Mechanisms of pneumothorax following tracheal intubation.

To investigate the mechanism by which pneumothorax may occur as a complication of tracheal intubation, we submitted four cats to tracheotomy and three to tracheal intubation. To simulate the dissection of air along fascial planes following tracheotomy, we placed catheters in either the pretracheal or subcutaneous plane and applied positive pressure to the catheters. The cats undergoing tracheal intubation were ventilated with excessive positive pressure. Computed tomography was used to document the progression of pneumothorax. High positive pressures during mechanical ventilation led to pneumothorax and pneumomediastinum, and the mechanism was primarily the dissection of air along the perivascular sheaths of the pulmonary arteries, presumably due to rupture of perivascular alveoli. Dissection of air along the pretracheal fascia following tracheotomy produced pneumomediastinum but not pneumothorax. This suggests that pneumothorax occurring clinically is more likely a complication of assisted ventilation than a complication of tracheotomy surgery.