Prevention of posttraumatic pulmonary platelet trapping by portacaval transposition.

Significant soft-tissue trauma induces platelet activation, aggregation, and sequestration in the lungs. This pulmonary trapping is due either to the size of the platelet aggregates or to changes in the pulmonary microvasculature. To evaluate which one of these mechanisms is responsible for the trapping, we performed portacaval transposition in one group of pigs, making the liver the first receiving capillary bed for blood from the trauma sites in the lower extremities. One week after the operation, the platelets were labeled with indium oxine and reinfused, and the operated animals and a group of six control animals were subjected to standardized soft-tissue trauma to the lower extremities. Sequestration of platelets in the lungs and in the liver was registered dynamically before and for 90 minutes after the trauma. Soft-tissue trauma induced platelet sequestration in the liver in the operated group (p less than 0.01) and in the lungs in the control group (p less than 0.01). Trapping was paralleled by a decrease in the number of circulating platelets. This study has indicated that posttraumatic pulmonary platelet trapping is caused by platelet activation at the trauma sites and not by changes in the pulmonary microvasculature.