Prophylactic Methods A number of prophylactic methods significantly reduced the incidence of deep venous thrombosis, and a few studies included a large enough patient population to show a reduction in fatal pulmonary emboli (129). The ideal prophylactic method would be effective, free of significant side effects, well accepted by the patient and nursing staff, widely applicable to most patients, and inexpensive.
The use of small doses of subcutaneously administered heparin for the prevention of deep venous thrombosis and pulmonary embolism is the most widely studied of all prophylactic methods.
More than 25 controlled trials demonstrated that heparin given subcutaneously 2 hours preoperatively and every 8 to 12 hours postoperatively is effective in reducing the incidence of deep venous thrombosis. The value of low-dose heparin in preventing fatal pulmonary emboli was established by a randomized, controlled multicenter international trial, which demonstrated a significant reduction in fatal postoperative pulmonary emboli in general surgery patients receiving low-dose heparin every 8 hours postoperatively (129). Trials of low-dose heparin in gynecologic surgery patients showed a significant reduction in postoperative deep venous thrombosis.
Although low-dose heparin is considered to have no measurable effect on coagulation, most large series noted an increase in the bleeding complication rate, especially a higher incidence of wound hematoma (130). Although relatively rare, thrombocytopenia is associated with low-dose heparin use and was found in 6% of patients after gynecologic surgery (130). If patients remain on low-dose heparin for more than 4 days, it is reasonable to check their platelet count to assess the possibility of heparin-induced thrombocytopenia.
Low-molecular-weight heparins (LMWH) are fragments of heparin that vary in size from 4,500 to 6,500 Da. When compared with unfractionated heparin, LMWH have more anti-Xa and less antithrombin activity, leading to less effect on partial thromboplastin time and possibly leading to fewer bleeding complications (131). An increased half-life of 4 hours results in increased bioavailability when compared with unfractionated heparin. The increase in half-life of LMWH allows the convenience of once-a-day dosing.
Randomized controlled trials compared LMWH with unfractionated heparin in patients undergoing gynecologic surgery. In all studies, there was a similar incidence of deep venous thrombosis (DVT). Bleeding complications were similar between the unfractionated heparin and LMWH groups (132). A meta-analysis of general surgery and gynecological surgery patients from 32 trials indicated that daily LMWH administration is as effective as unfractionated heparin in DVT prophylaxis without any difference in hemorrhagic complications (133).
Stasis in the veins of the legs occurs while the patient is undergoing surgery and continues postoperatively for varying lengths of time. Stasis occurring in the capacitance veins of the calf during surgery, plus the hypercoagulable state induced by surgery, are the prime factors contributing to the development of acute postoperative DVT. Prospective studies of the natural history of postoperative DVT showed that the calf veins are the predominant site of thrombi and that most thrombi develop within 24 hours of surgery (134).
Although probably of only modest benefit, reduction of stasis by short preoperative hospital stays and early postoperative ambulation should be encouraged for all patients. Elevation of the foot of the bed, raising the calf above heart level, allows gravity to drain the calf veins and should further reduce stasis.