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The theoretical ideal fresh‐gas flow sequence at the start of low‐flow anaesthesia
Author(s) -
Mapleson W. W.
Publication year - 1998
Publication title -
anaesthesia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.839
H-Index - 117
eISSN - 1365-2044
pISSN - 0003-2409
DOI - 10.1046/j.1365-2044.1998.00310.x
Subject(s) - medicine , flow (mathematics) , anesthesia , fresh gas flow , ideal (ethics) , sequence (biology) , mechanics , sevoflurane , epistemology , physics , philosophy , biology , genetics
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 1 lmin −1 , or 8 ml (with 57% in the patient) if the minimum is 250 mlmin −1 .