Liver exchange has a lot in common with kidney exchange, in the sense that the issues involved in forming cycles and chains once you know which donors are compatible with which patients are very similar. But a big difference is what constitutes a compatible donor: for livers, size (of the donor, and the donor liver) is very important, sensitively so.
Here's a paper forthcoming in the American Journal of Transplantation, by a team of transplant physicians and economists (with kidney exchange experience), on the importance of size.
"Enhanced Role of Multi-Pair Donor Swaps in Response to Size Incompatibility: The First Two 5-Way and the First 6-Way Liver Paired Exchanges" by Sezai Yilmaz, MD, FACS, Tayfun Sönmez, PhD, M. Utku Ünver, PhD, Volkan Ince, MD, Sami Akbulut, MD, PhD, FACS, Kemal Baris Sarici, MD, and Burak Isik, MD, American Journal of Transplantation, Brief communication, in press.
Abstract: A significant portion of liver transplantations in many countries is conducted via living-donor liver transplantation (LDLT). However, numerous potential donors are unable to donate to their intended recipients due to factors such as blood-type incompatibility or size incompatibility. Despite this, an incompatible donor for one recipient may still be a viable donor for another patient. In recent decades, several transplant centers have introduced liver paired exchange (LPE) programs, facilitating donor exchanges between patients and their incompatible donors, thereby enabling compatible transplants. Initially, LPE programs in Asia primarily involved ABO-i pairs, resulting in 2-way exchanges mainly between blood-type A and B recipients and donors. This practice has led to a modest 1-2% increase in LDLTs at some centers. Incorporating size incompatibility alongside blood-type incompatibility further enhances the efficacy and significance of multiple-pair LPEs. Launched in July 2022, a single-center LPE program established at Inönü University Liver Transplant Institute in Malatya, Türkiye, has conducted thirteen 2-way, nine 3-way, four 4-way, two 5-way, and one 6-way LPEs until February 2024. In 2023 alone, this program facilitated 64 LDLTs, constituting 27.7% of the total 231 LDLTs performed. This paper presents the world's first two 5-way LPEs and the first 6-way LPE.
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Another (not entirely unrelated) domain in which size is important, and exchange involves many pairs, involves the exchange of shells among hermit crabs. See these earlier posts (which included this short video):
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