Haemodilution-induced changes in coagulation and effects of haemostatic components under flow conditions

Abstract

Background: Blood flow patterns are important modifiers of platelet interactions with plasma coagulation factors. However, it is not feasible to evaluate rheological effects of haemodilution on coagulation using conventional coagulation testing.

Methods: We evaluated thrombus formation with a microchip-based flow-chamber system using whole blood from 12 healthy volunteers (with/without 40% dilution with saline), and 15 cardiac patients [before/after cardiopulmonary bypass (CPB)] in parallel with thromboelastometry. The in vitro additions of von Willebrand factor (vWF, 1.5 U ml(-1)), prothrombin complex concentrate (PCC, 0.3 U ml(-1)), fibrinogen (2 g litre(-1)), or combined PCC (0.3 U ml(-1)) and fibrinogen (1 g litre(-1)) were examined. Recalcified whole-blood samples were perfused over the microchip coated with collagen and tissue thromboplastin at flow rates of 10 and 3 µl min(-1).

Results: Dilution of whole blood led to delayed onset of thrombus formation (Ton), and thrombus growth (T80). Changes relative to baseline values were more extensive at 10 µl min(-1) (≥85% prolongation for Ton and T80) than at 3 µl min(-1) (≥40% prolongation for Ton and T80). Adding vWF accelerated thrombus formation only at 10 µl min(-1), while PCC increased thrombin generation in the thrombus at both flow rates. Fibrinogen increased mural thrombus formation at 3 µl min(-1). Decreased clot strength after dilution was restored by fibrinogen, but not by vWF or PCC on thromboelastometry. Additive effects of fibrinogen and PCC in post-CPB blood were demonstrated by both flow chamber and thromboelastometry.

Conclusions: Blood flow affects thrombus formation after haemodilution and subsequent haemostatic component interventions, with differential effects at low and high flow.

Keywords: cardiopulmonary bypass; fibrinogen; flow chamber; haemodilution; haemostasis.