SEVOFLURANE DEGRADATION BY SODA LIME IN A CIRCLE BREATHING SYSTEM

Sevoflurane is degraded by soda lime to a vinyl either commonly referr ed to as compound A. We measured the concentration of compound A in th e circle breathing system of 31 patients receiving sevoflurane anaesth esia. Inspiratory and expiratory gas samples were analysed using gas c hromatography and flame ionisation detection. The end-tidal sevofluran e concentration and soda lime temperature were recorded. The peak comp ound A concentration ranged between 10 to 32 ppm in the inspiratory li mb and 7 to 26 ppm in the expiratory limb. There was a positive correl ation between the peak compound A concentration and the end-tidal sevo flurane concentration (r(2) = 0.545, p < 0.0001) and the soda lime tem perature (r(2) = 0.301, p = 0.0014). We conclude that the end-tidal co ncentration of sevoflurane and the temperature of the soda lime are im portant variables in determining concentration of compound A in a circ le system.