Anesthesia protocols
Patients were randomly allocated to either minimal fresh gas flow (MF, 0.5 L/min during maintenance) or normal-flow (NF, 2 L/min) general anesthesia. In both groups, participants were first administered with 100% oxygen at a 4 L/min flow rate. Propofol 2–2.5 mg/kg, rocuronium bromide 0.6 mg/kg, and fentanyl 1 mcg/kg IV were used for anesthesia induction. For all general anesthesia procedures, the Drager perseus A500 (Lübeck, Germany) and the Dragersorb were used as anesthesia devices and soda lime, respectively. During induction, all patients were given sevoflurane inhaler anesthesia at a 4 L/min flow rate (FiO