Localized antithrombotic but minimal systemic coagulation effects of sodium bicarbonate in mechanical circulatory support.

Sodium bicarbonate has recently emerged as an alternative additive to purge flow in microaxial blood pumps, offering local antithrombotic effects. However, the systemic effects of additive bicarbonate on coagulation remain incompletely defined. Here, we examined the effect of sodium bicarbonate at varying concentrations (10- 2-10- 5M) on select coagulation parameters to define systemic versus local effects. Fresh human whole blood from healthy adults (N ≥ 4 per assay) was incubated with sodium bicarbonate over a range of concentrations (10- 5-10- 2M). Coagulation and thrombus formation was assessed via whole blood clotting time (WBCT), activated partial thromboplastin time (aPTT), prothrombin time (PT), rotational thromboelastometry (ROTEM) and total thrombus analysis (T-TAS). Sodium bicarbonate at concentrations 10- 3M or less, did not induce significant changes in WBCT, aPTT, PT, ROTEM clot stiffness, or thrombus formation. Notably, at higher bicarbonate concentrations (10- 2M) WBCT was delayed (2.5 ± 0.5 min; p = 0.02), aPTT showed a moderate delay (3.9 ± 2.2 s; p > 0.05), ROTEM revealed increased clot stiffness at 10 min (1.7 ± 0.3 mm; p = 0.004) with high concentrations (10- 2 M) and a moderate decrease in thrombus formation (33.5 ± 21.9Kpa∙min; p > 0.05). Sodium bicarbonate, at concentrations encountered during intravenous (IV) use or expected systemic dilution during Impella purge use, was not associated with statistically significant alterations in global coagulation or platelet thrombosis in this in vitro study. Supraphysiologic levels, consistent with via intra-device purge flow in the device microenvironment, produced measurable but mild changes to clotting time and stiffness. These findings underscore the safety and lack of confounding effect of low dose systemic bicarbonate on systemic coagulation, while supporting mechanisms of local device-based antithrombotic efficacy.