HEPARIN-COATED OXYGENATORS SIGNIFICANTLY REDUCE CONTACT SYSTEM ACTIVATION IN AN IN-VITRO CARDIOPULMONARY BYPASS MODEL

Over the past decade our group has shown that the contact system of bl ood is activated in cardiopulmonary bypass (CPB), that heparins enhanc e this activation and that aprotinin reduces both this activation and blood loss in CPB. We have developed an in vitro CPB model to assess t he effects of added components to blood and new components in the arti ficial devices of CPB. In the present study we have compared membrane oxygenators with or without heparin-coated surfaces under identical co nditions in the CPB model. Recalcified ACD blood was circulated in a c losed system for 90 min at 28 degrees C. Blood samples were taken at v arious times during circulation. 4 IU/ml heparin was used with the non -coated oxygenators; no heparin was used in the coated system. Heparin levels were measured in the plasma together with various contact syst em components. Haemolysis, platelet count, platelet factor 4 and alpha (1)-proteinase inhibitor-PMN elastase complexes, were also determined. No heparin was detected during the period of recirculation in samples from the coated oxygenators, showing the excellent adhesive quality o f the heparin coating. In keeping with a significantly greater fall in the platelet count in non-coated us coated oxygenators (mean [+/- SD] final counts of 170 +/- 50 x 10(9)/l and 97 +/- 34.2 x 10(9)/l respec tively after 90 min circulation), platelet factor 4 levels were signif icantly higher (682.9 +/- 187.3% and 95.8 +/- 46.5% of the initial val ue respectively). Also haemolysis (163.0 +/- 33.5% and 125.1 +/- 23.0% ) and degranulation of granulocytes as determined by alpha(1)-proteina se inhibitor-PMN elastase complexes (934.9% +/- 662.5 and 245.1% +/- 6 0.5) were significantly higher with the non-coated oxygenators. Contac t system activation measured by increased kallikrein-like activity was also reduced in the heparin-coated system (141% +/- 27.1 and 108.7% /- 18.4). Factor XII levels (100% to 77% +/- 22.1 and 100% to 88% +/- 16.7) fell much more markedly with the non-coated oxygenators.