Importance: Pulmonary clots are seen frequently on chest computed tomography performed after trauma, but recent studies suggest that pulmonary thrombosis (PT) and pulmonary embolism (PE) after trauma are independent clinical events. Objective: To assess whether posttraumatic PT represents a distinct clinical entity associated with the nature of the injury, different from the traditional venous thromboembolic paradigm of deep venous thrombosis (DVT) and PE. Design, Setting, and Participants: This prospective, observational, multicenter cohort study was conducted by the Consortium of Leaders in the Study of Traumatic Thromboembolism (CLOTT) study group. The study was conducted at 17 US level I trauma centers during a 2-year period (January 1, 2018, to December 31, 2020). Consecutive patients 18 to 40 years of age admitted for a minimum of 48 hours with at least 1 previously defined trauma-associated venous thromboembolism (VTE) risk factor were followed up until discharge or 30 days. Exposures: Investigational imaging, prophylactic measures used, and treatment of clots. Main Outcomes and Measures: The main outcomes of interest were the presence, timing, location, and treatment of any pulmonary clots, as well as the associated injury-related risk factors. Secondary outcomes included DVT. We regarded pulmonary clots with DVT as PE and those without DVT as de novo PT. Results: A total of 7880 patients (mean [SD] age, 29.1 [6.4] years; 5859 [74.4%] male) were studied, 277 with DVT (3.5%), 40 with PE (0.5%), and 117 with PT (1.5%). Shock on admission was present in only 460 patients (6.2%) who had no DVT, PT, or PE but was documented in 11 (27.5%) of those with PE and 30 (25.6%) in those with PT. Risk factors independently associated with PT but not DVT or PE included shock on admission (systolic blood pressure <90 mm Hg) (odds ratio, 2.74; 95% CI, 1.72-4.39; P <.001) and major chest injury with Abbreviated Injury Score of 3 or higher (odds ratio, 1.72; 95% CI, 1.16-2.56; P =.007). Factors associated with the presence of PT on admission included major chest injury (14 patients [50.0%] with or without major chest injury with an Abbreviated Injury Score >3; P =.04) and major venous injury (23 [82.1%] without major venous injury and 5 [17.9%] with major venous injury; P =.02). No deaths were attributed to PT or PE. Conclusions and Relevance: To our knowledge, this CLOTT study is the largest prospective investigation in the world that focuses on posttraumatic PT. The study suggests that most pulmonary clots are not embolic but rather result from inflammation, endothelial injury, and the hypercoagulable state caused by the injury itself..
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