Predicted and measured oxygen concentrations in the circle system using low fresh gas flows with oxygen supplied by an oxygen concentrator.

An oxygen concentrator based on a zeolitic molecular sieve has been used to supply piped oxygen in a District General Hospital; such oxygen contains 5% argon. If concentrator oxygen is used in the closed circuit, argon accumulates. The present investigation defines the extent and time course of argon accumulation in partially and fully closed breathing systems. A theoretical model is presented which predicts the extent and rate of inert gas accumulation. The predictions have been tested in a volunteer under laboratory conditions and in five anaesthetized patients. It is recommended that concentrator oxygen may be used for low flow anaesthesia of indefinite duration, provided the fresh oxygen flow to the circuit is at least twice the oxygen consumption. If the circuit is totally closed, periodic opening of the circuit is necessary.