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Scavenging −0.5 kPa — FRCA Primary MCQ

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ModeratePhysics & Clinical MeasurementScavenging −0.5 kPaFRCA Primary

Regarding scavenging systems for anaesthetic gases the active scavenging system operates at what negative pressure?

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

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Correct answer: D — −0.5 kPa

Active scavenging systems use a pump/fan to draw waste gases away at approximately −0.5 kPa (very low negative pressure). They incorporate a positive pressure relief valve (to prevent barotrauma if outflow is blocked) and a negative pressure relief valve (to prevent application of negative pressure to the patient circuit if flow exceeds extraction). Passive systems rely on gas flow to the exterior without a pump.

Reference: Al-Shaikh Stacey 2019 Essentials of Anaesthetic Equipment