*Purpose: The VITTAL (viability testing and transplantation of marginal livers) clinical trial demonstrated that ex situ end-ischaemic normothermic machine perfusion (NMP) allows functional assessment and transplantation of a large proportion of currently unutilised high-risk donor livers. This study aims to assess whether achievement of the VITTAL criteria for transplantability during NMP correlates with hepatobiliary injury and post-transplant outcomes.

*Methods: The transplantability of discarded high-risk donor livers was assessed during 4 hours of NMP using predefined viability criteria, consisting of: perfusate lactate levels ≤2.5mmol/L, presence of bile production, perfusate pH >7.30, metabolism of glucose, stable vascular arterial flow ≥150mL/min and portal vein flow ≥500mL/min. The livers were supplied with taurocholic acid and the perfusion performed on the OrganOx Metra® device. Perfusate transaminases, bile production and bile properties were assessed and correlated with post-operative clinical complications including ischemic-type biliary lesions (ITBL), early-allograft dysfunction (EAD) and post-reperfusion syndrome (PRS).

*Results: Twenty-two out of thirty-one (71%) livers meet the criteria and were transplanted. Livers deemed non-transplantable during NMP exhibits higher release of transaminases in the perfusate, suggesting more severe hepatobiliary injury (peak ALT -median[Interquartile range]- 9,667[4,600-20,505]vs. 2,410[1,130-4,832]IU/L, p<0.001; peak AST 14,033[5,902-28,436]vs. 4,760[2,316-6,533]IU/L, p=0.001; peak GGT 142[66-527]vs. 118[82-174]IU/L, p=0.051). Although the perfusate transaminase levels do not distinguish cases of PRS, EAD or ITBL post-transplantation, the peak ALT correlates with the recipients’ peak ALT ([Spearman’s]r=0.445, p=0.063). Eight patients (36%) developed ITBL on imaging within 180-days post-transplantation. Whilst bile production does not correlate with ITBL, bile pH <7.85 differentiates patients that developed ITBL (AUROC=0.836[95%CI:0.568->0.999], Sensitivity=91%, Specificity=80%, p=0.036).

*Conclusions: Viability assessment of high-risk donor livers during NMP using the VITTAL criteria might prevent transplantation of organs with severe hepatobiliary damage. Perfusate transaminases do not correlate with post-transplant complications. In the context of NMP with taurocholic acid supplementation, the bile pH cut-off of 7.85 may differentiates livers that develop ITBL following transplantation.

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