General anesthesia
Subsequently, propofol (2 ~ 2.5 mg/kg) and cisatracurium besylate (0.15 mg/kg) were used for the induction of anesthesia before a laryngeal mask was applied. The mechanical ventilation settings were 6–8 ml/kg tidal volume and 10–12 times/min respiratory rate. Anesthesia was maintained with sevoflurane inhalation (≤ 1 MAC) and target-controlled infusion of propofol (30–50 µg/kg/min). The amount of anesthetic was appropriately adjusted to maintain an intraoperative end-tidal carbon dioxide partial pressure (P