Ex situ normothermic machine perfusion (NMP) is increasingly used for viability assessment of high‐risk donor livers, whereas dual hypothermic oxygenated machine perfusion (DHOPE) reduces ischemia‐reperfusion injury. We aimed to resuscitate and test the viability of initially‐discarded, high‐risk donor livers using sequential DHOPE and NMP with two different oxygen carriers: an artificial hemoglobin‐based oxygen carrier (HBOC) or red blood cells (RBC). In a prospective observational cohort study of 54 livers that underwent DHOPE‐NMP, the first 18 procedures were performed with a HBOC‐based perfusion solution and the subsequent 36 procedures were performed with an RBC‐based perfusion solution for the NMP phase. All but one livers were derived from extended criteria donation after circulatory death donors, with a median donor risk index of 2.84 (IQR 2.52–3.11). After functional assessment during NMP, 34 livers (63% utilization), met the viability criteria and were transplanted. One‐year graft and patient survival were 94% and 100%, respectively. Post‐transplant cholangiopathy occurred in 1 patient (3%). There were no significant differences in utilization rate and post‐transplant outcomes between the HBOC and RBC group. Ex situ machine perfusion using sequential DHOPE‐NMP for resuscitation and viability assessment of high‐risk donor livers results in excellent transplant outcomes, irrespective of the oxygen carrier used.

Static cold storage Extended hypotermic oxygenated machine perfusion enables ex situ preservation of porcine livers for up to 24 h Dynamic preservation with DHOPE Reperfusion and viability assessment 2 h SCS 2 h DHOPE 4 h reperfusion 2 h SCS 6 h DHOPE 4 h reperfusion 2 h SCS 24 h DHOPE 4 h reperfusion 8-11 h SCS 20 h DHOPE 3 h reperfusion 24 h SCS 4 h reperfusion Decreasing venous and arterial flows, no bile production, injured appearence Non-viable livers • Lactate clearance, blood pH, glucose, ALT • Biliary pH, bicarbonate, LDH • HMGB-1, IL-6, TNFα, cfDNA • Bile duct and liver parenchyma histology Viable livers, all with similar: Lactate <1.7 mmol/L, perfusate pH7.35-7.45, bile production >10 ml, biliary pH >7.45 Livers meet viability criteria during 2.5 h Highlights DHOPE can be extended for up to 24 h to prolong donor liver preservation time. Hepatocellular and biliary function is maintained after ex situ preservation by 24 h DHOPE. Extension of DHOPE for up to 24 h does not induce more injury compared to shorter preservation times. The initial results of extended preservation by DHOPE for discarded human livers are promising. Lay summary It has been suggested that preserving liver grafts with a technique called (dual) hypothermic oxygenated machine perfusion ([D]HOPE) leads to better outcomes after transplantation than if livers are stored on ice, especially if an organ is of lesser quality. In this study, we showed that DHOPE could be used to preserve liver grafts for up to 24 h. This extended procedure could be used globally to facilitate transplantation and expand the donor pool.

The transplant community continues to be challenged by the disparity between the need for liver transplantation and the shortage of suitable donor organs. At the same time, the number of unused donor livers continues to increase, most likely attributed to the worsening quality of these organs. To date, there is no reliable marker of liver graft viability that can predict good posttransplant outcomes. Ex situ machine perfusion offers additional data to assess the viability of donor livers before transplantation. Hence, livers initially considered unsuitable for transplantation can be assessed during machine perfusion in terms of appearance and consistency, hemodynamics, and metabolic and excretory function. In addition, postoperative complications such as primary nonfunction or posttransplant cholangiopathy may be predicted and avoided. A variety of viability criteria have been used in machine perfusion, and to date there is no widely accepted composition of criteria for clinical use. This review discusses potential viability markers for hepatobiliary function during machine perfusion, describes current limitations, and provides future recommendations for the use of viability criteria in clinical liver transplantation.