How long after surgery does the risk of thromboembolism persist?

Many of the risk factors which occur immediately after major general surgical operations persist for several weeks, and therefore a study was undertaken to assess the incidence of deep vein thrombosis in the 6 week period following surgery. Fifty seven patients who had undergone major surgery were studied, most of whom received deep vein thrombosis prophylaxis in the form of graduated compression stocking and subcutaneous heparin. Only four patients did not receive prophylaxis. Patients were studied for 6 weeks using Doppler ultrasound. 125I-fibrinogen scanning, strain gauge plethysmography and venography. Thirteen of the 51 patients who had not developed a deep vein thrombosis at the time of discharge did so during the 6 week period. It was concluded that the risk factors may persist in many patients and that deep vein thrombosis prophylaxis should be continued for longer than the hospital stay.