Physiological effects of altering oxygenation during kidney normothermic machine perfusion

Kidney normothermic machine perfusion (NMP) has historically used a 95% O₂-5% CO₂ gas mixture. Using a porcine model of organ retrieval, NMP, and reperfusion, we tested the hypothesis that reducing perfusate oxygenation ( $$ ) would be detrimental to renal function and cause injury. In the minimal ischemic injury experiment, kidneys sustained 10 min of warm ischemia and 2 h of static cold storage before 1 h of NMP with either 95%, 25%, or 12% O₂ with 5% CO₂ and N₂ balance. In the clinical injury experiment, kidneys with 10-min warm ischemia and 17-h static cold storage underwent 1-h NMP with the above gas combinations or 18-h static cold storage as a control. They were then reperfused with whole blood and 95% O₂ for 3 h. Overall, reducing $$ did not significantly influence renal function in either experiment. Furthermore, there were no differences in the injury markers urinary neutrophil gelatinase-associated lipocalin or tissue high-motility group box protein 1. In the minimal ischemic injury experiment, a $$ of 25% significantly reduced renal blood flow and increased vascular resistance. Oxygen delivery, consumption, and extraction (oxygen extraction ratio) were significantly greater at 95% $$ . In the clinical injury experiment, renal blood flow was significantly increased at 25% $$ and Na⁺ excretion decreased. At 95% $$ , the oxygen content and oxygen extraction ratio were significantly increased. During reperfusion, renal blood flow was significantly increased in the 25% group. The control group pH was significantly decreased compared with the 25% group. Our data suggest that reducing $$ during NMP does not have detrimental effects on renal function or markers of injury.