Clinical comparison of the Bain and Magill anaesthetic systems during spontaneous respiration

Abstract

The Bain and Magill anaesthetic breathing systems were compared for spontaneous breathing during nitrous oxide in oxygen and halothane anaesthesia. A mean fresh gas flow (VF) of 150 ml kg-1 min-1 (SD +/- 30, range 106-250) was required with the Bain system to prevent rebreathing sufficient to cause respiratory stimulation; mean fresh gas flow/expired minute volume (VF/VE) was 1.49 (SD +/- 0.32, range 0.86-2.17). Equivalent figures for the Magill attachment were a mean VF of 82 ml kg-1 min-1 (SD +/- 19, range 43-125), while mean VF/VE was 0.76, (SD +/- 0.19, range 0.38-1.23, P less than 0.001). The results attest the efficiency of the Magill attachment in terms of gas economics, and indicate the very high flows required to avoid respiratory stimulation in some subjects when the Bain system is used.