The delivery systems which conduct anaesthetic gases from an anaesthetic machine to the patient are known as breathing systems or circuits. They are designed to allow either spontaneous respiration or intermittent positive pressure ventilation (IPPV) and consist of a reservoir bag, anaesthetic tubing, and (in most cases) a pressure relief valve. A number of mechanical ventilators include a specific breathing system, for example the Manley series. Other ventilators have been designed to operate with existing breathing systems, for example the Penlon Nuffield 200. This article focuses on the breathing systems used with plenum anaesthetic machines (those with a supply of pressurized gas); drawover apparatus will be described in a future article.
Correspondence Email: Quentin.Milner@rdeft.nhs.uk