Prolonged Ex Vivo Normothermic Machine Perfusion of an Uncontrolled Donation After Circulatory Death Kidney Graft Using a Hemoglobin-Based Oxygen Carrier beyond 53 Hours

Background : Normothermic machine perfusion (NMP) has emerged as a promising technology in organ transplantation by enabling physiological preservation, real-time viability assessment, and therapeutic intervention during ex vivo organ maintenance. Although prolonged ex vivo preservation has been successfully achieved in liver transplantation, the application of NMP in kidney grafts remains limited, particularly for marginal kidneys from uncontrolled donation after circulatory death (uDCD) donors. Extending kidney preservation time may facilitate long-distance organ transportation, improve the utilization of marginal grafts, and provide a platform for graft repair and pre-transplant therapeutic interventions. Methods : We developed a portable normothermic kidney perfusion system using a hemoglobin-based oxygen carrier (HBOC) instead of human red blood cells and performed prolonged ex vivo preservation of a discarded left kidney graft from a uDCD donor. Hemodynamic parameters, biochemical profiles, urine production, and histological changes associated with kidney injury and inflammation were continuously evaluated during perfusion. The contralateral kidney preserved with University of Wisconsin (UW) solution at 4°C served as a cold storage control. Results : The kidney graft was successfully maintained under NMP for 53 hours with stable perfusion conditions. Mean perfusion pressure and flow were maintained at 62.38 ± 7.51 mmHg and 125.13 ± 20.40 mL/min, respectively, with perfusate temperature maintained between 32.5°C and 33.5°C. The renal vascular resistance index remained stable (0.50 ± 0.12 mmHg/mL/min). The HBOC-based oxygen delivery system maintained adequate oxygenation throughout perfusion. Perfusate creatinine levels remained relatively stable, while lactate levels initially increased and subsequently returned to normal levels after prolonged perfusion, suggesting recovery of renal metabolic activity. Cumulative urine output reached 1267 mL by the end of perfusion. Histological evaluation demonstrated no significant progression of glomerulosclerosis, tubular atrophy, or interstitial fibrosis. Compared with cold storage, NMP was associated with reduced progression of tubular injury, although mild tubular degeneration and inflammatory changes developed during prolonged perfusion. After approximately 32 hours of perfusion, renal resistance, blood flow, biochemical parameters, and histological findings demonstrated progressive improvement, whereas deterioration was observed with further extension of perfusion duration. however, they gradually deteriorated after 32 hours. Conclusion: This study demonstrates the feasibility of prolonged blood-free normothermic machine perfusion for maintaining the viability of a marginal uDCD kidney graft for more than 53 hours ex vivo. HBOC-based NMP may provide a promising platform for extended kidney preservation, real-time graft assessment, and future development of organ repair strategies. Further studies using larger cohorts and transplantation models are required to validate its clinical applicability. it is recommended that the perfusion preservation time of ex vivo kidneys should not exceed 32 hours.