A study of waste gas scavenging in operating theatres.

Measurements of atmospheric nitrous oxide concentrations were made in eight hospitals, using 30 anaesthetic machines and locations, during 41 anaesthetic administrations or simulations. All areas were air conditioned, two by laminar flow devices. All anaesthetic machines and ventilators were fitted with commercially available gas collector (scavenger) valves. In all areas except one, venturi suction was used to exhaust gases. Pollution levels during endotracheal anaesthesia did not exceed the recommended 30 ppm. except where leaking anaesthetic machines or nitrous oxide supplies were used. In two instances where paediatric anaesthesia was administered through uncuffed endotracheal tubes nitrous oxide levels were also excessive. Of nine anaesthetics administered through face masks, only in one was the ambient nitrous oxide concentration acceptable. During induction of anaesthesia using nitrous oxide, unacceptable peaks of concentration were encountered. In two air conditioned recovery rooms tested, nitrous oxide concentration was acceptable. The collector valves performed their function satisfactorily, but laminar flow air conditioning was insufficient in itself to maintain acceptably low nitrous oxide concentration without the use of scavenging.