The ability of the lung to tolerate operation or injury without persistent air leaks is primarily dependent on the
a. It is important to recognize that lung involvement in persons with ARDS is heterogeneous and that some portions of the lungs are more adversely affected than others.
b. This involvement can lead to maldistribution of mechanically delivered tidal volume, with some alveoli subjected to more distention than others.
c. Pressures between adjacent alveoli may initially equilibrate, but alveolar pressures eventually increase, creating a pressure gradient between the alveoli and adjacent perivascular sheath. This gradient may result in rupture of the alveoli adjacent to the perivascular sheath, with ensuing passage of air into the perivascular sheath, and proximal dissection into the mediastinum. This condition is often referred to as PIE.
d. In persons with PIE, alveolar air is further decompressed by dissecting along lines of least resistance. These pathways include subcutaneous tissues, where the air produces subcutaneous emphysema, or along tissue planes, resulting in pneumopericardium, pneumoperitoneum, or subpleural air cysts.
e. In the mediastinum, air can track along tissue planes, creating a pneumomediastinum, whereas increased pressures that rupture through the mediastinal pleura produce a pneumothorax.