A comparison of the early antithrombotic effects between low molecular weight heparin and heparin in small arteries following a severe trauma: an experimental study.

Twenty-seven rabbits divided into 4 groups (2 control groups) received saline, standard heparin (400 IU both as anti-F Xa and activated partial thromboplastin time per kg of body weight), or low molecular weight heparin (lmwh) (Fragmin 560 IU as anti-F Xa and 140 IU as APTT units per kg of body weight). The figures represent the total dose given over 3 hours. The central arteries of the rabbits' ears were prepared and positioned in clamps. Platelets labeled with 32P were injected. Arteriotomy/intimectomy was performed. After reestablishment of blood flow, arteriotomy bleeding times, platelet accumulation, patency, and weight of thrombotic materials were measured. The bleeding time in the Heparin Group was significantly prolonged compared with its control group. But the bleeding times between the LMWH Group and the control group were not significantly different. The patency rates were increased in both the Heparin Group (100%, p < 0.01) and the LMWH Group (73%, p = 0.078) compared with respective control groups (43-50%). The mean weights of thrombotic material in each artery were significantly lower in the Heparin Group and in the LMWH Group than in their control groups. The mean values of radioactivity in all groups increased up to 15 minutes after the vessels were reperfused. There were no statistical differences between the treated groups and control groups. It was concluded that standard heparin is a very powerful inhibitor of thrombosis during the most crucial hours after reperfusion of severely traumatized small arteries, without significant effects on primary platelet adhesion/aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)