Machine perfusion of the liver: Putting the puzzle pieces together

Table 2 Parameters employed in clinical studies to assess the viability of donor organs before transplantation

Ref.	Method	Perfusate parameters	Bile parameters	Perfusion parameters
Watson et al[11]	NRP	Within 2 h of NRP: Alanine transaminase up to 500 IU/L, providing no continued rise between the first and second hours
Muller et al[34]	HMP	At least 1 h of HMP: Threshold at 10000 A.U. (100 ng FMN/mL perfusate) to refuse livers regardless of the use of a DCD or DBD liver
Watson et al[32]	NMP	No timepoint defined: Changes in lactate, glucose, and transaminase concentrations and the ability of the liver to maintain perfusate pH without supplemental bicarbonate
Matton et al[26]	NMP		Within 2.5 h of NMP: Bicarbonate concentration > 18 mmol/L, pH > 7.48, glucose concentration < 16 mmol/L, bile/perfusate glucose concentration ratio < 0.67, and LDH concentration < 3689 U/L
de Vries et al[14]	NMP	Within 150 min of NMP: Lactate concentration within “normal” values (0.5-1.7 mmol/L); pH within normal values (7.35-7.45), without continuing sodium bicarbonate supplementation	Within 150 min of NMP: Cumulative bile production of ≥ 10 mL and ≥ 4 mL in the preceding hour. pH > 7.45
Mergental et al[6]	NMP	Within 4 h of NMP: Lactate ≤ 2.5 mmol/L; and two or more parameters: pH ≥ 7.30; Evidence of glucose metabolism	Within 4 h of NMP: Evidence of bile production	Within 4 h of NMP: HA flow ≥ 150 mL/min and PV flow ≥ 500 mL/min; and homogenous perfusion of the parenchyma
Cardini et al[50]	NMP	Within 2 h of NMP: Rapid decrease and maintenance of lactate to physiological levels, maintenance of physiological pH values without sodium bicarbonate supplementation, and glucose consumption. Remarkably high transaminases and LDH levels and a severe rise of these parameters are deemed warning signals	Within 2 h of NMP: Bile production and bile pH are indicators for bile duct viability and function
Reiling et al[51]	NMP	Within 2 h of NMP: Lactate clearance to < 2 mmol/L. Within 4 h of NMP: Evidence of glucose metabolism. Maintenance of physiological pH without continuing administration of sodium bicarbonate	Within 4 h of NMP: Bile production (no lower limit)	Within 4 h of NMP: Stable hepatic arterial and portal venous flows. Homogeneous graft perfusion with soft consistency of parenchyma

DCD: Donation after circulatory death; DBD: Donation after brain death; HA: Hepatic artery; HMP: Hypothermic machine perfusion; LDH: Lactate dehydrogenase; NMP: Normothermic machine perfusion; NRP: Normothermic regional perfusion; PV: Portal vein.