Donor liver weight in normothermic machine perfusion: Does size really matter?

BACKGROUND: Large livers undergoing normothermic machine perfusion are believed to demonstrate altered homeostasis and heterogeneous graft perfusion during normothermic machine perfusion; these features of large livers may dissuade their use for normothermic machine perfusion and transplantation, reducing the donor pool. However, it remains unclear if liver size has an impact on transplant outcomes following normothermic machine perfusion. METHODS: A retrospective, single-center review of all transplanted livers that underwent normothermic machine perfusion (OrganOx metra) over a 32-month period was conducted. Livers were categorized by weight into 3 equal tertiles: small (<1,570 g), medium (1,570-1,870 g), and large (>1,870 g). Perfusate lab metrics during normothermic machine perfusion and recipient outcomes were analyzed. RESULTS: During the study period, 151 livers underwent normothermic machine perfusion with subsequent transplantation, with 50, 51, and 50 livers in small, medium, and large weight groups, respectively. During normothermic machine perfusion, the perfusate of large livers had significantly higher transaminase levels than the perfusate of medium and small livers, on average, over time. Perfusate glucose, pH, and lactate levels were similar across weight groups. There was a trend toward elevated post-transplant transaminases (P = .026) with increasing liver weight. Large liver recipients had no increase in 90-day mortality or graft failure, 30- or 90-day readmission, intensive care unit/hospital length of stay, or vascular/biliary complications. In multivariable analysis, large liver size was independently associated with cradle compression; cradle compression was independently associated with early allograft dysfunction. CONCLUSIONS: Use of normothermic machine perfusion for large livers results in similar clinical outcomes compared with smaller allografts despite higher on-pump and post-transplant transaminase release. These findings suggest that size-universal normothermic machine perfusion viability criteria can be used for large livers to safely expand the pool of eligible donor organs.