ABSTRACT
Broadly, breathing systems are divided into those that incorporate a system for carbon dioxide (CO2) absorption and those that do not. Other commonly used classifications are the closed, semi-closed and open systems. In 1954, W. Mapleson, a Cardiff physicist, classified semi-closed breathing systems from A to E, determining their efficiency upon the theoretical fresh gas flow required to prevent the rebreathing of CO2. Mapleson A consists of a T-tube connected to the fresh gas flow outlet, a reservoir bag, reservoir tubing, and an adjustable pressure-limiting valve at the patient end of the circuit. The Mapleson E or Ayres T-piece is only commonly used during the recovery phase of anaesthesia. Utilising the advantages of the Mapleson A, D and E systems, the Humphrey ADE is efficient for both spontaneous and mechanical ventilation. However, the Humphrey ADE is infrequently seen in daily clinical practice.
