Pulmonary embolism may not originate as deep vein thrombosis in trauma patients, according to a report in the October issue of the Archives of Surgery.
In a study of 46 patients treated over a 3-year period at a single trauma center who developed pulmonary embolism (PE), only 7 (15%) were found to have deep vein thrombosis (DVT) of the pelvic and proximal veins on computed tomographic venography, said Dr. George C. Velmahos of the division of trauma, emergency surgery, and surgical critical care at Massachusetts General Hospital, Boston, and his associates (Arch. Surg. 2009;144:928-32).
“This study is the first to [cast] doubt [on] the traditional belief that PE originates from pelvic and proximal lower extremity veins. We propose that many PEs form primarily in the lungs and that the risk-benefit ratio of vena cava filters should be reconsidered,” they noted.
The prevailing belief is that PE develops when a clot in the leg or pelvic veins breaks apart and part of the clot travels to the pulmonary circulation. Filters for the inferior vena cava were developed to catch those traveling clots before they could lodge in the lungs.
Numerous studies have failed to demonstrate the culprit DVT in patients with PE, but all have relied on ultrasonography or other limited technologies to diagnose DVT. It has been assumed that these techniques are not sensitive enough to detect most DVT, especially when it is located in the pelvis.
Dr. Velmahos and his colleagues reviewed the records of all 247 trauma patients who underwent computed tomographic (CT) pulmonary angiography at their center from 2004 to 2007 and identified 46 found to have PE. There were 18 central PE cases (39%) involving the main or lobar pulmonary arteries and 28 peripheral PE cases (61%) involving the segmental or subsegmental branches.
When the 46 patients were simultaneously examined using CT venography, a much more sensitive detector of DVT than ultrasonography, only 7 were found to have DVT.
Moreover, there were no differences between patients who had DVT and those who did not in age, sex, injury type, length of hospital stay, overall injury severity score, chest injury severity score, use of appropriate anticoagulation therapy, or use of vena cava filters.
The findings demonstrate that PE does not originate from DVT, the authors said, which explains why vena cava filters have not been successful in preventing PE.
In addition, “It can no longer be argued that almost two-thirds of DVT episodes are missed in patients with proven PE solely because the diagnostic tools are inaccurate,” the investigators said.
The researchers’ conclusions are “intriguing,” but the study alone could not establish them as definitive, noted Dr. Raul Coimbra of the division of trauma, surgical critical care, and burns at the University of California San Diego, in an invited critique of the report.
“The lack of a control comparison for CT venography is a significant limitation of the study,” Dr. Coimbra said, and the authors’ attempts to diagnose both DVT and PE concurrently “may lead to erroneous conclusions” if the two are in fact sequential (Arch. Surg. 2009;144:932).
��Perhaps a more consistent screening protocol implemented early after admission would have resulted in more diagnoses of DVTs,” he added. Also, “Velmahos et al. offered no mechanistic explanation for their hypothesis that clots may form de novo in the lungs.”
Neither Dr. Velmahos nor Dr. Coimbra reported any financial conflicts of interest.
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