Inclusion Criteria:  1) NYHA class II or less; 2) expected aortic block time at ≤ 120 min; 3) body mass index (BMI) between 18 and 30 kg/cm2.  Exclusion Criteria:  1) systolic pulmonary blood pressure > 70 mmHg; 2) chronic obstructive pulmonary disease, obstructive sleep apnea syndrome, or simplified airway risk index > 3; 3) Child-Pugh grade B or C liver insufficiency or renal insufficiency (24-h creatinine clearance < 80 mL/min and blood urea nitrogen > 7.5 mmol/L); 4) coagulopathy (aPTT prolongation > 10 seconds versus normal controls, PT prolongation > 3 seconds versus normal controls, and INR > 3.0).