Effect of Recombinant Hirudin, a Specific Inhibitor of Thrombin, on Endotoxin-induced Intravascular Coagulation and Acute Lung Injury in Pigs

We hypothesized that thrombin activation may play a prominent role in endotoxin-induced secondary organ failure, such as acute lung injury. To test this hypothesis, we administered a thrombin-specific inhibitor, recombinant hirudin, in endotoxemic pigs. The pigs were anesthetized, mechanically ventilated, and prepared with Swan-Ganz and extravascular lung water (EVLW) catheters. A total of 18 randomly selected animals received a pretreatment of 1,000 U/kg of hirudin, followed by a continuous infusion over 6 h of 500 U/kg/h given simultaneously with the infusion of 10 µg/kg/h of Salmonella abortus equi endotoxin. Another 18 animals received a continuous infusion over 6 h of endotoxin but did not receive hirudin. All animals were fluid resuscitated with 17 ml/kg/h of saline for the duration of the experiment. Data are expressed as the mean (95% confidence interval). Hirudin reduced the endotoxin-induced consumption of plasma fibrinogen from −110 (−138 to −82) mg/100 ml to −39 (−67 to −12) mg/100 ml (p = 0.0001) and endotoxin-induced increases in the soluble fibrin in plasma from 434 (369 to 499) ng/ml to 236 (171 to 300) ng/ml (p = 0.0002). These data suggest an effective inhibition of the endotoxin-generated thrombin by hirudin. Furthermore, hirudin significantly reduced endotoxin-induced increases in pulmonary vascular resistance from 32 (27 to 37) kdyn × s × cm−5 × kg to 20 (15 to 25) kdyn × s × cm−5 × kg (p = 0.0015) and increases in EVLW from 15.4 (13.2 to 17.6) ml/kg to 12.2 (10.0 to 14.4) ml/kg (p = 0.0299). The administration of hirudin also attenuated the endotoxin-induced loss of protein-rich fluid from the vasculature and reduced the plasma PMN elastase concentration in plasma. These results indicate that the administration of the thrombin-specific inhibitor hirudin can attenuate endotoxin-induced acute lung injury, suggesting an important role of thrombin in endotoxin-induced acute lung injury.