Impact of acid selection on thrombelastometric test results - an in-vitro cohort study

Acidosis is common in critically ill patients and is associated with coagulopathy. The impact of different acids on coagulation remains poorly understood. Hydrochloric acid has often been used without critical evaluation. We aimed to investigate the influence of different acids and their concentrations on rotational thromboelastometry (ROTEM).

In this observational study ten, blood samples were treated with hydrochloric acid (HCl), lactic acid (C₃H₆O₃), phosphoric acid (H₃PO₄), or dihydrogen phosphate (H₂PO₄⁻) to achieve defined pH levels (7.2-6.9). Respiratory acidosis was simulated by incubation in a 20% CO₂ atmosphere. Five additional samples were exposed to varying acid concentrations. Samples were analyzed using the ROTEM EXTEM assay. Clotting time (CT), clot formation time (CFT), α-angle, maximum clot firmness (MCF), and maximum lysis (ML) were assessed.

All acids exhibited concentration-dependent effects on EXTEM parameters. HCl caused significant reductions in MCF and prolonged CFT, indicating impaired clot firmness and propagation. C₃H₆O₃ induced moderate changes, with elevated fibrinolysis at intermediate concentrations. H₃PO₄ reduced MCF and increased ML, while H₂PO₄⁻ primarily delayed clotting initiation and markedly inhibited fibrinolysis. CO₂-induced acidosis (pH ≈ 7.1) led to reduced fibrinolytic activity without affecting CT or MCF. Across acid types, increasing acidity consistently impaired clotting dynamics.

The type of acid inducing acidosis was associated with distinct alterations in ROTEM parameters in vitro. The choice of acid should be carefully considered in experimental models and taken into account when interpreting data. Whether such effects occur in vivo remains uncertain.