Concentration and second gas effects: can the accepted explanation be improved?

British Journal of Anaesthesia
B Korman, W W Mapleson

Abstract

During induction with high inspired concentrations of nitrous oxide, net uptake of gas produces a contraction in volume and a concentrating effect. In turn, this results in concentration and second gas effects. Most explanations of these effects are based on the common "rectangle" diagram devised by Stoelting and Eger and contain several inconsistencies which are explored here in order to produce a more accurate description. It is shown that in the standard diagram gas uptake is incomplete, there is ambiguity over functional residual capacity (FRC), equilibration with blood is inadequately represented and there is no representation of recirculation of anaesthetic. Compensation for loss of volume may be by means of an increased inspired ventilation, decreased expired ventilation or reduction in lung volume. Numerous accounts in the literature (including those based on the standard diagram) focus on the former mechanism at constant FRC. This has produced an unbalanced picture in which it is often implied that extra gas is routinely drawn into the lungs to replace that taken up. Significant compensation by this means cannot occur, for example when a constant volume ventilator is used. In discussing concentration and second gas eff...Continue Reading

Citations

Jun 30, 2000·Canadian Journal of Anaesthesia = Journal Canadien D'anesthésie·K NishikawaF Goto
Sep 29, 2001·British Journal of Anaesthesia·J G Lerou, L H Booij
Apr 6, 2018·Anesthesiology·R Ross Kennedy
Feb 27, 2018·Anesthesiology·Ben KormanPhilip J Peyton
Feb 23, 2008·Anesthesiology·Philip J PeytonBruce R Thompson
Dec 18, 2009·Anaesthesia and Intensive Care·A B Baker

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