The effect of warm ischemic time on renal function and injury in the isolated hemoperfused kidney

BACKGROUND: The precise effect of warm ischemia on renal allograft function remains unclear and leads to variable warm ischemic time (WIT) limits advocated by transplant programs. This study aims to investigate the relationship between WIT, renal ischemia reperfusion injury, and graft function using a hemoperfused kidney model. METHODS: Porcine kidneys were perfused with normothermic blood on an isolated organ perfusion system. Kidneys were divided into four groups (n=6) and subjected to 7, 15, 25, and 40 min WIT. Physiological parameters were measured throughout the 6 hr perfusion period. Serum, tissue, and urine samples were analyzed for histological and biochemical markers of ischemia reperfusion injury. RESULTS: Creatinine clearance, urine output, renal hemodynamics, and oxygen consumption deteriorated proportionally with increasing WIT. A significant increase in plasma carbonyl levels during perfusion was seen after 25 and 40 min WIT only. Plasma 8-isoprostane levels were higher after 40 min WIT (2.5+/-1.6) vs. 7, 15, and 25 min WIT (0.65+/-0.43, 0.25+/-0.12, and 0.62+/-0.21, respectively; P<0.05). A negative correlation was shown between urine output and plasma carbonyls (r=-0.415, P<0.05) and between 8-isoprostane levels and creatinine clearance (r=-0.649, P<0.005). Caspase-3 activity was significantly higher after 7 min WIT compared with the other groups, correlating positively with creatinine clearance, urine output, and renal blood flow. CONCLUSION: The isolated organ perfusion system successfully delineated a clear WIT-dependent variation in renal function which correlated accurately with oxidative injury markers. This model may represent a clinically applicable tool for assessing graft viability.