Will we ever have a universal anaesthetic breathing system.

In this issue of the JOURNAL, Humphrey and his colleagues describe a version of the A.D.E. anaesthetic breathing system 1'2 which they feel is optimal for all patients. Humphrey et al . have shown that the "A.D.E. low-flow universal" system functions as a modified D (Mapleson's classification 3) or Bain circuit for controlled ventilation and, with the switch of a single lever, as a modified Mapleson A system (or Lack circuit) for spontaneous respiration. The data presented are largely consistent with previous studies using the "D mode". With controlled ventilation (Part 11) 2 and the D mode (A._D.E.) the arterial PCO2 of ten patients was predictable with a FGF of 70 ml'kg~' min~ and a tidal volume of 10ml'kg -1 with a respiratory rate of 12-15 breaths/minute (i.e., controlled rebreathing). During spontaneous respiration (Part 1) I the authors suggest that rebreathing could be eliminated with FGF rates of only 50 ml'kg~. min~, when the A.D.E. system was used in the "A mode" (A_.D.E.). Several variables determine rebreathing during spontaneous respiration. These considerations are important to the clinician because, as Nunn 4 stated, "it may become almost impossible to determine the composition of the gas inspired." Therefore clinicians must ask two questions: first, does the _A.D.E. system always allow predictable inspired gases, thus safer anaesthesia, at these economically low FGF rates of 50 ml 'kg-l 'min-1; secondly, what potential risks might offset any such advantage? Humphrey et al . ~ studied only healthy (ASA physical status I) patients breathing halothane through an endotracheal tube. The influence of other factors that are known to determine re-