Patient Safety Tip of the Week
February 15, 2011 Controversies in VTE Prophylaxis
For many years now we have had a focus on DVT prophylaxis as a patient safety issue. Measures of DVT prophylaxis in surgical cases have been parts of the SCIP project and other core measure systems used by many third party payors. There has even been some movement to expand the role of DVT prophylaxis on the outpatient side (see our December 1, 2009 Patient Safety Tip of the Week “Patient Safety Doesn’t End at Discharge” and our December 2009 What’s New in the Patient Safety World column “More on Ambulatory DVT Prophylaxis”).
Now the pendulum may be starting to swing in the other direction. The DVT risk varies considerably by type of surgery and is also very dependent upon other risk factors that a patient might have. Even the evidence base for use of DVT prophylaxis varies considerably by type of surgery. For many orthopedic surgeries there is a very robust evidence base of high quality studies demonstrating the value of DVT prophylaxis. But the evidence base in other types of surgery may not be as compelling.
Now a new paper by some very respected investigators in the surgical quality improvement field (Qadan 2011) has questioned the current recommendations on venous thrombembolism (VTE) prophylaxis in elective major surgery. The authors collected data on DVT and PE in patients electively undergoing 4 major surgical procedures (colorectal resection, total knee replacement, total hip replacement, and hysterectomy) from a large database from a consortium of academic medical centers for two periods of time (2003-2004 vs. 2007-2008). The study demonstrated a substantial increase in the use of pharmacologic DVT prophylaxis between the two time periods. Yet the rates of DVT and PE were not significantly impacted by this increased use of such prophylaxis. Moreover, the overall rates of DVT and PE were actually quite low and the rates in patients who did not receive pharmacoprophylaxis actually decreased between the two time periods. The authors conclude that this may show that clinical judgment of physicians in choosing which patients need pharmacoprophylaxis is remarkable.
Unfortunately, the study did not have available data on complications of pharmacoprophylaxis (such as hemorrhage, heparin-induced thrombocytopenia, etc.) which might show that the net benefit of prophylaxis may be even lower.
One of the most striking revelations of this paper is that the overall rate of VTE in this elective surgery population is quite low (0.6% to 3.2%). One of the biggest areas of controversy in all prior investigations on VTE has been the means by which DVT is diagnosed. Most randomized controlled trials have used ultrasound techniques to look for evidence of DVT. Many have argued that such techniques artificially increase the incidence and prevalence of DVT by including many cases that will never be clinically relevant. The authors point out industry funding of studies that may overestimate the true VTE rate. They point out that the number needed to treat (NNT) to prevent a single PE in the elective surgical population is about 125 and an even higher NNT would apply to fatal PE. (We, of course, would argue that even one fatal PE is one too many.)
But their point is very well taken. Over the past 5 years we have seen recommendations for aggressive preventive measures in a variety of areas (perioperative beta blockers, tight glucose control, antibiotics for CAP within 4 hours, etc.) all come under fire upon further review. What this study does is put the numbers in perspective and challenge us to take a closer look at the real evidence base for VTE prophylaxis. Most would agree that the decision about VTE prophylaxis should be individualized based upon both patient risk factors and risk factors inherent in the surgical procedure. What we really need is a better understanding of how to more accurately assess the risks based upon analysis of such factors at the individual level.
The current ACCP Evidence-Based Clinical Practice Guidelines on VTE prophylaxis (Geerts 2008) state “based on the results of numerous randomized clinical trials and metaanalyses, the routine use of thromboprophylaxis is recommended following major general surgical procedures”. And those guidelines grade the supporting evidence as Grade 1A, the highest level, for prophylaxis with low-dose unfractionated heparin, low molecular weight heparins (LMWH), or fondaparinux. Yet many of the studies in that evidence base had DVT and PE rates much higher than seen in the Qadan study.
We think the provocative new study by Qadan et al will rekindle the debate about prophylaxis in this patient population. Many of our current pay-for-performance (P4P) systems may be driving the use of pharmacoprophylaxis in all surgical patients. The authors also point to another recent study (Huseynova 2009) that challenged the use of VTE as a marker of quality of care in trauma patients.
So we don’t think we’ve heard the end of this story…
Note also that an interesting recent observation by University of Colorado investigators (Lowry 2011) may also impact the choice of DVT prophylaxis in surgical patients, After seeing anecdotal evidence that patients who had undergone major abdominal surgery did better overall on low-dose heparin infusions than subcutaneous heparin regimens and had no untoward side effects, they studied details of the pharmacoprophylaxis regimens. Most of the patients in the study had cancer and were in the ICU. Most of the patients receiving heparin by the subcutaneous route had hypercoagulable profiles for up to 5 days after surgery but those receiving intravenous heparin had normal profiles. They conclude that perhaps subcuanous heparin prophylaxis may not be the best route for prophylaxis in this patient population but recommend this issue be addressed in a larger randomized controlled trial.
References:
Qadan M, Polk H, Hohmann S, et al. A Reassessment of Needs and Practice Patterns in Pharmacologic Prophylaxis of Venous Thromboembolism Following Elective Major Surgery. Annals of Surgery 2011; 253(2): 215-220, February 2011
Geerts WH, Bergqvist D, Pineo GF, et al. Prevention of Venous Thromboembolism. American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest 2008; 133(6 suppl): 381S-453S
http://chestjournal.chestpubs.org/content/133/6_suppl/381S.full
Huseynova K, Xiong W, Ray JG et al. Venous Thromboembolism as a Marker of Quality of Care in Trauma. J Am Coll Surg 2009; 208: 547-552
http://www.journalacs.org/article/S1072-7515%2809%2900003-9/abstract
Lowry F. Subcutaneous Heparin Not Adequately Absorbed After Abdominal Surgery. Medscape 2011; January 19, 2011
http://www.medscape.com/viewarticle/735994
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