Robert M. Hardaway

Prevention of adult respiratory distress syndrome with plasminogen activator in pigs

Death from traumatic shock has been associated with loss of blood externally or internally. However, many patients die after trauma, even though blood volume restoration is adequate. Death is often due to pulmonary failure (adult respiratory distress syndrome [ARDS]). Death and ARDS have been associated with disseminated intravascular coagulation (DIC) and microclots in the lungs. Dissolution of the microclots after trauma can be achieved by activation of endogenous plasmin. Nine pigs were anesthetized for 48 h. Trauma was administered by 60 standard blows to each thigh resulting in a bruise of muscle but no skin, bone, or major vessel injury. Nutrition and respiration were maintained at normal levels. All nine pigs died with severe lung pathology and low PaO2. Ten other traumatized pigs were treated with a plasminogen activator iv 4 h after trauma. Five of these were treated with tissue plasminogen activator (tPA) and five with urokinase. All treated pigs survived 48 h and maintained a normal PaO2. Autopsy showed minimal lung pathology.

Trauma, Sepsis, and Disseminated Intravascular Coagulation

Disseminated intravascular coagulation (DIC) was first observed clinically in a case of sepsis following severe trauma. It was postulated that the observed clotting defect and bleeding were due to the using up of clotting factors in an episode of intravascular clotting. It was also postulated that the multiple organ failure observed was due to obstruction of the microcirculation of the organs by microclots. Evidence for this process was worked out in many animal studies. It was then postulated that if these microclots could be lysed before organ necrosis was produced, organ failure could be prevented. This prevention was shown to be possible in animals. It was then tried in humans using plasminogen activators, and the approach was found to be effective. Using a low dose of plasminogen activator over a 24-hour period caused no changes in the coagulation profile or bleeding.

A new treatment for traumatic shock and ARDS

Trauma causes more years of lost life than any other cause of death. Traumatic shock and sepsis are the most common late causes of death following trauma. Traumatic shock and sepsis cause multiple organ failure. The most common organ to fail is the lung, which develops Adult Respiratory Distress Syndrome (ARDS). ARDS can be caused by Disseminated Intravascular Coagulation (DIC) with microscopic clots in the lungs. Trauma causes hemolysis and the red cell stroma may initiate DIC. Plasminogen activators, which causes lysis of blood clot, can lyse pulmonary microthrombi and prevent the onset of ARDS even when given several hours after the trauma.

Organ Failure and Disseminated Intravascular Coagulation

Disseminated intravascular coagulation (DIC) involves the formation of fibrin from fibrinogen. This results in two important effects: (a) The onset of a clotting defect due primarily to the using up of clotting factors faster than they can be manufactured. (b) The precipitation of fibrin fibers primarily on the most available surface, that of red cells (Fig. 1). This results in the formation of red cell conglomerates, which occlude the microcirculation. It is this second effect which is our present concern.