Wash-in and wash-out of sevoflurane in a test-lung model: A comparison between Aisys and FLOW-i

Petter Jakobsson, Madleine Lindgren, Jan G Jakobsson, Petter Jakobsson, Madleine Lindgren, Jan G Jakobsson

Abstract

Background: Modern anaesthesia workstations are reassuringly tight and are equipped with effective gas monitoring, thus providing good opportunities for low/minimal flow anaesthesia. A prerequisite for effective low flow anaesthesia is the possibility to rapidly increase and decrease gas concentrations in the circle system, thereby controlling the depth of anaesthesia. Methods: We studied the wash-in and wash-out of sevoflurane in the circle system with fixed fresh gas flow and vaporizer setting. We compared two modern anaesthesia work stations, the Aisys (GE, Madison, WI, USA) and FLOW-i (Maquet, Solna, Sweden) in a test lung model. Results: We found fresh-gas flow to have, as expected, a major influence on wash-in, as well as wash-out of sevoflurane. The wash-in time to reach a stable circle 1 MAC (2.1%) decreased from an average of 547 ± 83 seconds with a constant fresh gas flow of 300 ml/min and vaporizer setting of 8%, to a mean of 38 ± 6 seconds at a fresh gas flow of 4 L/min. There were only minor differences between the two works-stations tested; the Aisys was slightly faster at both 300 and 4 L/min flow. Time to further increase circle end-tidal concentration from 1-1.5 MAC showed likewise significant associations to fresh gas and decreased from 330 ± 24 seconds at 300 ml/min. to less than a minute at constant 4 L/min (17 ± 11 seconds), without anaesthetic machine difference. Wash-out was also fresh gas flow dependent and plateaued at 7.5 L/min. Conclusions: Circle system wash-in and wash-out show clear fresh gas dependency and varies somewhat between the Aisys and Flow-i. The circle saturation, reaching 1 MAC end-tidal or increasing from 1-1.5 MAC can be achieved with both work-stations within 1.5 minutes at a constant fresh gas flow of 2 and 4 L/min. Wash-out plateaued at 7.5 L/min.

Keywords: End-tidal concentration; MAC; low-flow anaesthesia; sevoflurane; wash-in.

Conflict of interest statement

Competing interests: No competing interests were disclosed. Jan Jakobsson, have however previously received research grants for previous research activities from Maquet, Abbott, Baxter, MSD, Phitzer, Nycomed, PhaseIn, Grunenthal. He has been lecturing and taken part in advisory board activities for Maquet, Abbott, Baxter, MSD, Phitzer, Nycomed, PhaseIn, Masimo, Grunenthal. He has a paid consult agreement with Linde Healthcare as safety physician.

Figures

Figure 1.
Figure 1.
Wash-in time (minutes) to increase to 1 MAC (sevoflurane 2.1%) for (A) Aysis and (B) FLOW-i anaesthetic work stations.
Figure 2.
Figure 2.
Wash-out time (minutes) for decrease from 1.5 to 0 MAC with sevoflurane at 3.1-0% in (A) Aysis and (B) FLOW-i anaesthetic work stations.

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Source: PubMed

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