Split liver transplantation and allocation policy: An uncertain connection

Split liver transplantation (SLT), in which a liver is divided for 2 recipients, was developed in the 1980s,1 advanced in the 1990s,2 but has remained a niche activity in the field today. The procedure is technically and logistically demanding and primarily the purview of teams that perform both adult and pediatric transplants. There is substantial technical overlap with living donor liver transplantation (LDLT) but a very different team context—SLT depends on organ recovery and preservation, while LDLT has an extensive care system involving the donor.3 In this issue of Liver Transplantation, Nakayama et al4 attempt to link SLT activity with overall changes in allocation policy. They further observe varying relationships between SLT and LDLT activity in the high-volume split centers. The study considers 8 years of OPTN data, during which SLT accounted for only 1470 of nearly 60,000 transplants (2%). Between 2016 and 2023, the total number of deceased donors increased by 46% and the total number of liver transplants by 50%. In the middle of that era, allocation policy changed to increase the area of distribution to improve access for the sickest patients. The authors reasoned that when faced with an increased donor pool, the “best” livers (which are more able to be split, or “splittable”) might be more likely to be used as whole livers for the sickest patients, with MELD-Na scores ≥30. “Splittable” is defined by the OPTN as a donor under 40 years old, on no more than 1 vasopressor, serum transaminase ≤3 times upper limit of normal, and body mass index≤28.5 The rapid growth of OLT volumes predated the acuity circles allocation change and has continued, likely potentiated by the rapid growth of machine preservation, bringing many new donors into the pool, including increased use of DCD and other “marginal” livers that can now be tested and utilized successfully.6,7 Considerations in performing SLT primarily involve team priorities, especially focused on access to OLT for children and smaller adults. The splitting procedure requires an experienced surgeon at each time point, based on the recovery of a deceased donor meeting “ideal” characteristics, and the recipient surgery being longer and more difficult with an increased risk of technical complications. In many circumstances, a single center performs the splitting and the transplants for both recipients, ideally requiring 3 nearly concurrent operations, each led by an experienced surgeon. While the motivation is admirable, the price of effort is high, and only teams with the technical capability and the drive to increase access for children and small adults choose to make the extra effort. Nakayama and colleagues found that all the “high-volume” SLT centers performed both adult and pediatric transplants, defined as >4 cases yearly. Nakayama and colleagues hypothesized that the acuity circles would result in a change in access to “splittable” livers and thus expected to see a decline in SLT after the change. This was confirmed, though the decrease was modest, and by 2023, SLT activity had returned to baseline. However, since overall transplant activity had doubled, the rate of SLT is now half of what it was in 2016. The authors noted several other modest changes in SLT over the study period, concerning recipient types and the co-existing use of LDLT in some centers. Overall, the changes in SLT observed in the study are not convincingly attributed to allocation policy. The dominant story here is the doubling of the organ supply and liver transplant activity in the past 8 years. This is remarkable, and likely multifactorial, including regulatory pressure on donation and OPO performance, center performance expectations regarding access metrics and organ utilization, and continued training and development of increasingly capable transplant surgeons. With respect to SLT, changes in volume are largely attributable to the center priorities and capabilities of the individual teams. As noted by the authors, NMP would be expected to enable the use of splits by extending the preservation time and improving logistic challenges.8,9 It is unfortunate that the authors were not able to perform a detailed subset analysis of the center characteristics associated with SLT, as SLT and LDLT are limited by low numbers overall and arbitrary cutoffs to define high-volume centers. For such small numbers, changes in personnel, such as the recruitment of a surgeon with expertise in LDLT, might substantially alter the orientation of the team regarding SLT. Perhaps the most interesting consideration here is the definition of a splittable liver and the likelihood that this could contribute pressure to increase SLT. The authors suggest that up to 45.8% of livers are splittable in the post-acuity circle era, compared with 39.8% beforehand. However, if high MELD patients are prioritized for the highest quality grafts that would traditionally be suitable for split transplants, we could expect hesitancy to use a split graft with increased risk toward outcomes for a very sick patient (small-for-size, long cold ischemia times, and complex vascular reconstruction). In addition, we have long argued that the pediatric population is limited and can only drive 200–300 splits per year. This is further evidence that SLT is a highly idiosyncratic activity. It would be an interesting proposal to list the “intention to split” recipient pairs of small adults at the same center together to facilitate timely allocation when a split offer becomes available, but such intrusive policy changes have been difficult to implement.