• J F Coetzee and L J Stewart.
• Department of Anesthesiology, Faculty of Medicine, University of Stellenbosch, Tygerberg, South Africa.
• Br J Anaesth. 2002 Jan 1; 88 (1): 46-55.

MethodsSeven academic centres studied 302 patients, using desflurane, enflurane, halothane, or isoflurane using circle-systems and Dräger Julian anaesthetic machines, with fresh gas flows (V(F)) of 3, 1, and 0.5 litre min(-1). Volatile agent partial pressures in the breathing system were recorded and agent consumptions measured by weighing.ResultsAt these flows, desflurane consumption depended on V(F). In contrast, halothane consumption was not influenced by V(F). Isoflurane and enflurane showed differences in consumption between flows of 0.5 and 3 litre min(-1). Stepwise linear regression suggested that besides V(F), other factors influenced consumption of the more soluble agents (sex, age, weight, height, altitude, and temperature). The partial pressure ratios were independent of V(F) for desflurane (end-tidal to fresh gas=0.8), but the ratios of the more soluble agents varied with V(F) (end-tidal to fresh gas=0.3-0.7).ConclusionsAt V(F) that involves significant re-breathing, consumption of soluble agents depends only partially on V(F). These results can be explained using Mapleson's hydraulic analogue model.

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