Oxygenating the microcirculation: the perspective from blood transfusion and blood storage.

Tissue oxygen delivery depends on red blood cell (RBC) content and RBC flow regulation in the microcirculation. The important role of the RBC in tissue oxygenation is clear from anaemia and the use of RBC transfusion which has saved many lives. Whether RBC transfusion actually restores tissue oxygenation is difficult to determine due to the lack of appropriate clinical monitoring techniques. Some patients with restored haemoglobin levels and stable haemodynamics still develop tissue hypoxia, emphasizing that, in addition to global parameters, local microcirculatory control mechanisms are also important in the restoration of tissue oxygenation. Both clinical and animal experimental studies have indicated that storage of RBC diminishes their ability to oxygenate the tissue. Several intrinsic RBC parameters that change during storage and might influence tissue oxygenation will be mentioned. The release of vasodilators from RBC that will alter blood flow during hypoxia, mediated by haemoglobin in the RBC that functions as an oxygen sensor, could be impaired during storage. A better understanding of hypoxia-induced vasodilator release from RBC might become a potential target for drug development and improve tissue oxygenation after transfusion.