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

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 CO2 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.

Effects of temperature gradient correction of carbon dioxide absorbent on carbon dioxide absorption.

BACKGROUND: The effects of temperature gradients in CO(2) absorbents on water content and CO(2) absorption are not clear. We constructed a novel temperature gradient correction (TGC) canister, and investigated the effects of temperature gradient correction on the water content and longevity (time to exhaustion) of CO(2) absorbent using a simulated anaesthesia circuit. METHODS: Experiments were divided into two groups according to the type of canister used: the TGC canister (n=6) or the conventional canister (n=6). One kilogram of fresh CO(2) absorbent was placed into the canister. The anaesthetic ventilator was connected to a 3 litre bag and 300 ml min(-1) of CO(2) was introduced. Oxygen (500 ml min(-1)) 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: Before the experiment, the water content of the fresh CO(2) absorbent in the conventional canister and TGC canister was 16.1 (0.9)% and 15.7 (1.1)%, respectively. After the experiment, the water content of CO(2) absorbent near the upper outer rim of the canister increased to 32.4 (0.7)% in the conventional canister, but increased to only 20.6 (1.3)% in the TGC canister (P<0.01). The longevity of CO(2) absorbent in the conventional canister and TGC canister was 434 (9) min and 563 (13) min (P<0.01). CONCLUSIONS: Temperature gradient correction prevented a local excessive increase in water content and improved the longevity of CO(2) absorbent.