The effect of nitrous oxide elimination on the rate of decline of exhaled concentration of isoflurane during recovery from general anaesthesia; a comparative study to investigate the presence of reverse second gas effect

Author: 
Prashanth Kumar C, Ramakrishna.Y, Chaitra U and Rammoorthi Rao

Background: The second gas effect can also occur during emergence, with the rapid removal of nitrous oxide increasing the removal of other volatile anesthetics, a phenomenon known as the "reverse second gas effect". The aim of this study was to investigate the presence of this phenomenon. To achieve this study described the rate of decline of exhaled concentrations of isoflurane with and without nitrous oxide.Methods: One hundred patients undergoing surgery under general anesthesia with endotracheal intubation were randomly divided into two groups of fifty each. For Group I, when the gas analyzer monitor indicated an exhaled concentration of 1.2% isoflurane, with nitrous oxide at 66% and oxygen at 33% , the isoflurane was discontinued. For Group NI, when the gas analyzer indicated 1.2% exhaled concentration of isoflurane, with nitrous oxide at 66% and oxygen at 33%, the isoflurane and nitrous oxide both were discontinued, simultaneously. At the same time, the of flow for oxygen was increased to compensate for the loss of nitrous oxide flow. The duration for endtidal concentration of isoflurane to reduce from 1.2% to 0.4% is noted and compared between two groups.Results: Significant difference in measured duration for decline of defined concentration of isoflurane with (36.72sec) and without nitrous oxide (54.04 sec) is noted (p < 0.01). Conclusions: Elimination of nitrous oxide during the recovery enhances elimination of isoflurane. This confirms the presence of reverse second gas effect.

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