Unresolved issues in the prevention of venous thromboembolism.

Venous thromboembolism is a potentially fatal complication of surgery. The use of graded pressure stockings in combination with unfractionated heparin (UFH) or a low molecular weight heparin (LMWH) appears to be the safest and most effective method of prevention. With some LMWHs, the risk of venous thromboembolism appears to be lower than that associated with the use of standard UFH. A comparison of heparin given before versus after surgery (with all patients receiving graded pressure stockings) is justified. More information on the benefit-risk ratio of minidose warfarin is also required. The risk of pulmonary embolism (PE) following discharge from hospital after general surgery is relatively low and the extended use of heparin may not be justified. The value of graded pressure stockings and minidose warfarin for the prevention of PE should be determined. The risk of late PE after orthopaedic surgery is unknown and also needs to be determined.