CELL ACTIVATION AND THROMBIN GENERATION IN HEPARIN BONDED CARDIOPULMONARY BYPASS CIRCUITS USING A NOVEL IN-VITRO MODEL

Objective: It is generally agreed that when the blood contact surfaces of a cardiopulmonary bypass circuit are treated with a layer of hepar in molecules the activation of the humoral pathways is attenuated. How ever, there is still debate as to whether heparin-bonded circuits redu ce thrombin generation. This study aims to examine the effects of immo bilized heparin on cell activation and thrombin generation in a novel, well controlled model of cardiopulmonary bypass. Methods: The model u sed consisted of a heparin-bonded and a non-bonded cardiopulmonary byp ass circuit perfused in tandem with the same unit of Fresh heparinized (3.3 U/ml) human blood for a period of 6 h. Samples were taken for an alysis from the bag just prior to perfusion and at 30, 60, 120 and 360 min of perfusion. Whole blood was used to analyse platelet and white blood cell count, haematocrit and activated coagulation time. Plasma s amples were prepared for batch analysis of the cell activation markers p-selectin, elastase and interleukin-8, and the thrombin generation m arkers thrombin-antithrombin and prothrombin fragment F1 + 2. A sample of tubing was taken from each circuit at the end of the perfusion and prepared for visualization by scanning electron microscopy. Results: Platelet counts were significantly reduced in the non-bonded circuits compared with the heparin-bonded circuits at 30 (22 versus 200 x 10(9) /L P < 0.01), 60 (26 versus 133 x 10(9)/L P < 0.01) and 120 min (28 ve rsus 193 x 10(9)/L P < 0.01 as were white blood cell counts at 30 (1.5 versus 2.7 x 10(9)/L P < 0.01), 60 (0.9 versus 2.4 x 10(9)/L P < 0.01 ), 120 (0.9 versus 1.8 x 10(9)/L P < 0.01) and 360 min (0.4 versus 0.9 x 10(9)/L P < 0.05). The concentration of p-selectin was found to be significantly higher in the non-bonded circuits than in the heparin-bo nded circuits at 30 (37 versus 29 ng/ml P < 0.01), 60 (37 versus 28 ng /ml P < 0.01), 120 (42 versus 27 ng/ml P < 0.01) and at 360 min (72 ve rsus 46 ng/ml P < 0.01), Elastase was elevated in the non-bonded circu its at 30 (570 versus 145 mu g/l P < 0.01), 60 (646 versus 278 mu g/l P < 0.01) and 120 min (613 versus 403 mu g/l P < 0.05) and interleukin -8 at 120 (705 versus 520 pg/ml P < 0.05) and 360 min (11 326 versus 9 910 pg/ml P < 0.05). A similar picture was found for the thrombin gene ration markers. Thrombin-antithrombin complexes were raised in the non -bonded circuits compared with heparin-bonded circuits at 60 (24 versu s 13 mu g/l P < 0.05) and 120 min (46 versus 17 mu g/l P < 0.05) as wa s prothrombin Fragment F1 + 2 at 30 (1.1 versus 0.7 nmol/l P < 0.01), 60 (1.3 versus 0.7 nmol/l P < 0.01), 120 (1.8 versus 0.9 nmol/l P < 0. 01) and 360 min (15.0 versus 13.6 nmol/l P < 0.05). Scanning electron microscopy revealed a greater amount of adherent material on the non-b onded surface relative to the heparin-bonded surface. Conclusions: In a cardiopulmonary bypass circuit perfused with human blood the activat ion of platelets and white blood cells has been seen to be significant ly reduced in the presence of a heparin-bonded surface. Thrombin gener ation due to contact activation of the intrinsic coagulation pathway i s also reduced. (C) 1997 Elsevier Science B.V.