Hypothermic Oxygenated Machine Perfusion in Porcine Donation After Circulatory Determination of Death Liver Transplant

Controlled oxygenated rewarming of cold stored liver grafts by thermally graduated machine perfusion prior to reperfusion

The quality of cold-stored livers declines with the extension of ischemic time, increasing the risk of primary dys or nonfunction. A new concept to rescue preserved marginal liver grafts by gentle oxygenated warming-up prior to blood reperfusion was investigated. Porcine livers were preserved by cold storage (CS) in modified HTK-solution for 18 h. Some grafts were subsequently subjected to 90 min of controlled oxygenated rewarming (COR) by machine perfusion with gradual increase of perfusate temperature up to 20°C or simple oxygenated machine perfusion in hypothermia (HMP) or subnormothermia (SNP). Graft viability was assessed thereafter by 4 h of normothermic blood reperfusion ex vivo. Endischemic tissue energetics were significantly improved by COR or SNP and to a notably lesser extent by HMP. COR significantly reduced cellular enzyme loss, gene expression and perfusate activities of TNF-alpha, radical mediated lipid peroxidation (LPO) and increase of portal vascular perfusion resistance upon reperfusion, while HMP or SNP were less protective. Only COR resulted in significantly more bile production than after CS. Histological injury score and caspase 3-activation were significantly lower after COR than after CS. Oxygenated rewarming prior to reperfusion seems to be a promising technique to improve subsequent organ recovery upon reperfusion of long preserved liver grafts.

Ex vivo normothermic machine perfusion and viability testing of discarded human donor livers

In contrast to traditional static cold preservation of donor livers, normothermic machine perfusion may reduce preservation injury, improve graft viability and potentially allows ex vivo assessment of graft viability before transplantation. We have studied the feasibility of normothermic machine perfusion in four discarded human donor livers. Normothermic machine perfusion consisted of pressure and temperature controlled pulsatile perfusion of the hepatic artery and continuous portal perfusion for 6 h. Two hollow fiber membrane oxygenators provided oxygenation of the perfusion fluid. Biochemical markers in the perfusion fluid reflected minimal hepatic injury and improving function. Lactate levels decreased to normal values, reflecting active metabolism by the liver (mean lactate 10.0 ± 2.3 mmol/L at 30 min to 2.3 ± 1.2 mmol/L at 6 h). Bile production was observed throughout the 6 h perfusion period (mean rate 8.16 ± 0.65 g/h after the first hour). Histological examination before and after 6 h of perfusion showed well-preserved liver morphology without signs of additional hepatocellular ischemia, biliary injury or sinusoidal damage. In conclusion, this study shows that normothermic machine perfusion of human donor livers is technically feasible. It allows assessment of graft viability before transplantation, which opens new avenues for organ selection, therapeutic interventions and preconditioning.

Protective mechanisms of end-ischemic cold machine perfusion in DCD liver grafts

BACKGROUND & AIMS

The aim of this study was to identify protective mechanisms of cold machine perfusion in liver grafts donated after cardiac death.

METHODS

Pig livers exposed to 60-min warm ischemia were cold stored for 7 h or treated after 6-h cold storage with 1-h hypothermic oxygenated perfusion (HOPE) through the portal vein. Different physical (perfusion pressure) and chemical (oxygen, mitochondrial transition pore inhibition) parameters were analyzed during machine perfusion to dissect key steps of mechanism.

RESULTS

HOPE treatment led to a significant slowdown of mitochondrial respiration rate during 1-h machine perfusion. After reperfusion following low pressure HOPE, mitochondrial injury, nuclear injury, Kupffer cell activation and endothelial injury were significantly improved, as tested on an isolated liver perfusion model. In contrast, machine perfusion with deoxygenated perfusate showed no protection from hepatocyte injury and Kupffer cell activation. However, endothelial injury was also prevented by low pressure machine perfusion in the absence of oxygen. Perfusion with higher pressure provoked endothelial damage and Kupffer cell activation.

CONCLUSIONS

The mechanisms of protection by hypothermic machine perfusion appear to be at least twofold. First, oxygenation under hypothermic conditions protects from mitochondrial and nuclear injury by downregulation of mitochondrial activity before reperfusion. Second, cold perfusion itself, under low pressure conditions, prevents endothelial damage, independently of oxygen.