Pulmonary microembolism during and after aortic cross-clamping in heparinized and non-heparinized pigs.

The occurrence of pulmonary microembolism after aortic clamping and declamping was investigated in 21 young pigs. The prophylactive effect of heparin was also examined. Eight animals were heparinized, while 13 did not receive heparin. In 15 pigs the plasma concentration of fibrinogen was determined before, during and after clamping of the aorta. External detection of 51Cr-labelled platelets and 125I-labelled fibrinogen was performed. Lung tissue from these animals was homogenized and analysed for radioactivity. Specimens were taken from the lungs of all animals for morphological investigation. A significant decrease in plasma fibrinogen concentration was noted during the aortic clamping in non-heparinized animals. Morphological studies of lung tissue revealed numerous fibrin/platelet thrombi, leukocyte and platelet aggregates, atelectases and bleedings. In homogenized lung tissue, areas with elevated radioactivity were found, indicating fibrin/platelet entrapment. No such changes were seen in pigs pretreated with heparin. It was found that pulmonary microembolism occurs frequently after aortic clamping if heparin is not given at an early stage of the procedure.