Below Knee DVT: Worse Than We Thought

Deep venous thrombosis (DVT) has become the bane of trauma professionals over the past 15+ years. We agonize about how to screen properly, the best ways to prevent, and why it has become such a problem. It’s fairly clear that clot in the veins of the thighs and higher have significant potential to cause major problems, specifically pulmonary embolism (PE).

But what about below the knee DVT? For a long time, we were not as concerned because it was not clear that it actually caused significant complications. I wrote about a study from OHSU last year that addressed this. Now, a recent study published from Scripps Hospital in San Diego confirms the answer to the question.

All trauma patients who were screened for DVT by duplex ultrasound over a 5 ½ year period were enrolled in a retrospective study of the progression and/or complications of this diagnosis. Patients who were at bed rest for 72 hours or who were considered at moderate or higher risk for DVT by American College of Chest Physicians guidelines were screened. Ward patients were screened by duplex weekly, and ICU patients were screened twice a week.

Here are the factoids:

  • Nearly 3,000 of over 11,000 trauma patients were screened (25%)
  • 251 (9%) had DVT or DVT+PE
  • It took an average of 6 days for DVT to appear, and 9 days for PE
  • Two thirds had below knee DVT, one third had above knee disease
  • 4.4% of below knee DVT developed PE
  • Below knee DVT progressed to above the knee in 13% of patients
  • 86% of above knee clot was treated with anticoagulation vs only 24% with below knee DVT
  • 64% of the patients who developed PE were not receiving prophylaxis

Bottom line: Below knee DVT is more significant than we thought, frequently progressing above the knee or throwing off pulmonary emboli. Duplex ultrasound needs to be performed from groin to ankle in at risk patients according to a protocol determined by your hospital. As for what to do when you find below the knee clot, the answer is not yet clear. If the patient has not been receiving chemical prophylaxis, they should at least be started. If they have been receiving prophyaxis, a change to therapeutic dosing is probably warranted. 

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Reference: Below-knee deep vein thrombosis: An opportunity to prevent pulmonary embolism? J Trauma 77(3):459-463, 2014.

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