| Abstract: | Pulmonary insufficiency has become a major problem in the care of patients with extensive cutaneous burns and other forms of trauma. Although a variety of pathological changes have been described in the lungs of such patients, probably the most common underlying lesion is interstitial edema with the development of hyaline membranes. Previous light microscopic investigations have shown that interstitial edema with hyaline membrane development is a nonspecific pulmonary reaction that occurs in many conditions and in response to a variety of stimuli. In this study, postmortem electron microscopic observations on the lungs of six burn patients with the lesion are described. Interstitial edema of the alveolar wall was marked and involved primarily the thick portion of the air-blood membrane. The thin portion of the membrane, where epithelial and endothelial basement membranes are normally in close proximity, did not demonstrate accumulation of edema fluid. There was widespread necrosis of the alveolar epithelium. Cellular debris from necrotic alveolar epithelium and fibrin-like material formed a layer that corresponded to the hyaline membranes observed by light microscopy. Hyaline membranes occurred both with and without edema of the underlying interstitium, seemingly indicating that interstitial edema per se was not solely responsible for the epithelial necrosis and resulting hyaline membranes. Evidence of alveolar epithelial regeneration was also found. The regenerated cells had the appearance of type II alveolar cells (granular pneumocytes), which are thought to be the reserve cells of the alveolus. Changes in the alveolar capillaries were minimal. This was a surprising finding, since changes in the interstitium suggested an altered capillary permeability. However, the possibility that endothelial injury had occurred early in our patients and was repaired by the time of their demise could not be ruled out. Futher ultrastructural studies are needed to describe the sequential development of the lesion and to compare the trauma-related lesion with the interstitial edema-hyaline membrane pattern in other clinical and experimental settings. |
