Effects of carbon dioxide absorbent cooling and temperature gradient reduction on water condensation in the anaesthesia circuit

Abstract

Background. Large quantities of water condensation occur in the anaesthesia circuit during low-flow anaesthesia. We hypothesized that cooling of the CO2 absorbent would prevent water condensation. Methods. To cool CO2 absorbent efficiently, we constructed a novel temperature gradient reduction (TGR) canister, which was cooled by a blower. Experiments were divided into three groups: the conventional canister group (control group, n=6), the TGR canister without cooling group (TGR group, n=6), and the TGR canister with cooling group (TGR cooling group, n=6). One kilogramme of CO 2 absorbent was placed into the canister. The anaesthetic ventilator was connected to a 3 litre bag and 300 ml min-1 of CO2 was introduced. About 500 ml min-1 of oxygen was used as fresh gas. The anaesthetic ventilator was set at a ventilatory frequency of 12 bpm, and tidal volume was adjusted to 700 ml. Results. The longevity of the CO2 absorbent was 437 (sd 7.8) min in the control group, 564 (13.8) min in the TGR group (P<0.001 vs control), and 501 (5.8) min in the TGR cooling group (P<0.001 vs control, TGR). Total water condensation in the anaesthesia circuit was 215 (9.4) mg min-1 in the control group, 223 (9.7) mg min-1 in the TGR group, and 47.7 (5.7) mg min-1 in the TGR cooling group (P<0.001 vs control, TGR). Conclusions. TGR of CO2 absorbent with cooling is a useful and simple method to reduce water condensation in the anaesthesia circuit in low-flow anaesthesia, with a little increase in the longevity of the CO2 absorbent. © The Board of Management and Trustees of the British Journal of Anaesthesia 2007. All rights reserved.