Evaluation of an anaesthetic conserving device in semi-closed rebreathing systems using an artificial lung with isoflurane and sevoflurane: an in vitro pilot study

Objective To evaluate the performance of an anaesthetic conserving device (ACD), in semi-closed, rebreathing systems. Study design In vitro pilot study. Animals None. Methods Firstly, an ACD was positioned between an artificial lung and the Y-piece of a human anaesthesia machine with ventilator, delivering tidal volumes (V T s) of 350, 500, 800 and 1200 mL. Secondly, using a 3D-printed connector, four ACDs were placed in parallel between the artificial lung and the Y-piece of a large animal anaesthesia machine with ventilator, delivering V T s of 4000 and 6000 mL. Each V T , delivered during volume-controlled ventilation, was tested with isoflurane and sevoflurane and with 0 and 10 cmH 2 O of positive end-expiratory pressure (PEEP). Anaesthetic agents were delivered via continuous infusion, aiming for end-tidal concentrations of 1.0% (isoflurane) and 2.0% (sevoflurane). Inspiratory and expiratory vapour concentrations were monitored continuously at the ACD sampling port and at the Y-piece over a 30 minute period. The anaesthetic agent breakthrough (the proportion of exhaled anaesthetic vapour not captured by the ACD) was calculated for each setting and adjusted for the effect of recirculation (recirculation-adjusted breakthrough). Results At low V T s (≤ 500 mL), the ACD adsorbed efficiently, with no (isoflurane) to minimal (≤ 20%) (sevoflurane) loss detected. As V T increased (≥ 800 mL), breakthrough became greater, ranging from 20 – 28% and 40 – 53% for isoflurane and sevoflurane, respectively. The highest recirculation-adjusted breakthrough occurred at 6000 mL with 10 cmH 2 O PEEP for isoflurane (28%) and at 800 mL with 10 cmH 2 O PEEP for sevoflurane (53%). Sevoflurane showed higher breakthrough compared to isoflurane for all the settings. Conclusion and clinical relevance This is the first study to evaluate an ACD in semi-closed, rebreathing systems. The results show that while the ACD effectively captures volatile anaesthetics at low V T s, its breakthrough increased at higher V T s.