There are better DVT prophylaxes than aspirin

Data do not support using aspirin for DVT/PE prevention. AAOS guidelines questioned.

Issue: November 2007

ByFred D. Cushner, MD, FAAOS

I would love to believe that aspirin is a good prophylactic agent. I would also like to believe that there will be peace in the Middle East; that Santa, the Tooth Fairy, Easter Bunny, and Hanukah Harry exist; and that monogamy is a good thing. Unfortunately, I think they all fall under the same category.

Fred D. Cushner

I think the basics are that orthopedists like it simple; that is why aspirin is appealing. I will keep it simple: DVT (deep vein thrombosis) is bad, DVT leads to PE (pulmonary embolism), PE leads to death, and death is usually bad. It is what you try to avoid. Fatal PEs occur, no matter how small we say the numbers are.

I cannot cite one study that shows that the risk of fatal PE is decreased more with a low molecular weight heparin (LMWH) than it is with aspirin. Studies have estimated that they need over 20,000 patients. But just because a study hasn’t been done, doesn’t mean it is not true.

Aspirin revolution

In some ways aspirin is the pot of gold at the end of the rainbow. It is inexpensive. It is easy to administer and it really does not take much thinking to tell the patient to take one aspirin twice a day. But aspirin really has recently had an aspirin revolution. It has almost become a religious experience that aspirin is now going to be accepted for orthopedic use. It has been pushed over the last year since an editorial ran in the Journal of Arthroplasty. But look at the studies involved, they looked at preventing DVT in total knee arthroplasty with aspirin, and at a very high rate. In fact, I would tell you that this rate of DVT is very similar with what you would see with placebo.

There are many things that give you a successful joint replacement. And I don’t think that just not dying is one of them. I don’t want a fatal PE. I don’t want a symptomatic PE or an asymptomatic PE. I don’t want any DVT if I can avoid it. Certainly we can talk about pulmonary hypertension and post-phlebitic syndrome when those above occurrences happen. I think it is clear that aspirin does not prevent DVT.

Paul Lotke, MD, and Jess Lonner, MD, looked at 168 patients and saw no difference in post-thrombotic syndrome, but going through the literature I found at least 30 studies that DVT does increase the instance of post thrombotic syndrome. One author noted an almost two times increase in asymptomatic clots and concluded that when you look at studies DVT is the correct endpoint. John Callaghan, MD, presented a recent study on low- versus high-risk comparing aspirin and warfarin and showed a 0.6% mortality rate in the high-risk group with aspirin and pneumatic compressions.

High-risk patients

I think that it is hard to say who is high risk because of the history of DVT. Warfarin use doesn’t necessarily make a patient high risk. But there are a lot of patients who are high risk that we don’t know about: those with factor five Leiden, protein C and S deficiency, etc. Those are the ones that I worry about the most.

Also, when you look at the DVT data, everybody uses pneumatic compression in their studies, perhaps it is not that aspirin is working alone, but that the aspirin and the pneumatic compression devices that are working. A study by Jeff Westrich, MD, of Hospital for Special Surgery, shows that all sequential compression devices aren’t created equal. So, if you are relying on your DVT prophylaxis from a compression device, certainly if your hospital cut costs to save a couple bucks you may have a device that does not work as well as some of the others.

Also, there is the time requirement. If you critically look at Westrich’s study, DVT was prevented if compression was on 19.6 hours a day. When I try that with my patients, they are off and inflating and deflating in the corner of the room. Often patients are going home earlier, and in Westrich’s study, when compression was only on for 14 hours a day it was much less effective.

Keith Berend, MD, wrote an article “Efficacy of Aspirin” and as a result used LMWH because they own their own hospital and too many of their patients were winding up in a spiral CT. With the new American Academy of Orthopaedic Surgeons (AAOS) guidelines, they have gone back to aspirin (ASA) prophylaxis. Paul Lachiewicz, MD, also done a lot of research and certainly all the results are the same. They all have a fairly high symptomatic PE rate, anywhere from 0.6 to 1.9%.

Is aspirin as effective as warfarin for DVT prophylaxis? I would say that aspirin and warfarin are equally ineffective and you have a similar DVT rate with placebo.

Bleeding is multifactorial. Many of us don’t start the LMWHs at 24 hours and don’t change the dressing until 2 days later. So, when you take that dressing off and it’s a little “oozy” is it because you did a big varus or valgus release? Is it because you did a lateral patella release and blood is coming from the knee or is it from the DVT agent? If you don’t start the agent until 24 hours postop, I would say it is multifactorial and perhaps more time should be spent on a meticulous closure and that way you can limit your bleeding complications.

In closing I would encourage all to look at the AAOS guidelines and you will see that they are guidelines for symptomatic prevention only. No claim for ASA efficacy in DVT prevention is made and the only thing scarier that the guidelines are the length of the disclaimer attached.

For more information:
Fred D. Cushner, MD, can be reached at 210 East 64 St., 4th Floor, New York, NY 10021; 212-870-9740; e-mail: fcush@att.net. He is a consultant for Clearant, Conmed and Zimmer, Inc.
Reference:
Cushner FD. DVT prophylaxis: Aspirin is appropriate — Con. Presented at the 10th Annual Insall Scott Kelly Institute Sports Medicine and Total Hip & Knee Symposium. Held September 14-16, 2007. New York, NY.