The Rate Of Decline Of Exhaled Concentrations Of Isoflurane With And Without Nitrous Oxide

The purpose of this study was to investigate the presence of a "reverse second gas effect". To achieve this purpose the study investigated the rate of decline of exhaled concentrations of isoflurane with and without nitrous oxide. A total of 60 subjects were studied. The effects of age, weight, gender, and ASA status were also investigated. The study identified that there was no difference in the rate of decline of exhaled concentrations of isoflurane with and without nitrous oxide regardless of age or ASA status. In this sample the variables of gender and weight were found to affect the rate of decline. It has been shown in prior studies that nitrous oxide facilitates the onset of anesthesia by accelerating the rise of inspired concentrations of an anesthetic gas.(1) Nitrous oxide has been found to also facilitate the emergence from anesthesia by increasing the rate of decline of exhaled concentrations of an anesthetic gas.(4) Since isoflurane is one of the most commonly used anesthetic gases, it was examined for the influence of nitrous oxide and the "reverse second gas effect". Data analyses identified no significant difference in the elimination of isoflurane whether nitrous oxide was used or not used. Only one weight group, 90 to 125 kg, had a significant difference in elimination duration. Anesthetists should use the results of this study to guide the delivery of anesthesia. Nitrous oxide should not be expected to speed the rate of emergence from general anesthesia.