Combining an anaesthetic conserving device with a circle breathing system to minimise isoflurane waste: an in vitro...

To compare isoflurane consumption and efficiency of an anaesthetic conserving device (ACD) and a vaporiser (VAP) in a circle breathing system during artificial ventilation.

In vitro study.

None.

Isoflurane was delivered via VAP or ACD with tidal volumes (V_Ts) of 500 or 4000 mL, creating four setups: VAP500, VAP4000, ACD500 and ACD4000, each repeated four times. The ACD was positioned between an artificial lung and the Y-piece of the breathing circuit. For ACD4000, four ACDs were connected using a 3D-printed connector. Isoflurane delivery followed a predefined decision tree to achieve a concentration of 1.0% in the artificial lung. After reaching steady state, 400 breaths were recorded. Vapour concentrations were measured in the artificial lung (C_lung) and scavenging hose (C_scav). Liquid isoflurane consumption and reflection efficiency (RE) were calculated. Data were analysed using generalised linear mixed models and Mann-Whitney U-tests in SPSS. Results are presented as means (95% confidence intervals).

Liquid isoflurane consumption was lower with ACD500 than with VAP500 [1.2 (1.1-1.3) versus 5.4 mL (5.3-5.6); p = 0.021], and lower with ACD4000 than with VAP4000 [5.2 (4.4-6.0) versus 6.1 mL (5.7-6.4); p = 0.043]. RE was higher with ACD500 than with VAP500 [88.37 (88.17-88.56) versus 46.96% (46.59-47.32); p < 0.001], and higher with ACD4000 than with VAP4000 [93.69 (93.46-93.92) versus 92.61% (92.58-92.65); p < 0.001]. C_scav was lower with ACD500 than with VAP500 [0.0 (0.00-0.00) versus 0.29% (0.29-0.29); p < 0.001], and lower with ACD4000 than with VAP4000 [0.09 (0.07-0.10) versus 0.43% (0.42 - 0.44); p < 0.001].

The ACD reduces isoflurane consumption and C_scav while improving RE at a fresh gas flow of 2 L minute^-1 in circle breathing systems, indicating clinical and environmental benefits.