Microcirculatory Hemodynamics after Acute Blood Loss Followed by Fresh and Banked Blood Transfusion

Blood transfusion after blood loss can enhance oxygen delivery to tissues by improving red blood cells' oxygen-carrying capacity. However, it is uncertain whether blood transfusion alleviates the harmful effects of hypoxia at a microcirculatory level. The objective of this study was to evaluate the acute effects of fresh blood transfusion on microcirculatory hemodynamics following blood loss.

Intravital observation of microcirculatory hemodynamics was performed using the rat cremaster muscle flap model. Lewis rats were divided into the following groups (n = 8/group): 1) normovolemic controls; 2) acute blood loss induced by withdrawal of 1 ml of blood; 3) fresh blood transfusion after acute blood loss (1 ml); 4) one-day stored blood transfusion after acute blood loss (1 ml); 5) 1-week stored blood transfusion after acute blood loss (1 ml); and 6) 2-week stored blood transfusion after acute blood loss (1 ml). Blood oxygen saturation, tissue PO₂, temperature, and microcirculatory hemodynamic parameters (blood velocity, vessel diameter, functional capillary perfusion, RBC deformability, and leukocyte-endothelial interaction) were monitored before and after transfusion for 5 hr. After observation, the flaps were harvested and stained with H&E for inflammation and assayed for tissue hypoxia by immunohistochemistry (Hypoxyprobe). Statistical analysis was performed using repeated measures ANOVA, with Bonferroni corrected significance criterion for multiple measurements (significance level of 0.05/3 = 0.017).

There were no significant differences in vessel diameters and RBC velocities among the experimental groups. Capillary density was significantly higher in the fresh blood group in the 2nd and 3rd hour after transfusion. There were a significantly higher number of leukocytes after transfusion. Two-week stored blood had a higher number of rolling leukocytes and lymphocytes, and also more perivascular inflammatory reaction. Tissue oxygenation levels were significantly improved after fresh blood transfusion (p = 0.02). Time of storage had an effect on the RBC ability to delivery oxygen to the tissues. Animals in the two-week stored blood transfusion group presented the lower tissue oxygenation levels.

Fresh blood transfusion was shown to be superior to stored blood due to the maintenance of higher tissue oxygenation levels. Stored blood transfusion, in particular 2-week stored blood, had a restricted capacity of restoring tissue oxygenation levels. It also induced more inflammation and immunologic reaction. Based on these findings, stored blood transfusion should be avoided in elective reconstructive procedures in plastic surgery.