Reflection Versus Rebreathing For Administration Of Sevoflurane During Minor Gynecological Surgery

BACKGROUND:Contemporary anesthetic circle systems, when used at low fresh gas flows (FGF) to allow rebreathing of anesthetic, lack the ability for rapid dose titration. The small-scale anesthetic reflection device Anaesthetic Conserving Device (50mL Version; AnaConDa-S) permits administration of volatile anesthetics with high-flow ventilators. We compared washin, washout, and sevoflurane consumption using AnaConDa-S versus a circle system with low and minimal FGF.METHODS:Forty patients undergoing breast surgery were randomized to receive 0.5 minimal alveolar concentration (MAC) sevoflurane with AnaConDa-S (21 patients, reflection group) or with a circle system (low flow: FGF = 0.2 minute ventilation [V '(E)], 9 patients; or minimal flow: 0.1 V '(E), 10 patients). In the reflection group, syringe pump boluses were given for priming and washin; to simulate an open system, the FGF of the anesthesia ventilator was set to 18 L center dot min(-)(1) with the soda lime removed. In the other groups, the FGF was increased for washin (1 V '(E) for 8 minutes) and washout (3 V '(E)). For all patients, tidal volume was 7 mL center dot kg(-)(1) and the respiratory rate adjusted to ensure normoventilation. Analgesia was attained with remifentanil 0.3 mu g center dot kg(-1)center dot min(-1). Sevoflurane consumption was compared between the reflection group and the low- and minimal-flow groups, respectively, using a post hoc test (Fisher Least Significant Difference). To compare washin and washout (half-life), the low- and minimal-flow groups were combined.RESULTS:Sevoflurane consumption was reduced in the reflection group (9.4 +/- 2.0 vs 15.0 +/- 3.5 [low flow, P < .001] vs 11.6 +/- 2.3 mL center dot MAC h(-1) [minimal flow, P = .02]); washin (33 +/- 15 vs 49 +/- 12 seconds, P = .001) and washout (28 +/- 15 vs 55 +/- 19 seconds, P < .001) times were also significantly shorter.CONCLUSIONS:In this clinical setting with short procedures, low anesthetic requirements, and low tidal volumes, AnaConDa-S decreased anesthetic consumption, washin, and washout times compared to a circle system.