A modification of the Bain system for ambient air-oxygen inhalation

In developing countries like Nepal, anaesthetic compressed gases, especially nitrous oxide, are expensive and in short supply and anaesthetic techniques must equally use oxygen and volatile anaesthetics sparingly. We have designed a non-rebreathing anaesthetic system which meets these requirements. An Ambu-E anaesthetic valve and self-inflating Ambu bag connected to a Bain system form a non-rebreathing system which uses ambient air to supplement a mixture of low flow oxygen and halothane. Over 100 patients have been anaesthetised with this system using a balanced anaesthetic technique. The oxygen flow was 2 l.min-1 and the average halothane consumption was 8 ml.h-1. The average inspired oxygen concentration was 34%, and the air:oxygen dilution ratio was 5:1. A graphical analysis of gas flow predicts that the system is almost 100% efficient, in that almost all of the oxygen and halothane will enter the alveoli. Our experience confirms that this is a safe, simple and economical method for inhalation anaesthesia. We recommend it for locations where anaesthetic machines and mechanical ventilators are lacking, and where medical oxygen is in short supply.