Effects of Suspension Osmolarity on Rbc Mechanical Properties and Shear Induced Hemolysis

INTRODUCTION Storage of human red blood cells (RBCs) began around 1910 when the anticoagulant properties of citrate were discovered. Over the last century, RBC storage techniques were improved so patients can receive healthy RBCs after longer storage periods. Today, about 80 million transfusions per year are performed worldwide [1,2]. Many parameters, such as temperature and nutrient concentrations, must be controlled for RBC storage to be successfully. To control these parameters, RBCs are stored in preservative solutions, such as CPDA-1 or AS-5, which have osmolarities higher than physiological osmolarity. The solutions currently in use allow RBCs to be stored up to 42 days [3]. Despite these preservation techniques, RBC properties change during storage. Previous studies have shown that RBCs are less deformable, have a lower gas carrying capacity, and do not survive long in circulation after a period of storage [1,4,5]. Zehnder et al. demonstrate that RBCs stored in hypertonic conditions had higher hemolysis, osmotic fragility, and viscosity in addition to having lower deformability and aggregability [6]. These results suggest that the osmolarity of the RBC suspension may contribute to the changes in RBC properties during storage. However, none of these studies have examined how RBCs in high osmolarity respond to exposure to shear stress. Patients who receive older RBC units are more likely to experience serious complications such as renal failure, respiratory insufficiency, multi-organ failure, and in-hospital death [2]. RBCs’ short lifetime after transfusions suggests that stored RBCs are more susceptible to shear stress than normal cells. This can have serious consequences in a patient with a device such as a left ventricle assist device (LVAD). These devices can apply shear stresses on RBCs that are higher than physiological shear stresses [7].