In order to assess the degree of the pathological changes presenting in the lungs of patients after elective cardiac operations in cardiopulmonary bypass and to determine their prognosis, lung biopsies were taken from the right lower lobe of 36 patients after extracorporeal circulation and studied ultrastructurally. Prepump biopsies from the same presenting anterior portion of the lower lobe of the lung served as controls. Perivascular and interstitial edema featured prominently. Intraalveolar edema and extravasated corpuscular blood elements were observed, too. Damages to the mitochondria and to the lamellar bodies and swelling of the endothelial and alveolar cells were major observations following cardiopulmonary bypass lasting more than 60 minutes. These changes were also prominent in those lungs presenting with severe edema and fibrosis. Many intact type-II pneumocytes presented with enhanced metabolic and secretory activities. Merocrine and apocrine secretions were observed after extracorporeal circulation. The alveoli of the postpump lungs contained numerous detached normal appearing type-II pneumocytes, in contrast to the paucity of such cells in the alveoli of the control biopsies. The prognosis for the patients depends on any one or combination of any of the following factors: the pathological changes present in the lungs prior to the extracorporeal circulation, the duration of the cardiopulmonary bypass, the rate of the elimination of the surfactant and finally the ability of the undamaged type-II pneumocytes to step up the synthesis and secretion of the surface acting agent.
