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 flowFGF = 0.2 minute ventilation [V′E], 9 patients; or minimal flow0.1 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·min 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·kg and the respiratory rate adjusted to ensure normoventilation. Analgesia was attained with remifentanil 0.3 µg·kg·min. 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·MAC h [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.