Acidosis in Human Whole Blood Does Not Necessarily Impair the Coagulation and the Effect of RFVIIa.

Introduction: Acidosis is associated with high mortality in trauma patients. Therefore there is a major interest in generating acidosis models in vitro and in vivo to determine the effect of acidosis on coagulation and to develop treatments. The aim of this study was to examine the effect of acidosis induction in human whole blood using HCl versus Hepes and to analyze the subsequent effect of rFVIIa (NovoSeven®). Materials and

Methods: Native human whole blood was obtained from healthy volunteers (n=6) and pH was adjusted to 6.8 using 1 M HCl or 1 M Hepes (pH 6.8). Coagulation was triggered with kaolin or tissue factor (TF, Innovin, final dilution 1:42500) and measured by thrombelastography (TEG, Haemoscope®). Furthermore, the effect of rFVIIa (25nM ∼ 90 mcg/kg) was measured. The TEG parameters R (sec), angle (deg) and maximum amplitude (MA, mm) were recorded and presented as mean±SD. A shorter R and greater angle and MA values are indicative of a more robust clot formation. Statistical analysis was performed by a two-way ANOVA-model. Platelet function was analyzed by platelet aggregation using Multiplate (Dynabyte Medical). Exposure of P-selectin, negatively charged phospholipids (annexin A5 binding) and induction of the active conformation of the fibrinogen receptor GPIIb/IIIa (PAC-1 binding) on platelets after TRAP-stimulation of whole blood was analyzed using a FACS Canto flow cytometer (BD).

Results: TEG, platelet aggregation and flow cytometry indicated that lowering the pH to 6.8 by HCl affected the blood significantly different than when pH was lowered by addition of Hepes. HCl-treated blood triggered with either kaolin or TF showed a significantly decreased R value (378±45 or 661±130 vs 539±98 or 888±353 in untreated controls), significantly decreased MA (52±6 or 51±9 vs 66±8 or 62±13) and decreased angle (50±7 or 36±10 vs control 57±10 or 44±19, not significant). Hepes-treated blood triggered with kaolin showed no difference in R (458±52), angle (64±4) and MA (58±9) compared to untreated controls, whereas blood triggered with TF showed significantly shortened R-value (461±91) and enhanced angle (63±5) compared to untreated controls. Hepes treatment had no effect on MA (64±12). rFVIIa significantly shortened R irrespective of the acidosis inducer or clot trigger(HCl/kaolin 283±34, HCl/TF 307±52; Hepes/kaolin 363±32, Hepes/TF 313±46). Although the other TEG parameters were also improved, the effect was only significant when blood was treated with HCl and clotting initiated with TF (angle 48±11, MA 56±10). HCl-induced acidosis abolished platelet aggregation, whereas Hepes-induced acidosis did not alter platelet aggregation compared to normal blood. Flow cytometry showed that platelets from HCl-treated blood were pre-activated as evidence by expression of P-selectin on 70% of the platelets, annexin A5 binding to 14% of the platelets and PAC-1 binding to 62% of the platelets before stimulation. TRAP-stimulation increased P-selectin expression, and PAC1 and Annexin A5 binding to platelets in HCl-treated blood. In contrast, Hepes-treatment did not pre-activate the platelets and the increase in P-selectin expression, and annexin A5 and PAC-1 binding after TRAP-stimulation was as seen for control blood.

Conclusion: The method used to lower pH in human blood strongly influences the functionality of the platelets and coagulation factors independent of the final pH. It is therefore important in experimental in vitro and in vivo models to be aware of these dramatically different effects in order to draw correct conclusions.