The theoretical ideal fresh-gas flow sequence at the start of low-flow anaesthesia.
A spreadsheet model of a circle breathing system and a 70-kg anaesthetised 'standard man' has been used to simulate the first 20 min of low-flow anaesthesia with halothane, enflurane, isoflurane, sevoflurane and desflurane in oxygen. It is shown that, with the fresh-gas flow set initially equal to the total ventilation and the fresh-gas partial pressure to 3 MAC, the end-expired partial pressure can be raised to 1 MAC in 1 min with desflurane and sevoflurane, 1.5 min with isoflurane, 2.5 min with enflurane and 4 min with halothane. Sequences of lower fresh-gas flow and partial pressure settings are given for then maintaining 1 MAC end-expired partial pressure, with a minimum usage of anaesthetic, e.g. 13 ml of liquid desflurane in 20 min (of which only 33% is taken up by the patient) if the minimum acceptable flow is 11.min-1, or 8 ml (with 57% in the patient) if the minimum is 250 ml.min-1.
Mapleson
W W
WW
Department of Anaesthetics and Intensive Care Medicine, University of Wales College of Medicine, Cardiff, UK.
D000328:Adult; D000769:Anesthesia, Inhalation / Q000379:methods*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage* / Q000097:blood; D003198:Computer Simulation; D004334:Drug Administration Schedule; D006801:Humans; D008954:Models, Biological; D010313:Partial Pressure; D012119:Respiration; D012121:Respiration, Artificial
D018685:Anesthetics, Inhalation