Anesthesia and surgery
All the patients were fasted for 6 h and prohibited to drink 2 h before the operation. Routine monitoring was established on all patients including electrocardiogram, peripheral capillary oxygen saturation (SpOBefore induction, all patients were preoxygenated with 100% oxygen for at least 3 min. Induction of anesthesia was started with intravenous sufentanil 0.3 µg/kg, midazolam 0.05 mg/kg, etomidate 0.3 mg/kg, and rocuronium 1.0 mg/kg. After induction, a suitable size Double-Lumen Tube (DLT) was inserted into the left or right bronchus. The position of DLT was confirmed by auscultation and fiberoptic bronchoscope. Mechanical ventilation was used in a pressure-controlled ventilation-volume guaranteed (PCV-VG) mode for protective ventilation in this study. The ventilator parameters were as follow: tidal volume (V