The Lack, Magill and Bain anaesthetic breathing systems: a direct comparison in spontaneously-breathing anaesthetized adults.

The performances of the Lack (Mapleson A), Magill (Mapleson A) and Bain (Mapleson D) anaesthetic breathing systems were compared in each of 20 anaesthetized adult patients breathing spontaneously with fresh gas flows of 70 ml kg-1 min-1. In every patient the Lack system caused the least rebreathing, as seen by the lowest inspired and end-expired CO2 tensions using capnography. The Magill caused more rebreathing than the Lack though less than the Bain. Comparative fresh gas flows for each system at the point where rebreathing started to occur were examined in 10 further patients. The Lack system required approximately 51 ml kg-1 min-1, the Magill 72 ml kg-1 min-1 while the Bain required 153 ml kg-1 min-1. Of the three systems the Lack is concluded to be the most efficient and economical system for spontaneous respiration in adults, with the additional advantages of convenient access to the exhaust valve, easy scavenging and low expiratory resistance. In addition, it also offers many useful advantages over the circle absorber system.