[Application of continuous positive pressure to the uppermost lung in patients ventilated through a single lung]

We have studied the oxygenation process in a series of 20 patients who underwent thoracic surgery and were ventilated through a single lung. There were 19 men and one woman with a mean age (+/- SD) of 63 +/- 10.5 years, a mean height of 166 +/- 37.9 cm and a mean weight of 67 +/- 14.1 kg. Premedication and anesthesia were comparable among all patients. Endotracheal intubation was performed with a double lumen Robersthaw cannula. After anesthetic induction the radial and pulmonary arteries were catheterized to obtain samples for gasometric investigation in arterial and venous mixed blood before and after exclusion of one lung with continuous positive pressure (CPAP). Gasometric analysis was also performed during the immediate postoperative period. All patients were ventilated with 100% oxygen concentration 20 min before blood sampling in order to remove the alveolar nitrogen. During single lung ventilation and during application of CPAP (5 cm H20) to the upright sided lung we observed a 50% increase in arterial p02 (Pa02) (p less than 0.001) without any change in mean alveolar p02 (PA02). There was also a 17% decrease in alveolo-arterial oxygen difference (D[A-a]02) (p less than 0.001) and a 16.6% reduction in the intrapulmonary shunt (Qs/Qt) (p less than 0.001). Improvement of oxygenation was attributed to a beneficial effect of CPAP applied to the upright sided lung while intermittent positive pressure was maintained in the recumbent lung.