Wash-in kinetics for sevoflurane using a disposable delivery system (AnaConDa) in cardiac surgery patients

The use of volatile anaesthetics has increased in situations where conventional anaesthetic machines are inadequate or unavailable, for example, cardiac surgery and intensive care. The disposable anaesthetic conserving device, AnaConDa, allows vaporization of liquid volatile anaesthetics from a syringe pump and rebreathing of exhaled anaesthetic. Clinical use requires understanding of device-specific anaesthetic agent kinetics, which are not fully known. We compared the wash-in kinetics for sevoflurane administered by a conventional vaporizer in a non-rebreathing system and the AnaConDa and evaluated if a standard anaesthesia gas monitor gave accurate readings while using the AnaConDa.

Cardiac surgery patients were randomized to maintenance of anaesthesia with sevoflurane either via a vaporizer or via the AnaConDa (n=8 in each group). Sevoflurane in arterial blood and airway gas was measured with gas chromatography and standard gas monitoring.

The initial increase in arterial sevoflurane tension was greater with the vaporizer than with the AnaConDa, but the time to reach 80% of maximum sevoflurane tension was close to 8 min in both groups. End-tidal sevoflurane tension mirrored arterial tension in both groups, whereas measured inspired tension was lower than expired and arterial tensions with the use of the AnaConDa.

The wash-in kinetics for sevoflurane delivered by the AnaConDa are similar to a vaporizer. End-tidal sevoflurane tension accurately reflects arterial tension whereas inspired tension may be underestimated using an AnaConDa.