Another method to prevent venous thrombosis in microsurgery: an in situ venous catheter.

Free-flap failure is in the order of 4 to 10 percent. Heparin is more effective at preventing venous thrombosis than arterial thrombosis. This study was undertaken to investigate the efficacy of delivering heparin at a high dose locally but low dose systemically (heparin infusion via a catheter placed proximal to the venous anastomosis) to prevent venous thrombosis in microsurgery. A model of venous thrombosis was first established by a venous inversion graft in the rat femoral vein (this was performed in seven animals and resulted in 100 percent thrombosis). Saline and heparin were delivered proximal to the inverted vein graft to assess the effect of each in preventing venous thrombosis. Flow/patency distal to the inverted vein graft was assessed by observation under the microscope, the milk test, and rate of flow (flowmeter). Saline infused via a catheter proximal to the venous inversion graft resulted in 100 percent thrombosis in 10 animals. Heparin (100 U/ml at 2 to 3 ml/hour) infused through a catheter for 2 hours proximal to the anastomosis resulted in flow in all 10 animals during the infusion. Blood was also taken before beginning the procedure (control) and after the heparin infusion distal to the anastomosis (local partial thromboplastin time) as well as in the contralateral femoral vein (systemic). The control for all animals that received heparin was <3 minutes. The systemic partial thromboplastin time after heparin infusion was <3 minutes in seven animals, 3.3 minutes in two animals, and >7 minutes in one animal. The local partial thromboplastin time distal to the inverted vein graft was >10 minutes in nine animals and 3.7 minutes in one animal. The study also had a clinical component, in which a catheter was placed in a vein of the free flap, and heparin was infused over 5 days. This technique has been used in 83 consecutive free flaps. In three recent free flaps performed on the limbs, the local partial thromboplastin time (close to the anastomosis) was raised but the systemic time was normal. This technique offers a method in preventing venous thrombosis in microsurgery. It is simple to implement and is not associated with the systemic complications of heparin.