Anesthesia and monitoring
hyperventilation
After entering the operating room, all patients received standard ASA monitors. Intraoperative monitoring included electrocardiography (ECG), noninvasive blood pressure, pulse oxygen saturation, end-tidal carbon dioxide (ETCOAll patients were premedicated with 0.05 mg/kg of midazolam intravenously 15 min before anesthesia induction in the operating room. After preoxygenation, anesthesia was induced with 0.3–0.5 µg/kg of sufentanil, 1–3 mg/kg of propofol, and 0.2 mg/kg of cisatracurium. After tracheal intubation, mechanical ventilation was established with a tidal volume of 6–8 ml/kg, a fraction of inhaled oxygen of 60%, a fresh flow of 1 L/min in a semi-closed circuit, and the ventilatory frequency was adjusted between 12–15/min to maintain mild hyperventilation (PaCOIn the desflurane group, anesthesia was maintained with 0.8–1.0 minimum alveolar concentration (MAC) of desflurane combined with 0.05–0.2 µg·kgThe dosage of anesthetics was adjusted to maintain BIS between 40 and 55. The mean arterial pressure (MAP) was maintained at a level of ± 20% compared to baseline. Baseline MAP was defined as the average value of the first three MAP measurements from midazolam administration to induction. If MAP exceeded this range, fluid infusion would be adjusted, and vasopressor or vasodilator would be given accordingly. The intraoperative nasopharyngeal temperature was maintained between 36 °C and 37 °C.