Heparin-coated oxygenators significantly reduce contact system activation in an in vitro cardiopulmonary bypass model

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Abstract
Over the past decade our group has shown that the contact system of blood is activated in cardiopulmonary bypass (CPB), that heparins enhance this activation and that aprotinin reduces both this activation and blood loss in CPB. We have developed an in vitro CPB model to assess the effects of added components to blood and new components in the artificial devices of CPB. In the present study we have compared membrane oxygenators with or without heparin-coated surfaces under identical conditions in the CPB model. Recalcified ACD blood was circulated in a closed system for 90 min at 28°C. Blood samples were taken at various 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 system components. Haemolysis, platelet count, platelet factor 4 and α1-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 of the heparin coating. In keeping with a significantly greater fall in the platelet count in non-coated vs coated oxygenators (mean [±SD] final counts of 170 ± 50 × 109/l and 97 ± 34.2 × 109/l respectively after 90 min circulation), platelet factor 4 levels were significantly higher (682.9 ± 187.3% and 95.8 ± 46.5% of the initial value respectively). Also haemolysis (163.0 ± 33.5% and 125.1 ± 23.0%) and degranulation of granulocytes as determined by α1-proteinase inhibitor-PMN elastase complexes (934.9% ± 662.5 and 245.1% ± 60.5) were significantly higher with the non-coated oxygenators. Contact 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.

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