Improving the efficiency of the drawover anaesthetic breathing system.

We investigated modifications to the reservoir tube usually used in drawover anaesthetic breathing systems as a method of improving its efficiency and performance. The resulting oxygen concentration was recorded at different oxygen flow rates whilst an artificial lung was being ventilated over a range of minute volumes. Addition of a reservoir bag and valves significantly increased the measured percentage of oxygen at the common gas outlet when compared to a 300-ml reservoir tube. There was no difference in the percentage of oxygen when comparing a reservoir bag and a 600-ml reservoir tube.