In-vitro hypocoagulability on whole blood thromboelastometry associated with in-vivo expansion of red cell mass in an equine model.

This article highlights a study investigating the impact of an increase in red blood cells (transient polycythemia) induced by phenylephrine on whole blood thromboelastometry results in horses, showing that thromboelastometry results are less coagulable during the polycythemic phase with no change in other coagulation parameters.

Objective of the Study and Methodology

• The primary objective of this study was to assess the relationship between a temporary increase in the circulating red cell mass (RCM), induced by polycythemia, and thromboelastometry results. This was studied using a horse model as horses are known to have a reliable and temporary increase in polycythemia when infused with phenylephrine.
• The experiment involved six healthy research horses. After the recalcification of citrated samples, whole blood thromboelastometry was conducted with both contact activator and tissue factor initiation.
• Apart from these, additional samples were also taken to carry out several other analyses including complete blood count biochemical analysis, activated partial thromboplastin time (aPTT), prothrombin time (PT), and fibrinogen. Additionally, some samples were frozen for thrombin-antithrombin (TAT).

Process and Results

• Additional blood samples were obtained at 5 minutes and 2 hours post phenylephrine infusion, which induced transient polycythemia.
• Results showed that red cell count and hematocrit levels were significantly higher at 5 minutes post phenylephrine infusion compared to the initial baseline and at 2 hours post infusion.
• No changes were noticed in the platelet count, fibrinogen, PT, aPTT, or TAT at any of the given time points. On the other hand, both ex-tem and in-tem parameters were observed to be hypocoagulable at 5 minutes after phenylephrine as compared to baseline and 2 hours.
• A separate thromboelastometry test conducted on four horses, not treated with phenylephrine, showed that spiking the samples with phenylephrine ex-vivo (outside the body) did not have any effect on any of the thromboelastometry parameters.
• Based on these findings, the researchers concluded that whole blood thromboelastometry results were less coagulable only during the polycythemic phase. This points to a potential artifact of thromboelastometry or could indicate the occurrence of true in-vivo hypocoagulability in patients with increased RCM circulation.