Fig. 1. Desflurane 2.5% (top ) and 5% (bottom ) in 2 l/min oxygen flowing through dry soda lime; time course of carbon monoxide (CO) concentration (left ordinate, solid line, positive and negative SD bars; 1%= 10,000 ppm) at the absorber outlet and temperature in the center of the absorber canister 3 cm (T1, right ordinate, dashed line, negative SD bars) and 7.5 cm (T2, right ordinate, dotted line, positive SD bars) above the bottom. SD bars plotted only every 5 min. Each point is the mean of three studies. At both concentrations, the temperature increase at the upper sensor lags that at the lower sensor, indicating a moving zone of heat production. The lag is greater at 2.5%. Temperature increase with desflurane is not as fast as with the other compounds. CO production is calculated from the area under the concentration curve. CO production is biphasic. The CO concentration passed its initial maximum when the temperature just started to increase at the upper sensor. CO production shows a second increase with its maximum distinctly separated from the first, when temperature exceeded 40°C at both sensors.