Breathing systems

Abstract

The classification of apparatus used to deliver inhalational anaesthetic agents to a patient has undergone numerous revisions over the years. The classical terms, open, semi-open, semi-closed and closed, were applicable to the use of ether and are now outdated. Small changes in geometry and gas flow rates can lead to conversion from one type to another, causing confusion. The term breathing system is preferred to the old term breathing circuit, because gases do not flow in a circular path, with the exception of circle systems. A breathing system describes the components and its mode of operation. The terminology can be used generically (e.g. Mapleson A breathing system) or specifically (e.g. Magill breathing system). Breathing systems are customarily divided into three groups: • non-rebreathing systems • systems in which rebreathing is possible • systems using carbon dioxide absorption. By convention, rebreathing in an anaesthetic system refers to inhalation of some or all of the previously exhaled gases, including carbon dioxide and water. This is often considered to be a bad thing, but some rebreathing systems allow for the rebreathing of the alveolar dead space gas, which has already been warmed and humidified and contains no carbon dioxide, hardly an undesirable gas mixture.