Changes in arterial oxygenation and pulmonary shunt during thoracotomy with endobronchial anesthesia

Eight-five veterans underwent thoracic operations, mainly for carcinoma of the lung, with the aid of endobronchial anesthesia. Changes in arterial oxygenation (PaO2) and pulmonary shunt (Qs/Qt) were determined sequentially. Mean PaO2 after both lungs were ventilated for 20 minutes, supine, with 100% oxygen was 433 +/- 8 mm Hg. Selective ventilation of one bronchus dropped this value significantly (p less than 0.01) to 247 +/- 13 mm Hg. PaO2 did not change appreciably when the patient was turned to the lateral position; however, following pleurotomy there was a significant (p less than 0.01) decline in mean PaO2 to a nadir of 178 +/- 17 mm Hg at 90 minutes. Transient hypoxemia (PaO2 less than 60 mm Hg) occurred in 11 of 85 patients, most frequently (7/11) during positioning. Preoperative PaO2 PaCO2, forced expiratory volume in 1 second, forced vital capacity, or medical status did not predict hypoxemia. Qs/Qt increased significantly (p less than 0.01) at the onset of atelectasis from 18% +/- 0.9% to 25.4% +/- 0.9% but did not change with turning. The maximal mean Qs/Qt (30.3% +/- 1.1%) occurred immediately after opening the pleura and then decreased significantly (p less than 0.05), despite the fall in PaO2. Blood loss greater than 1,000 cc (n = 10), especially with hypotension, resulted in a significant increase (p less than 0.05) in Qs/Qt and a fall in PaO2. Thus pulmonary vascular adaptation to acute atelectasis has been demonstrated in man, and this, as in animal models, fails with hemorrhage.