INHIBITION OF PLATELET-FUNCTION BY HEPARIN - AN ETIOLOGIC FACTOR IN POSTBYPASS HEMORRHAGE

The effect of heparin (5 U/ml) on platelet function was examined by he mostatometry in vitro. A wide individual variation of this effect was found in 290 patients who underwent cardiac operations: 8.6% (25) expe rienced a proaggregatory effect, 58.6% (170) experienced a mild to mod erate inhibition of platelet function, and 32.8% (95) experienced a se vere inhibition. No significant difference was found among patient cha racteristics, including antiplatelet medication, in these three subgro ups. In vitro measurements correlated significantly with ex vivo measu rements, that is, from blood taken after heparinization (p < 0.0001; r = 0.97, n = 15). In III patients who underwent cardiac surgical inter vention, a significant correlation (p < 0.0001; 0.4 < r < 0.52) was fo und between preoperative measurements of the degree of inhibition of p latelet function by heparin and the total postoperative blood loss aft er 4, 12, and 18 hours. Similarly, there was a significant difference (p < 0.0001) in the total blood loss at 4, 12, and 18 hours between th e subgroups that showed, in vitro, a mild to moderate inhibition of pl atelet function preoperatively compared with a severe inhibition (713 +/- 43 ml versus 1172 +/- 76 ml at 18 hours). It is concluded that pla telet inhibition as a result of heparin varies among patients and appe ars to be a previously unrecognized etiologic factor in bleeding after cardiopulmonary bypass.