Risk factors for deep vein thrombosis and pulmonary embolism after traumatic injury: A competing risks analysis

BACKGROUND Venous thromboembolism, including deep vein thrombosis (DVT) and pulmonary embolism (PE), is typically reported as a composite measure of the quality of trauma center care. Given that recent data suggesting postinjury DVT and PE are distinct clinical processes, a better understanding may result from analyzing them as independent, competing events. Using competing risks analysis, we evaluated our hypothesis that the risk factors and timing of postinjury DVT and PE are different. METHODS We examined all adult trauma patients admitted to our Level I trauma center from July 2006 to December 2011 who received at least one surveillance duplex ultrasound of the lower extremities and who were at high risk or greater for DVT. Outcomes included DVT and PE events, and time-to-event from admission. We used competing risks analysis to evaluate risk factors for DVT while accounting for PE as a competing event, and vice versa. RESULTS Of 2,370 patients, 265 (11.2%) had at least one venous thromboembolism event, 235 DVT only, 19 PE only, 11 DVT and PE. Within 2 days of admission, 38% of DVT cases had occurred compared with 26% of PE. Competing risks modeling of DVT as primary event identified older age, severe injury (Injury Severity Score, 15), mechanical ventilation longer than 4 days, active cancer, history of DVT or PE, major venous repair, male sex, and prophylactic enoxaparin and prophylactic heparin as associated risk factors. Modeling of PE as the primary event showed younger age, nonsevere injury (Injury Severity Score, < 15), central line placement, and prophylactic heparin as relevant factors. CONCLUSION The risk factors for PE and DVT after injury were different, suggesting that they are clinically distinct events that merit independent consideration. Many DVT events occurred early despite prophylaxis, bringing into question the preventability of postinjury DVT. We recommend trauma center quality reporting program measures be revised to account for DVT and PE as unique events. LEVEL OF EVIDENCE Epidemiologic, level III.