The concentration changes during two low initial fresh gas flow and 2% sevoflurane wash tn semiclosed-circuit anesthesia

Abstract

Objective To investigate the concentration changes of sevoflurane during semiclosedcircuit anesthesia with two low initial fresh gas flow. Methods Forty ASAⅠ-Ⅱ patients undergoing operation were randomly allocated to one of two equal groups （ n = 20）, The vaporize setting of both group were fixed at 2% sevoflurane,group A and group B receive either 2.0 or 1.0 L/rain fresh gas flow. The inspired （F1） ,end-tidal （FA ）, and ratio FA/F1 sevoflurane concentrations were estimated. Results After 120 minutes of sevoflurane anesthesia the inspired and end-tidal sevoflurane concentration were （ 1.47 ± 0.12） % versus （1.69 ±0.09）% （P〈0.01） in the group A and （1.23 ±0.13）% versus（1.46 ±0.11）% （P〈 0.01 ） in the group B. The ratio end-tidal and inspired concentrations/vaporizer setting was 0.73 ± 0.07 and 0.85 ± 0.08 in the group A versus 0.62 ± 0.06 and 0.73 ± 0.07 in the group B. For the ratio inspired and end-tidaL/vaporizer setting there were significant difference between the groups （ P 〈 0.01 ）. The estimated ratio end-tidal/inspired was 0.87 ± 0.08 in the group A versus 0.85 ± 0.09 in the group B （ P 〉 0. 05 ）. Conclusion After 120 minutes of sevotlurane anesthesia at a vaporizer setting of 2% there is a significant difference between tow groups for inspired and end-tidal concentrations, but not for the ratio FA/F1. Key words: Low-flow anesthesia ; Inhalation ; Semiclosed-circuit ; Sevoflurane