Hypoxic Guard O2 N2O Link — FRCA Primary MCQ

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ModeratePhysics & Clinical MeasurementHypoxic Guard O2 N2O LinkFRCA Primary

Regarding the safety features of modern anaesthetic machines the hypoxic guard device prevents:

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Correct answer: E — Delivery of less than 21% oxygen (or 25% depending on manufacturer) by mechanically or pneumatically linking the O2 and N2O flow controls

The hypoxic guard (e.g. Link-25 / Ratio Mixer / S-ORC) mechanically or pneumatically couples the O2 and N2O flowmeter controls so that the minimum O2 concentration delivered is 21-25%. It does NOT protect against hypoxia from other causes (wrong pipeline / cylinder depletion / circuit disconnection / air dilution). Some newer machines use electronic proportioning systems.

Reference: Al-Shaikh Stacey 2019 Essentials of Anaesthetic Equipment