Aspirin: An appropriate prophylaxis for DVT

Given ease of use, effectiveness, availability and patient compliance, aspirin is my choice.

Issue: November 2007

ByJess H. Lonner, MD

While I am a firm believer that aspirin is effective for the majority of our patients as a form of DVT and thromboembolism prophylaxis after total knee and total hip arthroplasty, I am not militant in my approach.

Jess H. Lonner

There are a number of patients in whom I will use warfarin, including those patients who have a history of a pulmonary embolism; proximal deep vein thrombosis (DVT); a recent history of cancer (because they may be hypercoagulable); a genetic risk factor or aspirin intolerance.

We know that the incidence of DVT has been reduced with a variety of different forms of prophylaxes. I will concede that the incidence of DVT is higher with aspirin than it is with some other agents — however there is little clinical significance of an asymptomatic DVT. Unlike the population at large and medical patients where a DVT has often profound significance, the majority of patients with asymptomatic clots after total joint replacement never have problems. Pulmonary embolism (PE) is infrequent, and post thrombotic syndrome doesn’t tend to occur in patients with asymptomatic clots after total joint arthroplasty any more frequently than in patients who had never had a clot. (Lonner et al 2006)

PE incidence low

The incidence of pulmonary embolism is low regardless of what form of prophylaxis is used. It is very clear that the presence of a DVT does not necessarily predispose to a PE. If you look at a variety of different forms of thromboprophylaxis used over a 10- or 15-year period in large studies, the incidence of fatal PE is only about a 0.1% across the board, and that includes aspirin. I think there are plenty of data to support that your total joint patients will be protected with aspirin.

As I see it, the problem with the more aggressive forms of thromboprophylaxis is that they will result in a greater incidence of wound complications. That is what concerns me the most. In my mind the goal of prophylaxis is to reduce the risk of clot propagation, rather than formation, to prevent fatal and symptomatic PE’s, and to use a drug that is relatively low-risk in terms of the incidence of bleeding complications.

There is a balance that we have to strike. We have to find a drug that is effective, but is not going to cause a high rate of hemorrhagic complications that we have seen with some medications.

Quality measure

I am concerned that the Centers for Medicare & Medicaid Services (CMS) have now made venous thromboembolism prophylaxis a core measure of quality care. We are going to be evaluated by what drugs we are using and so are the hospitals. Unfortunately, the CMS guidelines are based on the American College of Chest Physicians (ACCP) recommendations (Geerts et al 2004). Many of us think that these are flawed recommendations in the context of total joint replacement patients. They are promoting drugs and dosages that may be appropriate for at-risk nonsurgical patients, but which may put our surgical patients at undue risk. For instance, CMS advocates for low molecular weight heparin (LMWH), fondaparinux and warfarin, at an International Normalized Ratio (INR) between 2 and 3. Few Orthopaedic surgeons would dose warfarin to a target INR of 2 to 3 because of the very real risk of a considerable bleed at that level. Most of us try to keep the INR less than 2 when using warfarin. It discourages aspirin, but allows for mechanical pumps if epidural anesthesia is utilized.

I think the ACCP is misguided in its recommendations, which have a bias towards a reduction in DVT at the expense of a higher incidence of wound complications, which few of us are willing to accept. In fact, the ACCP recommendations prompted an outcry amongst a number of us who felt that rather than protecting our patients they put them at risk for complications. An editorial in the Journal of Arthroplasty (Callaghan et al 2005) and other grassroots initiatives, prompted the American Academy of Orthopaedic Surgeons (AAOS) to convene a committee charged with developing AAOS-endorsed guidelines for thromboprophylaxis based on an assessment of current scientific and clinical information. These recommendations are more in sync with the balance between efficacy and safety that we, as surgeons, are willing to accept in our clinical practices. This committee condones the use of warfarin, provided the INR is kept below 2 for most standard-risk patients. They also advocate the use of aspirin and pneumatic calf pumps for standard-risk patients, and LMWH for all, particularly the high-risk patients.

The AAOS guidelines accept a higher incidence of asymptomatic DVTs, recognizing that the risk of post-thrombotic syndrome is pretty rare and it favors a lower risk of wound complications given the equivalence of pulmonary emboli across a variety of anticoagulants.

LMWH problems

The problems with LMWH and warfarin are the dreaded bleeding complications that we have all seen and experienced, not to mention the inherent difficulty in dosing warfarin. There have been some recent articles that show some problems with LMWH. This year Burnett el al showed a three-times greater risk of bleeding complications using the ACCP guidelines for LMWH than they observed with warfarin. Patients treated with LMWH had prolonged wound drainage in 9% of cases, and 4.5% required irrigation and debridement or readmission for wound problems. Those statistics are very concerning.

A 2007 study by Patel et al. showed that LMWH had significantly increased wound drainage or hematoma compared to aspirin or Coumadin (warfarin-sodium, Bristol-Meyers Squibb), and that each day of increased wound drainage significantly increased the risk of infection. A 2003 study by Keays et al comparing LMWH and aspirin showed that patients on LMWH had more bleeding complications and a more difficult time gaining motion than those on aspirin.

Our experience

In 2006 Lotke and I looked at our experience with 3,500 primary knees, in nonselected patients from both of our practices. We used Ecotrin (aspirin, GlaxoSmithKline) 325 mg twice a day; we didn’t routinely use foot pumps. We had 100% follow up at 6 weeks, which is really a critical period of time. We found that the incidence of fatal PE was 0.06%, nonfatal PEs 0.26%, and symptomatic DVTs 0.2%.

While aspirin is typically seen as less effective than other agents in preventing DVT, the rate of fatal PE is similar and it has a lower bleeding risk than those other alternatives. It is easy, it is effective and it is inexpensive. Patients prefer it; we don’t have to monitor them or their blood levels. The risk profile is also attractive; these patients are less likely to bleed and the AAOS now supports it use, as do the data.

When you choose a method of thromboembolism prophylaxis, ultimately you have to make a decision about whether you want to reduce the risk of DVT at the expense of increased bleeding complications (which is typical with most contemporary options) or whether you are willing to accept a higher incidence of DVTs but reduce equivalently the incidence of pulmonary emboli and fatal pulmonary emboli, and have a substantially reduced tendency for wound complications (which is what aspirin provides).

For more information:
Jess H. Lonner, MD, director of knee replacement surgery, can be reached at Pennsylvania Hospital, 800 Spruce St., Philadelphia, PA 19107; 215-829-2461; e-mail: jlonner@mail.med.upenn.edu. He is a consultant for Zimmer.
References:
Burnett RS, Clohisy JC, Wright RW, et al. Failure of the American College of Chest Physicians-1A protocol for Lovenox in clinical outcomes for thromboembolic prophylaxis. J Arthroplasty. 2007;22:317-324.
Callaghan JJ, Dorr LD, Engh GA, et al. Prophylaxis for thromboembolic disease. Recommendations from the American College of Chest Physicians — are they appropriate for orthopaedic surgery? J Arthroplasty. 2005;20:273-274.
Geerts WH, Pineo GF, Heit JA, et al. Prevention of venous thromboembolism: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Chest. 2004;126(3 Suppl):338S-400S.
Keays AC, Mason M, Keays SL, Newcombe PA. The effect of anticoagulation on the restoration of range of motion after total knee arthroplasty: Enoxaparin versus aspirin. J Arthroplasty. 2003;18:180-185.
Lonner JH. DVT prophylaxis: Aspirin is appropriate. Presented at the 10th Annual Insall Scott Kelly Institute Sports Medicine and Total Knee & Hip Symposium. Sept. 14-16, 2007. New York.
Lonner JH, Frank J, Lotke PA. Post-thrombotic syndrome after asymptomatic deep venous thrombosis following total knee and hip arthroplasty. Am J Orthop. 2006;35:469-472.
Patel VP, Walsh M, Sehgal B, et al. Factors associated with prolonged wound drainage after primary total hip and knee arthroplasty. J Bone Joint Surg Am. 2007;89A:33-38.
Lotke PA, Lonner JH. The benefit of aspirin chemoprophylaxis for thromboembolism after total knee arthroplasty. Clin Orthop Relat Res. 2006;452:175-180.
For a list of the American Academy of Orthopaedic Surgeons guidelines go to www.aaos.org/Research/guidelines/PE_guideline.pdf.