Platelets, fibrinogen, and pulmonary haemodynamics in early experimental septic shock

The relationship between platelet trapping, fibrinogen, and pulmonary haemodynamics after iv injection of disintegrated Pseudomonas bacteria into dogs were studied. Platelets were labeled with 51Cr and fibrinogen with 125I. The number of circulating platelets and white cells decreased abruptly within 2 minutes after injection, remained low at 5 minutes, and thereafter slowly increased. At the same time there was a transient increase of 51Cr activity in the lung occurring simultaneously with a decrease in cardiac output and an increase in pulmonary vascular resistance. Pulmonary artery pressure remained constant during the first phase of the experiment and thereafter decreased. There were no signs of 125I-fibrinogen accumulation in the lungs during the 2 hours of the experiment. The results indicate that trapping of platelets and eventually leucocytes in the lungs are closely related to the initial pulmonary haemodynamic changes after injection of disintegrated bacteria, possibly both by release of vasoactive substances and mechanical blocking. This microembolism in the pulmonary microcirculation might be of importance for the development of the shock lung syndrome.