Research article

Desflurane consumption during automated closed-circuit delivery is higher than when a conventional anesthesia machine is used with a simple vaporizer-O₂-N₂O fresh gas flow sequence

Sofie De Cooman¹ , Nathalie De Mey² , Bram BC Dewulf² , Rik Carette² , Thierry Deloof² , Maurice Sosnowski¹ , Andre M De Wolf³ and Jan FA Hendrickx²

¹Department of Anesthesiology, Institut Jules Bordet, Université Libre de Bruxelles (U.L.B.), Brussels, Belgium

²Department of Anesthesiology, Intensive Care and Pain Therapy, Onze Lieve Vrouw Hospital, Aalst, Belgium

³Department of Anesthesiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA

author email corresponding author email

BMC Anesthesiology 2008, 8:4doi:10.1186/1471-2253-8-4

Published:	17 July 2008

Abstract

Background

The Zeus^® (Dräger, Lübeck, Germany), an automated closed-circuit anesthesia machine, uses high fresh gas flows (FGF) to wash-in the circuit and the lungs, and intermittently flushes the system to remove unwanted N₂. We hypothesized this could increase desflurane consumption to such an extent that agent consumption might become higher than with a conventional anesthesia machine (Anesthesia Delivery Unit [ADU^®], GE, Helsinki, Finland) used with a previously derived desflurane-O₂-N₂O administration schedule that allows early FGF reduction.

Methods

Thirty-four ASA PS I or II patients undergoing plastic, urologic, or gynecologic surgery received desflurane in O₂/N₂O. In the ADU group (n = 24), an initial 3 min high FGF of O₂ and N₂O (2 and 4 L.min^-1, respectively) was used, followed by 0.3 L.min^-1 O₂ + 0.4 L.min^-1 N₂O. The desflurane vaporizer setting (F_D) was 6.5% for the first 15 min, and 5.5% during the next 25 min. In the Zeus group (n = 10), the Zeus^® was used in automated closed circuit anesthesia mode with a selected end-expired (F_A) desflurane target of 4.6%, and O₂/N₂O as the carrier gases with a target inspired O₂% of 30%. Desflurane F_A and consumption during the first 40 min were compared using repeated measures one-way ANOVA.

Results

Age and weight did not differ between the groups (P > 0.05), but patients in the Zeus group were taller (P = 0.04). In the Zeus group, the desflurane F_A was lower during the first 3 min (P < 0.05), identical at 4 min (P > 0.05), and slightly higher after 4 min (P < 0.05). Desflurane consumption was higher in the Zeus group at all times, a difference that persisted after correcting for the small difference in F_A between the two groups.

Conclusion

Agent consumption with an automated closed-circuit anesthesia machine is higher than with a conventional anesthesia machine when the latter is used with a specific vaporizer-FGF sequence. Agent consumption during automated delivery might be further reduced by optimizing the algorithm(s) that manages the initial FGF or by tolerating some N₂ in the circuit to minimize the need for intermittent flushing.