Incidence and prevention of deep venous thrombosis occurring late after general surgery: randomised controlled study of prolonged thromboprophylaxis.
To study the incidence of late deep venous thrombosis (DVT), and to evaluate a regimen of prolonged thromboprophylaxis after general surgery.
                Randomised, controlled, open trial, with blinded evaluation.
                University hospital, Denmark.
                176 consecutive patients undergoing major elective abdominal or non-cardiac thoracic operations, of whom 118 were eligible for evaluation.
                Thromboprophylaxis with a low-molecular-weight heparin, tinzaparin, given for four weeks (n = 58), compared with one week (control group, n = 60).
                Presence of DVT established by bilateral venography four weeks after the operation.
                The incidence of late DVT in the control group was 6/60 (10%, 95% confidence interval (CI) 4% to 21%). In the prophylaxis group it was 3/58 (5.2%, 95% CI 1% to 14%) (p = 0.49).
                Prolonged thromboprophylaxis had no significant effect on the incidence of DVT occurring late after general surgery.
Prolonged thromboprophylaxis with LMWH significantly reduces the risk of VTE compared to thromboprophylaxis during hospital admittance only, without increasing bleeding complications after major abdominal or pelvic surgery.