The Influence of the Second Gas Effect on the Alveolar Concentration of the Inhalational Anesthetics that have the Different Solubility

Chung, Rack Kyung; Lee, Guie Yong; Kim, Su Mi; Lee, Choon Hi; Cho, Yeon Jin

Abstract

To evaluate the second gas effect and the effect of solubility of volatile anesthetics on the alveolar concentration, the ratio of the end-tidal to the inspired concentration(FET/F1) of enflurane and isoflurane with or without N2O were measured in 40 adult patients in ASA class I or Il. The patients were devided into four groups ; group 1 received 100% O2-1 vol% enflurane, group 2 received 50% O2-50% N2O-1 vol % enflurane, group 3 received 100 % O2-1 vo1% isoflurane and group 4 received 50% 0 50% N2O-1 vo1% isoflurane. The ratio of FET/F1 were measured at 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 30 minute after administration of inhalation anesthetics in each group. The results were as follows. 1) The increase in FET/F1, compared with previous value in each group was significant at 2 minute in group 1 and 2(p<0.05), and at 2 minute and 3 minute in group 3 and 4(p< 0.05), respectively. 2) To compare between group 1 and 2, the significant differance of FET/F1 was noticed during entire observation period and between group 3 and 4, too(p<0.05). This is the result of the second gas effect. 3) The FET/F1 ratio of isoflurane which has lower blood solubility rised more rapidly than the FET/F1 ratio of enflurane. When given without NO, the FET/F1 ratio of group 3 rised significantly more rapidly than the FET/F1 ratio of group 1(p<0.05). But, when given with N2O, changes of the FET/F1 ratio were not significantly different between group 2 and 4. In this study, the alveolar concentration of enflurane and isoflurane rised more rapidly when given with 50% N2O than when given without N2O, it might be the second gas effect by the uptake of NO. And, to the exclusion of the second gas effect, the FET/F1 ratio of less soluble isoflurane rised more rapidly than the more soluble enflurane. But, under the presence of the second gas effect, the difference of the alveolar concentration which depends on the anesthetic solubility between enflurane and isoflurane was not significant.