Ultrastructural changes in the lung alveoli after cardiac surgical operations with the use of cardiopulmonary bypass (CPB).

Cardiac surgical procedures with the use of cardiopulmonary bypass (CPB) are commonly complicated by pulmonary dysfunction. The mechanisms of such injury are not well understood. The aim of the present study is to analyze morphologically (mainly ultrastructurally) alveolar injury, which occurred during cardiac surgical operations involving CPB, equipped with a hollow fiber oxygenator. Our study included 20 patients, aged 45-72, who underwent coronary artery bypass grafting. Lung biopsies were taken from the left upper lobe 20 minutes after stopping CPB. Pre-CPB biopsies served as controls. Tissue specimens used for electron microscopy were processed according to standard procedures. Light microscopy revealed only a few alterations in the terminal part of the respiratory tract. Frank edema was seen in some of the alveoli. Extravasated erythrocytes as well as some neutrophils were present in the alveoli and several alveolar capillaries were congested. Ultrastructural observations confirmed the above mentioned changes. Moreover, in many alveoli, extensive injury to air-blood barrier was observed. Type I pneumocytes and endothelial cells appeared swollen or necrotically changed. The cytoplasm of type II pneumocytes was swollen. In many alveoli, pulmonary surfactant could not distribute over the alveolar surface because of edema. Structures of pulmonary surfactant were also seen in alveolar capillaries. The results of this investigation suggest that CPB is associated with some injury to lung tissue. However, this injury seems to be temporary since all examined patients had an uneventful post-operative course.