Maintenance: After endotracheal intubation, the mechanical ventilation is initiated. The tidal volume is set as 6~8 mL/kg, respiratory rate as 10 to 14 times/min and inhalation to exhalation ratio as 1:2. In the surgery, the partial pressure of carbon dioxide in end expiratory gas is kept at the level of 35 - 45 mmHg. And the remifentanil (target concentration of effect compartment is 4 - 8 ng / mL) and propofol (target concentration of plasma is 3 - 5μg / mL) of intravenous target-controlled infusion are given to maintain the anesthesia effect. BIS value is maintained at 40 - 50. Besides, 0.1~0.3μg/kg sufentanil and 0.1~0.2 mg/kg rocuronium are injected intermittently. About 30 minutes before the end of the surgery, a bolus of 0.1~0.3μg/kg sufentanil is administered.