Question: Why is it important that all the valves in a draw-over system are functional?

Answer: The valves ensure that gas flow is in one direction only: gas flows through the vaporiser, to the SIB/bellows, from there to the patient and finally escapes to the atmosphere.

If backward flow occurs, rebreathing may occur which will result in dangerously high concentrations of CO₂ and volatile agent. The patient valve allows lung inflation in the absence of a compressed gas source.