Hemostatic properties of whole blood : A series of in vitro studies

Whole blood has reemerged in the treatment of hemodynamically unstable bleeding patients due to easier logistics and potentially superior hemostatic properties compared to component therapy. The hemostatic effectiveness is attributed to lesser dilution caused by preservative solutions and active, cold-stored platelets. In addition to easier logistics, the presence of platelets is a key factor in the suitability of whole blood to prehospital situations, where platelets are otherwise unavailable. In these four in vitro studies on the hemostatic properties of whole blood, we compared whole blood with current in-hospital and prehospital component therapies, explored the extracellular vesicle content of aging blood products, studied whether whole blood properties are retained in room temperature storage for over 24 hours, and how the properties of leukoreduced and non-leukoreduced whole blood change during an extended storage of 35 days. Volunteer blood donors were recruited for the studies. Whole blood was stored in citrate- phosphate-dextrose and refrigerated after leukoreduction at 18-24 hours of room temperature storage, or citrate-phosphate-dextrose-adenine and stored in a refrigerator or room temperature controlled styrofoam containers after donation without leukoreduction. Samples were taken from blood donors for baseline analyses and periodically from blood bags to determine storage-induced changes. The analyses performed included blood count, hemolysis assays, metabolic assays, conventional coagulation assays, viscoelastic assays (thromboelastometry and sonorheometry), and assays for platelet function, thrombin generation, and extracellular vesicle count and origin. We found that in vitro, cold-stored whole blood is hemostatically superior compared to the prehospital component therapy of red blood cells and lyophilized plasma. The component therapy of red blood cells, plasma, and platelets in a balanced 1:1:1 ratio was not inferior to whole blood, especially when whole blood was not fresh. We found that while leukoreduction causes a transient reduction in the hemostatic capacity of cold- stored whole blood, it is similar to non-leukoreduced whole blood by two weeks of storage. The 5-day room temperature storage of non-leukoreduced whole blood does not seem to impair hemostatic capacity. We found that extracellular vesicles accumulate during whole blood storage, during which the declining hemostatic function of whole blood is not compensated by this accumulation. Finally, we observed that the results of clot strength parameters in viscoelastic assays were contradictory, as sonorheometry clot stiffness decreased notably and fell below the detection limit, while thromboelastometry maximum clot firmness decreased only moderately. In conclusion, these studies support the use of prehospital cold-stored whole blood and encourage further research regarding extended room temperature storage. While there may be platelet contribution even in 35-day-old whole blood, clot strength in already 14- day-old whole blood may be weaker than previously thought.