Low-flow anaesthesia with desflurane: kinetics during clinical procedures

BACKGROUND AND OBJECTIVE: Low-flow anaesthesia is economical and less polluting. The purpose of this study was to determine the inspired and end-tidal desflurane concentrations during anaesthesia with a vaporizer setting maintained at 5%, during low-flow anaesthesia after 120 min with fresh gas inflows of 1.0 and 2.0 L min-1. METHODS: The study was both prospective and randomized, including 56 patients (28 patients in each group) scheduled for elective surgery of an expected anaesthesia time of at least 120 min. Inspired and end-tidal concentrations of desflurane were measured during low-flow anaesthesia with fresh gas inflows of 1.0 and 2.0 L min-1. The vaporizer setting was fixed at 5% desflurane. RESULTS: The inspired and end-tidal concentrations of desflurane in the 1.0 L min-1 group after 120 min were 4.54% vs. 4.37% (P < 0.001). In the 2.0 L min-1 group, the inspired and end-tidal concentrations of desflurane were 4.76% vs. 4.58% (P < 0.001). The estimated end-tidal/inspired ratios at 120 min of anaesthesia were 0.96 in both groups. At a fresh gas flow of 1.0 L min-1, the end-tidal concentration was 0.87 of the vaporizer setting. Increasing the fresh gas flow to 2.0 L min-1 increased the end-tidal value by 0.05. CONCLUSION: There is a significant difference between the inspired and end-tidal concentrations of desflurane when fresh gas inflows were 1.0 and 2.0 L min-1, but not for the ratio of inspired/end-tidal.