Transfusion of Red Blood Cells under Shock Conditions in the Rat Microvasculature.

Background RBC transfusion is the mainstay of therapy for resuscitation of patients with hemorrhagic shock. Ex-vivo storage of RBCs for transfusions is associated with a storage lesion which decreases erythrocyte deformability and increases their adhesiveness to vascular endothelium. This may impair microcirculatory flow with deleterious effects on oxygen delivery post-transfusion. The objective of this study was to determine whether transfused stored rat blood impairs the microcirculation following resuscitation from hemorrhagic shock

Methods Donor Sprague Dawley rat RBCs were collected and stored in CPDA-1 under standard blood bank conditions. RBCs were labelled with FITC (fluorescein isothiocyanate) 24 hours before the experiment. RBCs stored for less than 24 hours (fresh) RBCs (n=3) were compared to RBCs stored for 7 days (n=3). To induce shock, forty percent of blood volume was removed from male Sprague Dawley rats. Animals were then resuscitated by injecting 1.5mL of labelled packed RBCs and sufficient saline to restore blood volume via arterial line. The number of adherent labelled RBCs in the extensor digitorum longus muscle (EDL) was detected using intravital video microscopy (20X magnification). RBC velocity, capillary diameters, capillary Hct (hematocrit), arterial Hct, and lactate data was collected at three time points (baseline, shock and resuscitation).

Results Lactate levels increased significantly during shock in both the fresh and stored groups. Arterial Hct decreased in shock and was restored to baseline levels with resuscitation. The stored group had an increased number of stopped cells in the microcirculation compared to their fresh counterparts (p=0.004). There was no statistical significant difference in capillary diameters between groups or time points. Both groups showed an increase in RBC velocity from baseline to resuscitation (stored group doubled, fresh group tripled). Capillary Hct did not change in the fresh group but doubled in the old group from baseline to resuscitation.

Conclusion In our shock model, transfusion of stored RBCs resulted in an increased number of stopped cells and lower RBC velocity in capillaries as compared to fresh RBCs. Stored RBCs also had an increased capillary Hct from baseline to resuscitation and a diminished hyperemic response as compared to fresh RBCs. We conclude that stored RBCs following transfusion behave differently than native or fresh transfused cells in the microcirculation. Further studies are needed to determine the impact of these microcirculatory changes on oxygen availability in transfusion.