Washout of vessels with heparin does not improve patency following severe microarterial trauma: an experimental study

The antithrombotic effect of heparin used as a wash-out solution in small arteries has been evaluated following severe vessel trauma (arteriotomy/intimectomy). Twenty-three central arteries of rabbit ears were prepared and platelets labeled with phosphorus-32 injected intraaortically. The arteries were positioned in double vascular clamps and opened by arteriotomy, and intimectomy was performed. After reestablishing blood flow, arteriotomic bleeding times, platelet accumulation in vivo, patency, and the amounts of intraluminal red thrombotic material were recorded. The rabbits were divided into two groups. In group A (12 vessels) the vessel interior was flushed with 2 ml of saline or Ringer's lactate solution. Group B (11 vessels) was similar except that the vessels were flushed with 2 ml of heparin, 100 IU/ml, in Ringer's lactate solution. In the control group (A) the bleeding time was 5 +/- 2 min, while in group B bleeding was so profuse that extra sutures had to be used in 6 of the vessels. Although significantly fewer platelets accumulated in heparin-treated animals, the patency frequencies and amounts of thrombotic material observed in both groups were similar. The final volume of thrombus formed is thus not always proportional to the degree of platelet accumulation. Washout of small traumatized arteries with heparin is thus not beneficial.