In reply.

Abstract

In reply: Dr. Schreiber's letter draws attention to the lack of data regarding the optimal duration of antithrombotic therapy for prevention of venous thromboembolism (VTE) in the high-risk older surgical patient. Although the clinical practice guidelines1 refer to the use of warfarin, this issue applies to alternative therapies as well, including intermittent external pneumatic leg compression and low-dose unfractionated and low-molecular-weight heparins, although comparisons in efficacy between each are also not entirely clear. The risk for VTE increases with age.2, 3 Other risk factors include prolonged immobility or paralysis; prior VTE; cancer; major surgery (particularly operations involving the abdomen, pelvis, and lower extremities); obesity; varicose veins; congestive heart failure; myocardial infarction; stroke; fracture of the pelvis, hip, or leg; indwelling femoral vein catheter; inflammatory bowel disease; nephrotic syndrome; and estrogen use.4 The guideline recommends prophylactic antithrombotic therapy be continued for not less than 3 months or until the patient is ambulatory. Many older surgical patients regain ambulatory status during hospitalization or shortly thereafter. Those remaining bedfast pose the highest risk for VTE and continuation of antithrombotic therapy should be considered for them. As noted, several trials of antithrombotic therapy after hospitalization in patients undergoing hip replacement have found a significant incidence of asymptomatic DVT by venogram at 6 weeks in the placebo groups, with reduction in the incidence of VTE in the treated groups.5-8 One recent study of ardeparin prophylaxis for VTE in total hip and knee replacement patients, however, found that 6 weeks of postoperative therapy did not further reduce VTE incidence beyond that achieved with 4 to 10 days of therapy.9 Reduction in VTE risk must be weighed against the risk of bleeding with antithrombotic treatment. Bleeding risk is most closely associated with the intensity of therapy, which is usually lower for VTE prophylaxis. Additional risk factors include a history of gastrointestinal bleeding, cerebrovascular disease, and renal and hepatic disease.10 To provide some magnitude, the risk of intracranial hemorrhage is 0.3%/year and extracranial hemorrhage is 0.6%/year for warfarin prophylaxis of stroke in atrial fibrillation.11 In summary, it is difficult to extrapolate from currently available data what is the optimal duration of antithrombotic prophylaxis for VTE in non-ambulatory older patients following high-risk surgery; the potential benefit must be weighed against the risk for each patient.