The Bain circuit. Prevention of anaesthetic mixture dilution when using mechanical ventilators delivering non-anaesthetic gases.

Experiments using a lung performance analyser demonstrate that if a 1 m length of corrugated 22 mm diameter anaesthetic breathing how (volume 530 ml) is interposed between a lung ventilator delivering air, and the Penlon Bain-type co-axial anaesthetic circuit and valve (volume 660 ml), air-dilution of the respired gas mixture is effectively prevented under conditions likely to be used in clinical practice.