Urine Recirculation Improves Hemodynamics and Enhances Function in Normothermic Kidney Perfusion

The study compares urine recirculation (URC) to urine replacement (UR) with Ringer’s lactate in a porcine normothermic kidney machine perfusion (NMP) model using a preclinical prototype device. METHODS. Kidney pairs were recovered uninjured (as live-donor nephrectomy) and perfused consecutively. Pig kidneys (n = 10) were allocated to either NMP with URC (n = 5) or NMP with volume replacement (n = 5). Cold ischemia time was either 2 or 27 hours for the first or second perfusion (URC or UR) of a kidney pair. An autologous blood-based perfusate, leukocyte-filtered, was used and NMP performed up to 24 hours. Perfusion parameters, biochemistry/metabolic parameters were monitored and samples collected. RESULTS. Physiological mean arterial pressures and flows were achieved in both groups but were sustainable only with URC. Significantly higher arterial flow was observed with URC (326.7 ± 1.8 versus 242.5 ± 14.3 mL/min, P = 0.001). Perfusate sodium levels were lower with URC, 129.6 ± 0.7 versus 170.3±2.7 mmol/L, P < 0.001). Stable physiological pH levels were only observed with URC. Perfusate lactate levels were lower with URC (2.2 ± 0.1 versus 7.2 ± 0.5 mmol/L, P < 0.001). Furthermore, the hourly rate of urine output was lower with URC and closer to physiological levels (150 versus 548 mL/h, P = 0.008). Normothermic kidney perfusion with URC was associated with longer achievable durations of perfusion: the objective in all experiments was a 24-hour perfusion, but this was not achieved in every case. The mean perfusions were 17.3 ± 9.2 hours with URC versus 5.3 ± 1.3 hours NMP with UR; P = 0.02. There appeared to be no differences in baseline tubular condition with and without URC. CONCLUSIONS. URC facilitates long-term kidney NMP in a porcine model. Perfusate homeostasis and stability of renal arterial flow throughout the perfusion period was only achievable with URC, independent of cold ischemia time duration.