An in vitro model for hemostasis monitoring during simulated cardiopulmonary bypass

The optimum model for hemostasis monitoring during cardiopulmonary bypass (CPB) is the evaluation of physiologic changes in the intact organism. This is often logistically difficult and expensive. The purpose of this study was to design an in vitro model of blood coagulation for use in simulated CPB. Human expired blood components within 4 days of outdating were reconstitituted as follows: 4 units of packed red blood cells, 4 units of platelets, and 3 units of fresh frozen plasma. The mixture was circulated in a simulated extracorporeal circuit. Blood samples were drawn every 30 minutes over a 2 hour period, recalcified, and analyzed for platelet count (PL T), fibrinogen concentration (FIB), prothrombin time (PT), activated partial thromboplastin time (aPTT), celite and kaolin activated clotting times (ACT), and thrombelastography (TEG). In the four different coagulation monitors utilized, there were no significant changes in celite or kaolin ACTs. PT increased from 15.8 ± 1.1 sec to 25.2 ± 7.8 sec and aPTT from 62.1 ± 15.9 sec to 78.9 ± 36.5 sec (p = NS). There were no changes in either PL T count or FIB concentration. Both celite and tissue factor activated TEG values trended towards hypocoagulability. In conclusion, the results show that the in vitro model is stable over 120 min of recirculation time within a simulated cardiopulmonary bypass circuit in regards to platelet count, hematocrit, total protein, PT, aPTT, and ACT. Further examination will be necessary to establish the effects of the model in regard to platelet function.