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

OBJECTIVE

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

STUDY

DESIGN

In vitro study.

ANIMALS: None.

METHODS

Isoflurane was delivered via VAP or ACD with tidal volumes (VTs) 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 (Clung) and scavenging hose (Cscav). 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).

RESULTS

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]. Cscav 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].

CONCLUSION AND CLINICAL RELEVANCE: The ACD reduces isoflurane consumption and Cscav while improving RE at a fresh gas flow of 2 L minute-1 in circle breathing systems, indicating clinical and environmental benefits.