Oxygen Flush Valve — FRCA Final MCQ

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

EasyAnaesthetic Equipment & SafetyOxygen Flush ValveFRCA Final

During anaesthesia on a conventional adult anaesthetic machine with an intact 4 bar pipeline oxygen supply, the emergency oxygen flush is pressed. Which range best represents the oxygen flow delivered to the common gas outlet?

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

Reveal the answer and explanation

Correct answer: B — 35–75 L/min

Explanation lettering: D = shown as A · C = shown as B · E = shown as C · A = shown as D · B = shown as E

C is correct. The emergency oxygen flush takes 100% oxygen downstream of the second-stage regulator, bypassing the flow-control valves and vaporisers, and delivers it directly to the common gas outlet at roughly 35–75 L/min (commonly quoted as about 45 L/min); anaesthetic workstations are specified in this tens-of-litres band. A, B and E are typical rotameter/fresh-gas or facemask oxygen flows and are far too low: the flush is deliberately unregulated to refill a breathing system or reservoir bag almost instantly. D overstates the specification; such flows belong to high-flow nasal oxygen devices, not the flush. Because the flush bypasses vaporisers it dilutes volatile agent (awareness risk), and if pressed during inspiration or with a closed APL valve it can generate dangerously high airway pressures and barotrauma.

Reference: Otteni JC et al. Anesthesia equipment: fresh gas delivery systems. I. Mechanical systems with rotameters and calibrated vaporizers. Ann Fr Anesth Reanim, 1999 (oxygen flush valve output and barotrauma risk). https://pubmed.ncbi.nlm.nih.gov/10615544/