Diffusion-limited O₂release in human kidneys perfused with stored blood

ABSTRACT A central dogma in physiology is that oxygen release at tissues is not diffusion-limited because gas exchange at capillaries is rapid. This assertion has influenced clinical care, which focuses on optimising oxygen delivery through improving blood flow and oxygen content, rather than oxygen unloading from red blood cells (RBCs). Since storage of blood causes profound changes that slow oxygen release from RBCs, transfusions could compromise tissue respiration. We investigated this in transplant human kidneys normothermically perfused with stored blood. During perfusions, renal respiration was measured from blood gases and RBCs were analysed for oxygen-unloading kinetics. Respiratory rate did not correlate significantly with the standard definition of oxygen delivery based on blood flow and oxygen content. However, a strong correlation was obtained after introducing a factor describing oxygen release from RBCs. Oxygen release to tissues can become diffusion-limited with transfused blood, and therefore the kinetic quality of RBCs should be considered.