Current clinical concepts in perioperative anticoagulation.

Management of patients with significant risks for thromboembolism in the perioperative period requires consideration of both risks of thromboembolism and risks of anticoagulant therapy. Patients who are receiving warfarin therapy because of recent venous thromboembolism, nonvalvular atrial fibrillation, and mechanical heart valves are at increased risk during the interval when the warfarin is discontinued and when the international normalized ratio is at a subtherapeutic level. In patients with an acute venous thromboembolic event within the past month, the use of intravenous heparin appears to be justified both preoperatively and postoperatively. If the venous thromboembolic event was within the past 2 to 3 months, use of intravenous heparin appears justified in the postoperative period. More than 3 months after an acute episode of venous thrombophlebitis, the relatively low risk of recurrence does not appear to justify the risks of complications from intravenous heparin. Patients with increased risks of arterial embolism, specifically those with nonvalvular atrial fibrillation and mechanical heart valves, are generally not at sufficient risk of arterial embolism to justify use of intravenous heparin during the perioperative subtherapeutic international normalized ratio interval when warfarin is withheld. A potential increased risk of recurrent arterial embolism when the preceding event was within a month suggests that elective surgery should be deferred beyond a month whenever possible in such patients. The use of fixed-dose, subcutaneous low molecular weight heparin has been observed to have advantages over use of unfractionated intravenous heparin both in terms of safety and efficiency. Further refinements in management of patients with significant risks of thromboembolism may occur with increased experience with low molecular weight heparin.