Single lever Humphrey A.D.E. low flow universal anaesthetic breathing system. Part I: Comparison with dual lever A.D.E., Magill and Bain systems in anaesthetized spontaneously breathing adults

The single lever Humphrey A.D.E. anaesthetic system, in both coaxial and parallel (non-coaxial) forms, has recently been introduced. In principle the system offers efficient "universal" function by combining the advantages of Mapleson A, D and E systems. A within-patient comparison of its function in the Mapleson A mode (lever up) in spontaneously-breathing anaesthetized subjects was made to that of the original two lever A.D.E., the Magill (Mapleson A) and the Bain (Mapleson D) systems. The coaxial and parallel single lever A.D.E. systems functioned identically to each other and to the original two lever A.D.E. system, a mean fresh gas flow (FGF) of 51 ml X kg-1 X min-1 causing minimal rebreathing. Under identical conditions, the mean FGF required to just cause rebreathing increased to a mean of 71 ml X kg-1 X min-1 and 150 ml X kg-1 X min-1 with the Magill and the Bain systems respectively. With the single lever system, the switch to its Mapleson E mode for controlled ventilation involves the selection of the only alternative lever position (lever down) without further adjustment. The function and practical advantages in this E mode are presented in Part II.