Gas movement in the nonventilated lung at the onset of single-lung ventilation for video-assisted thoracoscopy

To assess the potential for atmospheric nitrogen to enter the nonventilated lung following the initiation of single-lung ventilation, the nonventilate d lung of 10 patients undergoing video-assisted thoracoscopy was connected to the air in a water-filled spirometer, and gas movement out of and back i nto the lung was measured. Airway pressure from both lungs and pleural pres sure from the nonventilated side were also measured. With each breath of po sitive-pressure ventilation to the ventilated lung prior to the thoracic ca vity being opened to the atmosphere, the pressure transmitted to the opposi te hemithorax generated a mean (range) tidal movement of gas in the nonvent ilated lung of 134 (65-265) mi. In addition, ongoing gas exchange resulted in a progressive influx of gas from the spirometer over the 110-120 s measu rement period of a mean (range) volume of 155 (70-320) mi. This easily prev entable influx of atmospheric nitrogen could, in theory, predispose to arte rial desaturation and to delayed lung collapse after the parietal pleura is opened.