinder pressure remains constant until the liquid is exhausted. What is the most important safety consideration?

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

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Correct answer: C — Nitrous oxide liquid-vapour cylinder

Liquid-vapour coexistence keeps pressure near SVP. Heat and moisture exchanger is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Hypoxic guard is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Top of the bobbin gives calibrated flow is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Saturated vapour pressure is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. In Primary FRCA physics and measurement, the safest answer is the one that follows the underlying physical principle and the limitations of the device.

Reference: Davis and Kenny Basic Physics and Measurement in Anaesthesia; RCoA Primary FRCA syllabus