Criteria for viability assessment of discarded human donor livers during ex vivo normothermic machine perfusion

Abstract

Although normothermic machine perfusion of donor livers may allow assessment of graft viability prior to transplantation, there are currently no data on what would be a good parameter of graft viability. To determine whether bile production is a suitable biomarker that can be used to discriminate viable from non-viable livers we have studied functional performance as well as biochemical and histological evidence of hepatobiliary injury during ex vivo normothermic machine perfusion of human donor livers. After a median duration of cold storage of 6.5 h, twelve extended criteria human donor livers that were declined for transplantation were ex vivo perfused for 6 h at 37 °C with an oxygenated solution based on red blood cells and plasma, using pressure controlled pulsatile perfusion of the hepatic artery and continuous portal perfusion. During perfusion, two patterns of bile flow were identified: (1) steadily increasing bile production, resulting in a cumulative output of ≥ 30 g after 6 h (high bile output group), and (2) a cumulative bile production <20 g in 6 h (low bile output group). Concentrations of transaminases and potassium in the perfusion fluid were significantly higher in the low bile output group, compared to the high bile output group. Biliary concentrations of bilirubin and bicarbonate were respectively 4 times and 2 times higher in the high bile output group. Livers in the low bile output group displayed more signs of hepatic necrosis and venous congestion, compared to the high bile output group. In conclusion, bile production could be an easily assessable biomarker of hepatic viability during ex vivo machine perfusion of human donor livers. It could potentially be used to identify extended criteria livers that are suitable for transplantation. These ex vivo findings need to be confirmed in a transplant experiment or a clinical trial.

Figure 1. Cumulative bile production during ex vivo normothermic machine perfusion of human donor livers.

Presented are individual values for 12 livers that were declined for transplantation. Ex vivo machine perfusion and viability testing was started after a median cold storage of 6.5 hours. Two distinct patterns of bile flow could be identified: 1) a steadily increasing bile production, resulting in a cumulative bile output of ≥30 g during the 6 h of perfusion (green lines), and 2) an initially increasing bile production during the first 2–3 hours, followed by a diminishing production, resulting in a cumulative bile production in 6 h <20 g (red lines).

Figure 2. Changes in portal flow (panel A) and arterial flow (panel B) during ex vivo normothermic machine perfusion of human donor livers, using a pressure controlled device.

Flow in the portal vein and hepatic artery increased rapidly during the first 30 min and flows remained stable thereafter for the entire 6 h perfusion period. There were no significant differences in portal flow and although median arterial flow was constantly lower in livers with a low bile output, compared to the high bile output group, this did not reach statistical significance.

Figure 3. Changes in hepatic energy content as reflected by hepatic ATP content.

In contrast to livers with low bile output, livers in the high bile output group showed a significantly higher hepatic ATP content during the course of NMP. (AUC p = 0.04).

Figure 4. Histology of livers after 6 hours of normothermic machine perfusion.

In comparison to livers with high bile output, livers in the low bile output group displayed more signs of hepatic necrosis (panels A and B) and venous congestion (panels C en D). Despite these differences in hepatic parenchymal damage between the two groups, there were no major differences in the degree of biliary damage (panels E and F).