The Lack and Bain systems in spontaneous respiration

In conscious subjects breathing spontaneously the performance of the Lack semi-closed system resembled the Magill attachment in that rebreathing was only detected at fresh gas flows of less than resting minute volume. With the Bain semi-closed system rebreathing was detectable at fresh gas flows of the order of 2.5 times the minute volume. The two co-axial circuits behaved similarly for anaesthetised patients. In adults breathing spontaneously the Lack system is efficient and more economical than the Bain.