Subnormothermic Oxygenated Machine Perfusion (24 h) in DCD Kidney Transplantation

Abstract

Background: Ex vivo kidney perfusion is an evolving platform that demonstrates promise in preserving and rehabilitating the kidney grafts. Despite this, there is little consensus on the optimal perfusion conditions. Hypothermic perfusion offers limited functional assessment, whereas normothermic perfusion requires a more complex mechanical system and perfusate. Subnormothermic machine perfusion (SNMP) has the potential to combine the advantages of both approaches but has undergone limited investigation. Therefore, the present study sought to determine the suitability of SNMP for extended kidney preservation.

Methods: SNMP at 22-25 °C was performed on a portable device for 24 h with porcine kidneys. Graft assessment included measurement of mechanical parameters and biochemical analysis of the perfusate using point-of-care tests. To investigate the viability of kidneys preserved by SNMP, porcine kidney autotransplants were performed in a donation after circulatory death (DCD) model. SNMP was also compared with static cold storage (SCS). Finally, follow-up experiments were conducted in a subset of human kidneys to test the translational significance of findings in porcine kidneys.

Results: In the perfusion-only cohort, porcine kidneys all displayed successful perfusion for 24 h by SNMP, evidenced by stable mechanical parameters and biological markers of graft function. Furthermore, in the transplant cohort, DCD grafts with 30 min of warm ischemic injury demonstrated superior posttransplant graft function when preserved by SNMP in comparison with SCS. Finally, human kidneys that underwent 24-h perfusion exhibited stable functional and biological parameters consistent with observations in porcine organs.

Conclusions: These observations demonstrate the suitability and cross-species generalizability of subnormothermic machine perfusion to maintain stable kidney perfusion and provide foundational evidence for improved posttransplant graft function of DCD kidneys after SNMP compared with SCS.

FIGURE 1.

Subnormothermic ex vivo kidney perfusion using an automated, portable perfusion platform (OrganBank Transport device supplied by BMI OrganBank). A, Cartoon schematic depicts the perfusion circuit used in this study. The perfusate is oxygenated with a gas mix (95% O₂, 5% CO₂). The flow is continuous and adjusted automatically based on pressure readings to achieve a constant pressure of 60–70 mm Hg. Urine is collected externally and then recirculated into the perfusate. B, Perfusion device is fully portable and easily accommodated on a standard benchtop. C, Porcine kidney is shown undergoing oxygenated subnormothermic machine perfusion (SNMP) using the device.

FIGURE 2.

Cartoon schematic of the porcine autotransplant procedure. A, On operative day 1, pigs underwent donor nephrectomy. DCD kidneys were subjected to 30 min of warm ischemia before preservation by SCS or SNMP. B, Following 24 h of SCS or SNMP, the pig was again anesthetized, the kidney autotransplant was performed, and the contralateral kidney was removed. C, Pigs were subsequently monitored for 3 or 7 d postsurgery and the analysis of blood chemistry was conducted periodically. DCD, donation after circulatory death; SCS, static cold storage; SNMP, subnormothermic machine perfusion.

FIGURE 3.

Mechanical perfusion parameters in LD and DCD porcine kidneys. A, Input pressure was maintained at 65–70 mm Hg for the duration of perfusion. B, Vascular resistance remained stable for LD kidneys, which, was similarly observed in DCD kidneys despite an initial period of elevated resistance. C, Target flow of 300–350 mL/min was achieved in both groups within 3 h of perfusion and remained stable for the duration of perfusion. D, Both LD and DCD kidneys exhibited healthy gross morphology after 24 h of perfusion and after reperfusion with RBCs. E, Pre- and postperfusion graft weights were comparable in a subset of LD and DCD kidneys. Postperfusion weight increased by approximately 50% in both groups, indicative of modest edema. DCD, donation after circulatory death; LD, living donor; RBC, red blood cell. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.

FIGURE 4.

Biochemical analysis of circulating perfusate during 24 h. A, LD and DCD groups displayed similar increases in sodium concentration in the perfusate over time, reaching a peak of ~155 mM at 24 h (P < 0.001). B, Similarly, despite a main effect of time, no significant difference in potassium levels between LD and DCD groups was observed (P = 0.311). C, iCal concentration displayed a modest decline in both groups but otherwise remained within tolerable limits (P < 0.0001). D, Lactate remained stable for approximately 12 h, after which modest accumulation was observed in both LD and DCD groups (P < 0.001). E, Bicarbonate concentration similarly accumulated during the course of perfusion equally between groups (P < 0.0001). F, Although perfusate lactate and bicarbonate moderately increased over time, pH remained largely stable, ending in the range of ~7.3–7.4, well within tolerable physiological limits (P < 0.01). DCD, donation after circulatory death; iCal, ionized calcium; LD, living donor. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.

FIGURE 5.

Functional tests of graft viability. A and B, In a subset of perfused kidneys, perfusate levels of creatinine and BUN are quantified during the 24-h period. As shown in panel A, creatinine remained stable during perfusion and well within tolerable limits, indicative of adequate glomerular filtration. BUN, however, displayed significant accumulation after 6 h of perfusion, reaching a peak concentration of ~15 mg/dL but within the typical range of arterial and venous levels (eg, 8–26; P < 0.0001). C, Concentration of AST increased significantly during the duration of perfusion, indicative of some degree of cell death (P < 0.0001). AST, aspartate aminotransferase; BUN, blood urea nitrogen; DCD, donation after circulatory death; LD, living donor. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.

FIGURE 6.

Assessment of graft function over time after porcine kidney autotransplantation. A, Analysis of serum creatinine revealed a significant main effect of the preservation method, with SNMP kidneys exhibiting reduced serum creatinine overall posttransplant (P = 0.018). B, In addition to creatinine, animals in the DCD SNMP group displayed significantly lower BUN relative to SCS (P = 0.023). C, Circulating potassium also remained stable in both groups throughout the 7-d postoperative period. BUN, blood urea nitrogen; DCD, donation after circulatory death; SCS, static cold storage; SNMP, subnormothermic machine perfusion. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.