The influence of low dose heparin in elective surgery on blood coagulation, fibrinolysis, platelet function, antithrombin III and antiplasmin.

Patients undergoing elective abdominal surgery were randomized into 2 groups, one receiving low dose of heparin (LDH) and one placebo. The code was not opened until all clinical and laboratory tests had been evaluated. LDH had no significant influence on APTT, thrombin time or presence of fibrin monomers except that significantly more patients in the LDH group had prolonged APTT on postoperative day 1, thrombin times greater than 19 sec preoperatively, and fibrin monomers less frequently on postoperative day 5. No significant influence on fibrinogen-related antigens was demonstrable. LDH did not influence the platelet counts or the postoperative increasing aggregability, as illustrated by decreasing threshold concentrations of ADP and adrenalin, increasing frequency of spontaneous platelet aggregation and increase in serotonin release. In contrast the antithrombin III activity against IIa and Xa dropped sigifnicantly more postoperatively in thd LDH group apparently due to increased consumption. The antiplasmin concentration dropped significantly more peroperatively and the fibrinolytic activity increased significantly more in the LDH group immediately postoperatively. The antiplasmin concentrations were significantly in creased later in the postoperative period in both groups, significantly less in the LDH group. These changes induced by LDH favour the inhibition and lysis of thrombus formation.