Stretching the boundaries for liver transplant in the 21st century.

Given the high waiting list mortality, there is a clear need to identify strategies to increase the number of livers for transplantation. Some strategies require policy changes, whereas others depend on a better understanding of available opportunities. We divided the strategies to increase the number of livers for transplantation into two categories-those aiming to increase the use of organs considered to be of suboptimal quality, and those aiming to increase the use of organs considered to be of suboptimal size. Enough evidence suggests that, if considered in the context of other donor and recipient variables, grafts from elderly donors are a safe option. The severity of steatosis, and not simply its presence, is an important factor in contemplating the utility of steatotic grafts. Use of organs that have steatosis together with other factors that define extended-criteria organs should be avoided, particularly prolonged cold ischaemia time. Donation after circulatory death has an important role in increasing the donor pool, given the wide availability of organs from donors with this cause of death. This type of donation is hampered by a higher risk of ischaemia-reperfusion injury than other types of donation, which can result in graft complications and potential graft loss. Different types of machine perfusion have the potential to overcome these issues, and further research is needed to establish the best techniques and most cost-effective models. Despite the scarcity of data, the availability of safe and highly effective antiviral therapies means that the use of donors infected with hepatitis C virus (HCV) in recipients who are HCV negative can be considered as a strategy to increase the donor pool. Although data on transplantations using livers from living donors in patients with a Model for End-Stage Liver Disease (MELD) score higher than 20-24 are scarce, outcomes are similar to those achieved in patients with lower MELD scores, at least in reference centres. Increased use of split livers is an option if donors and recipients are carefully selected.