Extended drug therapy and pneumatic compression key to avoiding blood clots after hip replacement surgery

December 12, 2000

Overweight patients at increased risk of developing blood clots

(SACRAMENTO, Calif.) -- A major study of patients who were hospitalized because of life-threatening blood clots after hip replacement surgery reported that pneumatic compression, external devices that massage and compress the legs, can dramatically lower the risk.

"This is also the first study to show that extended treatment with an anticoagulant drug also lowers the risk of developing symptomatic blood clots," says Dr. Richard H. White, whose research team reports its findings in the Dec. 14 issue of the New England Journal of Medicine. Dr. White is a professor of clinical medicine at the University of California, Davis, School of Medicine and Medical Center. He also is chief of the Division of General Medicine and director of the anticoagulation service at UC Davis Medical Center.

About 200,000 Americans each year have a total hip replacement, and most of them are over 65. An estimated 400 to 800 people die in the first three months after surgery because a blood clot forms in a leg vein and then breaks off and lodges in the lungs, a condition known as pulmonary embolism. Others develop a swollen, painful leg when a clot in the leg slows the flow of blood to the heart. These complications, which usually occur after patients leave the hospital, arise more often after hip surgery than after almost any other type of surgery.

Previous studies have looked at various clot-preventing therapies. But these studies have used X-ray images of the veins, rather than symptoms, to determine the presence of a clot, which can develop in 50 to 60 percent of hip-replacement patients. Only a small proportion of clots cause symptoms, and the rest disappear. So simply detecting clots does not determine which treatments, if any, truly prevent symptoms.

"Practicing physicians are most concerned about the 3 percent or so of hip replacement patients who develop symptomatic clots," White explains. Symptoms of deep vein thrombosis include persistent swelling and pain. People who develop pulmonary emboli become short of breath, develop chest pain and may cough up blood. The ultimate goal is to prevent sudden death from pulmonary embolism.

The researchers compared patients who actually developed symptoms to patients who did not. They analyzed the medical records of California Medicare patients who underwent hip replacement surgery between 1993 and 1996. They eventually compared 297 patients who were rehospitalized for a blood clot to 592 who were not rehospitalized and presumably did not develop clotting symptoms. The time limit was 91 days after surgery.

The team assessed a variety of factors, including pneumatic compression, various anticoagulant therapies, and body mass index (BMI), a measure of obesity.

"Our study showed that overweight and obese patients are most at risk for developing blood clots that require hospitalization," White says. "We also found that specific groups of patients seem to benefit most from certain treatments. Pneumatic compression was most effective for patients of average weight, but it did not reduce the risk of serious blood clots in overweight or obese patients. Continuing anticoagulant drug therapy after discharge from the hospital was beneficial to all patients." The researchers found that overweight patients -- those with a BMI of 25 or greater -- were two and one-half times as likely to have been hospitalized for clots as patients in the control group.

Pneumatic compression during the hospital stay appeared to greatly help patients who were not overweight, specifically those whose BMI was below 25. This therapy uses plastic thigh-high cuffs that inflate every few minutes, squeezing blood from ankle to thigh. This mechanical massage is thought to prevent blood from pooling in the veins and clotting. Normal-weight patients treated with pneumatic compression were only 30 percent as likely to have been rehospitalized for symptomatic clotting as patients who did not receive this therapy.

The second beneficial therapy was treatment with warfarin (Coumadin), an anti-clotting drug. Patients of all weights who continued to take warfarin after they went home were only 60 percent as likely to have had symptoms as the controls.

Dr. White sees clot development as one side of a biological teeter-totter. Damage to veins during surgery and lack of normal physical activity tip the teeter-totter toward clotting. Pneumatic compression and warfarin therapy tip it toward clot removal. If a person is overweight, this tends to promote the clotting side.

Further research will hopefully discover why obese patients tend to develop more clots, White declared. "But until we figure out what is going on, overweight patients appear to be the ones who need extended prophylaxis with warfarin or other anticoagulants," he says. He hopes his results will trigger further prospective, randomized studies -- the gold standard for clinical research -- of pneumatic compression. "Large studies of the effectiveness of these devices have been seriously limited because of lack of sufficient funds," he says. "We hope our results will motivate other researchers to carefully study this type of therapy with the goal of making it more effective in obese patients."
-end-
Co-authors on the NEJM study include Kenneth B. Trauner, an assistant professor of orthopaedic surgery at UC Davis, Patrick Romano, an associate professor of internal medicine at UC Davis, and Sharmeen Gettner and Jeffrey M. Newwman, both of California Medical Review, Inc. in San Francisco.

This research was supported by a contract from the Health Care Financing Administration, Department of Health and Human Services.

White RH, Gettner S, Newman JM, Trauner KB, Romano PS. Predictors of rehospitalization for symptomatic venous thromboembolism after total hip arthroplasty. New England Journal of Medicine, 2000; Volume 343.

Copies of all news releases from UC Davis Health System are available on the web at http://news.ucdmc.ucdavis.edu

http://news.ucdmc.ucdavis.edu/bloodclot_study.html

University of California - Davis Health System

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