In our December 1, 2009 Patient Safety Tip of the Week “Patient Safety Doesn’t End at Discharge” we began discussion on the potential role of DVT prophylaxis in outpatients. We noted we do it for patients undergoing a few orthopedic procedures and we noted increased attention to the DVT risks in oncology patients.
Now a major population study has really added some urgency to the question of DVT prophylaxis in ambulatory patients. Analysis done on the UK’s Million Women Study (Sweetland et al 2009) looked at the duration and magnitude of the postoperative risk of venous thromboembolism in middle aged women. They found that the incidence of DVT and pulmonary embolism after surgery is substantially increased in the first 12 postoperative weeks, though the risk varies by type of surgery. Risk was highest in the first 6 weeks post-op, peaking during the 3rd week, but remained high for at least 7-12 weeks post-op. The risks for pulmonary embolism paralleled that for DVT. Major orthopedic surgery and cancer surgery had the highest risks, but the increased risks spanned almost all types of surgery. Most interestingly, even same day surgery was associated with a prolonged risk for DVT. That certainly pours water on the argument that immobility is the biggest DVT risk factor.
While this study is an eye opener, don’t run out there and start anticoagulating all your surgical patients for months at a time. We clearly need prospective randomized trials that demonstrate the benefits of prolonged DVT prophylaxis would outweigh the risks. Such studies would have to include a very large sample size, particularly since it is likely that certain subgroups would have greater or lesser risks and benefits.
Another new review (Spyropoulos et al 2009) looks at issues surrounding DVT prophylaxis in medical patients. It notes that data from large clinical trials support LMWH prophylaxis for up to 14 days in medical patients but that most patients are discharged without such prophylaxis. That paper has a good analysis of the duration of prophylaxis issue and also has great discussions on LMWH vs. unfractionated heparin, proper dosing of unfractionated heparin, mechanical DVT prophylaxis, and special populations (eg. obese or those with renal impairment).
Sweetland S, Green J, Liu B, et al. Duration and magnitude of the postoperative risk of venous thromboembolism in middle aged women: prospective cohort study. BMJ 2009; 339: b4583 (Published 3 December 2009)
Spyropoulos AC, Mahan C. Venous Thromboembolism Prophylaxis in the Medical Patient: Controversies and Perspectives. The American Journal of Medicine 2009; 122(12): 1077-1084