Pulmonary interstitial emphysema in the adult respiratory distress syndrome.

Chest x-rays of 15 patients with the adult respiratory distress syndrome (ARDS) were evaluated retrospectively for the presence of pulmonary interstitial emphysema (PIE). PIE was radiographically detected in 13 (88%) patients, 10 (77%) of whom also had pneumothorax. In five of these, pneumothorax occurred within the first 12 h after interstitial emphysema appeared. Pneumomediastinum was less common and occurred in five (39%) patients. The appearance of PIE and its complications, i.e., pneumothorax and pneumomediastinum, occurred over a wide range of mean airway pressures and positive end-expiratory pressures; there was no direct relationship between barotrauma and mean airway pressure or positive end-expiratory pressure. In 12 of the 13 patients all manifestations of barotrauma occurred at or above a peak airway pressure of 40 cm H2O, indicating a threshold level of peak airway pressure which would place the ARDS patient at high risk for developing pulmonary barotrauma. Time on the respirator at peak airway pressures above 40 cm H2O, clinical severity of ARDS, and associated pulmonary pathology (emphysema, bacterial pneumonia) appear to play a role in developing barotrauma.