The trusted source for
healthcare information and
Nearly 200,000 Americans undergo total hip replacement each year, according to the Health Care Financing Administration in Baltimore. Between 400 and 800 of those patients die in the first three months after surgery because a blood clot forms in a leg vein and later breaks off and lodges in the lungs. Still others develop a painful, swollen leg when a blood clot slows the flow of blood to the heart.
The problem is that both of these complications usually develop long after patients leave the hospital. Now, researchers from the University of California, Davis, report in a recent issue of the New England Journal of Medicine that pneumatic compression, using external devices that massage and compress the legs, dramatically lowers the risk of blood clot formation.
"This is also the first study to show that extended treatment with an anticoagulant drug lowers the risk of developing symptomatic blood clots," says lead author Richard H. White, MD, professor of clinical medicine at the University of California, Davis, School of Medicine and chief of the division of general medicine and director of anticoagulation services at the UC Davis Medical Center.
Past studies, notes White, have also looked at various clot-preventing therapies. These earlier efforts, however, used X-ray images of the veins rather than symptoms to determine the presence of blood clots, which develop in as many as 60% of hip-replacement patients. "Only a small proportion of clots cause symptoms — the rest disappear. So simply detecting clots does not determine which treatments, if any, truly prevent potentially serious symptoms."
Physicians are most concerned about the roughly 3% of hip replacement patients who develop symptomatic clots, he explains.
UC Davis researchers compared total hip replacement patients who actually developed symptoms of blood clots to patients who did not. They analyzed records of California Medicare patients who underwent hip replacement surgery between 1993 and 1996. The medical records of 297 patients who were readmitted for a blood clot were compared to the records of 592 patients who were not readmitted and who presumably did not develop clotting symptoms.
Factors assessed include:
"Our study showed that overweight and obese patients are most at risk for developing blood clots that require hospitalization," White says. Researchers found that overweight patients, or those patients with a BMI of 25 or greater, were 21/2 times as likely to have been hospitalized for clots as patients in the control group.
"We also found that specific groups of patients seem to benefit most from certain treatments." For example, White notes that pneumatic compression was most effective for patients of average weight, but 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." Patients of all weights who continued therapy with the anticoagulant warfarin after they went home were only 60% as likely to have had symptoms as patients in the control group.
Further research may explain why obese patients develop more clots than patients of normal weight, White says. "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."
[See: White RH, Gettner S, Newman JM, et al. Predictors of rehospitalization for symptomatic venous thromboembolism after total hip arthroplasty. N Engl J Med, 2000; 343(24):1758-1764.]