title: Expiratory valves and anaesthetic reservoir bags. The implications of scavenging.
abstract: The pressure-volume characteristics of 24 new and old '2-litre' anaesthetic reservoir bags of three different makes were measured. When inflated with gas to a pressure of 50 Pa all the new bags and six used ones contained 1.6 litres and when filled with 2 litres of gas, the pressure within them exceeded 700 Pa. The opening pressures and pressure drops to 30 litres/minute gas flow of scavenging adjustable pressure limiting valves were also investigated. Tests were carried out on 44 valves of four different types, all with their adjusting screws in the fully open position. All the valves had low opening pressures and pressure drops which were both further decreased when the orientation of the valves was changed to the inverted position. A substantial proportion of them remained permanently open. After one year's use both opening pressure and pressure drop tended to rise, the proportion of permanently open valves increased and the discs of some valves were damaged.
authors.forename: S M
authors.initials: SM
authors.lastname: Mostafa
authors.forename: I D
authors.initials: ID
authors.lastname: Hall
mesh_terms: D000769:Anesthesia, Inhalation / Q000295:instrumentation*; D004787:Environmental Pollution / Q000517:prevention & control*; D004868:Equipment Failure; D011312:Pressure; D012015:Reference Standards; D012212:Rheology