Viability Assessment During Normothermic Machine Liver Perfusion: A Literature Review

Abstract

The discrepancy between donor organ availability and demand leads to a significant waiting-list dropout rate and mortality. Although quantitative tools such as the Donor Risk Index (DRI) help assess organ suitability, many potentially viable organs are still discarded due to the lack of universally accepted markers to predict post-transplant outcomes. Normothermic machine perfusion (NMP) offers a platform to assess viability before transplantation. Thus, livers considered unsuitable for transplantation based on the DRI can be evaluated and potentially transplanted. During NMP, various viability criteria have been proposed. These criteria are neither homogeneous nor consensual. In this review, we aimed to describe the viability criteria during NMP and evaluate their ability to predict hepatic graft function following transplantation. We conducted a PubMed search using the terms 'liver transplantation', 'normothermic machine perfusion' and 'assessment', including only English publications up to February 2024. Viability assessment during NMP includes multiple hepatocellular and cholangiocellular criteria. Lactate clearance and bile production are commonly used indicators, but their ability to predict post-transplant outcomes varies significantly. The predictive value of cholangiocellular criteria such as bile pH, bicarbonate and glucose levels remains under investigation. Novel markers, such as microRNAs and proteomic profiles, offer the potential to enhance graft evaluation accuracy and provide insights into the molecular mechanisms underlying liver viability. Combining perfusion parameters with biomarkers may improve the prediction of long-term graft survival. Future research should focus on standardising viability assessment protocols and exploring real-time biomarker evaluations, which could enhance transplantation outcomes and expand the donor pool.

Keywords: liver transplantation; normothermic machine perfusion; viability assessment.

FIGURE 1

Perfusate and bile characteristics of viable livers during NMP. The dotted lines represent cutoff values used as viability criteria in clinical studies. Figures are based on the studies listed in Table 1, adapted from Brüggenwirth [18] et al. and Watson et al. [29]. (A) perfusate lactate, (B) bile production, (C) perfusate glucose, (D) perfusate pH, (E) HA flow, (F) PV flow, (G) transaminases in perfusate, (H) bile pH, (I) Δ pH, (J) Δ bicarbonates, (K) Δ Glucose.