50岁男性患者，因肿瘤行右上肺切除，单肺通气后15分钟出现低氧血症。术前检查显示心肺功能良好。术前静息和多巴酚丁胺负荷试验下超声心动图显示左心室功能正常，无任何室壁运动异常。颈动脉多普勒超声检查正常。术前肺功能检查正常，无任何梗阻性疾病（1s用力呼气量3.7 l，1s用力呼气量/肺活量73%）。血电解质、血红蛋白浓度、肾功能正常。无支气管肺部感染病史，吸入空气下动脉血气值为PaO2 83 mmHg，PaCO2 38 mmHg，pH 7.40，HCO3- 25 mM。心电图显示窦性心律，术前血压128/65 mmHg。病人不接受术后硬膜外镇痛。麻醉采用39F左侧双腔管支气管插管，纤维支气管镜确认导管位置正确后，将病人置于侧卧位。采用容量控制通气，FiO2 100% 情况下设置潮气量（VT）7 ml/kg，呼吸频率12次/分钟，呼气末正压（PEEP）5 cmH2O。EtCO2和气道平台压力分别为31 mmHg和19 cmH2O。未观察到内源性iPEEP。单肺通气在呼吸机设置未发生任何变化的情况下启动。15分钟后，患者出现严重低氧血症，脉搏氧分压从94%显著下降到88%。动脉血气显示：pH 7.41，PaO2 52 mmHg（100% FiO2），PaCO2 40 mmHg，HCO3- 24.8 mM和87% SaO2。
A 50-yr-old man undergoing resection of the upper right lung for neoplasia developed hypoxemia 15 min after the start of OLV. Preoperative examination revealed satisfactory cardiopulmonary status. Preoperative rest and dobutamine stress echocardiography revealed normal left ventricular function without any wall motion abnormalities. Doppler ultrasound examination of the carotid arteries was normal. Preoperative pulmonary function tests were normal without any obstructive disease (forced expired volume in 1 s was 3.7 l and forced expired volume in 1 s/vital capacity was 73%). Blood electrolytes, hemoglobin concentration, and renal function were normal. There was no history of bronchopulmonary infection, and arterial blood gas values in room air were PaO2 83 mmHg, PaCO2 38 mmHg, pH 7.40, and HCO3 25 mM. Electrocardiogram showed regular sinus rhythm, and blood pressure on the morning of surgery was 128/65 mmHg. The patient refused epidural anesthesia for management of postoperative pain. Selective bronchial intubation of the left main-stem bronchus was performed with a 39F left-sided double lumen tube (DLT) (Broncho-part; Ru¨sch, Kermen, Germany). The correct position of the tube was immediately confirmed with a fiberoptic bronchoscopy, and the patient was then placed in the lateral position. Volume-controlled ventilation, including a 7 ml/kg tidal volume (VT) of predicted body weight under 100% FIO2, a 12 cycles/min respiratory rate, and a 5 cmH2Opositive end-expiratory pressure (PEEP), was used. End-tidal carbon dioxide and plateau pressure were 31 mmHg and 19 cm H2O, respectively. No intrinsic PEEP was observed. OLV was initiated without any change in ventilator settings. Fifteen minutes later, the patient exhibited profound hypoxemia with a significant decrease in pulse oximetry from 94% to 88%. Arterial blood gas values were pH 7.41, PaO2 52 mmHg (100% FIO2), PaCO2 40 mmHg, HCO3 24.8 mM, and 87% SaO2.