Early Coagulation Events Induce Acute Lung Injury in a Rat Model of Blunt Traumatic Brain Injury

Acute lung injury (ALI) and systemic coagulopathy are serious complications of traumatic brain injury (TBI) that frequently lead to poor clinical outcomes. Although the release of tissue factor (TF), a potent initiator of the extrinsic pathway of coagulation, from the injured brain is thought to play a key role in coagulopathy after TBI, its function in ALI following TBI remains unclear. In this study, we investigated whether the systemic appearance of TF correlated with the ensuing coagulopathy that follows TBI in ALI using an anesthetized rat blunt trauma TBI model. Blood and lung samples were obtained after TBI. Compared with controls, pulmonary edema and increased pulmonary permeability were observed as early as 5 min after TBI without evidence of norepinephrine involvement. Systemic TF increased at 5 min and then diminished 60 min after TBI. Lung injury and alveolar hemorrhaging were also observed as early as 5 min after TBI. A biphasic elevation of TF was observed in the lungs after TBI, and TF-positive microparticles (MPs) were detected in the alveolar spaces. Fibrin(ogen) deposition was also observed in the lungs within 60 min after TBI. Additionally, preadministration of a direct thrombin inhibitor, Refludan, attenuated lung injuries, thus implicating thrombin as a direct participant in ALI after TBI. The results from this study demonstrated that enhanced systemic TF may be an initiator of coagulation activation that contributes to ALI after TBI.