A comparison of desflurane consumption according to fresh gas flow

provided the original work is properly cited. CC The consumption of volatile agents during general anesthesia can be altered by fresh gas flow (FGF), and it is known to be better to maintain an anesthetic effect with a lesser amount of volatile anesthetics because cost considerations, as long as it does not present a safety problem. A previous study reported that the consumption of sevoflurane and isoflurane was decreased in low FGF anesthesia, and the decreased amount was proportional to the FGF rate [1]. We hypothesized that desflurane consumption would proportionally depend on the FGF rate during anesthetic management in surgery. After obtaining Institutional Review Board approval and informed consent, 42 patients, age 20–60 years and scheduled for oro-facial surgery, were randomly allocated to one of two groups: Group F1 received an FGF 1 L/min and Group F3 received an FGF 3 L/min. After arriving in the operating room, all patients were monitored by non-invasive blood pressure, pulse oximeter, electrocardiogram, Entropy, and Surgical Pleth Index (SPI) (GE Healthcare, Helsinki, Finland). Anesthesia induction was performed using propofol and rocuronium. After intubation, administration of 8% desflurane was initiated with an FGF 6 L/min for the first five minutes and then the FGF was switched to 1 or 3 L/min according to the assigned group. Anesthesia was maintained with only desflurane; no adjuvant drugs including nitrous oxide, opioids, intravenous anesthetics, and anti-hypertensive and vasoactive drugs. Blood pressure was maintained within ± 20% from the baseline value, which was obtained before anesthesia induction, and Entropy and SPI were kept below 50. If blood pressure, Entropy, or SPI were out of the maintenance range, the study was paused and the proper treatment was conducted for the patient’s safety. Desflurane consumption was measured using an anesthesia machine (Avance CS2, GE Healthcare, Helsinki, Finland) at 5, 15, 30, and 60 minutes after intubation, when the administration of desflurane was initiated. The analysis was performed using SigmatPlot 12.5 (Systat Software Inc., San Jose, USA). Data were expressed as mean ± SD or median (range; 25–75%). The differences between two groups were analyzed by a t-test or Mann-Whitney rank sum test depending on the results of the normality and equal variance test. Statistical significance was considered at P < 0.05. Five of 42 enrolled patients did not complete the study and were excluded from the statistical results; 18 patients in group F1 and 19 patients in group F3 completed as protocol. There was no statistical difference between the two groups in age, sex, height, weight, the time from intubation to skin incision, the type of surgery, hemodynamic parameters, and anesthetic depth. Desflurane consumption with a FGF 6 L/min for the first five minutes after intubation was 15 (13–15) ml in the F1 group and 14 (12–15) ml in the F3 group, which were not statistically different (P = 0.189). The desflurane consumption for one hour was 54 (49–56) ml in the F1 group and 94 (86–105) ml in the F3 group (P < 0.001, Fig. 1). Although the FGF difference was three-fold (1 vs. 3 L/min) in this study, the desflurane consumption during one hour was less than twofold greater (54 vs. 94 ml). Weiskopt and Eger [2] calculated the desflurane consumption with various FGFs through simulation under the assumption that 1 MAC was kept