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Policy and Practice Impacts on Liver Exchange

How Liver Exchange Differs from Kidney Exchange?

While our original formulation of kidney exchange in Roth, Sönmez and Ünver (2004) included compatible patient-donor pairs, practical implementation of our policy recommendations in real-life kidney exchange clearinghouses has largely been restricted to incompatible pairs. Since blood-type compatibility is a prerequisite for kidney transplantation in most transplant centers, this restriction has been resulting in significant efficiency loss. As an illustration, in contrast to a blood-type O patient with a blood-type A donor who have a natural inclination to join a kidney exchange pool, a blood-type A patient with a blood-type O donor rarely joins to a kidney exchange pool (typically only when they are tissue-type incompatible).  Hence, under current practices, a vast majority of blood-type O patients with non-O donors cannot benefit from kidney exchange. The key challenge here is the lack of a “biological” incentive mechanism for living-donor kidney transplantation which compels compatible pairs to join a kidney exchange pool. (See Sönmez, Ünver and Yenmez (2020) for an “institutional” incentive mechanism.)

This observation is the basis of one of the important differences between liver exchange and kidney exchange. Unlike a living-donor kidney transplantation in which a whole kidney is transplanted, only part of a liver (the right lobe, the left lobe, or segments 2-3 of the left lobe) is transplanted in a living-donor liver transplantation. For patient safety, the norm is to assure that the patient is transplanted a liver graft which has at least 40% of the volume of the patient’s dysfunctional liver. Since the right lobe is the larger of the two lobes with 60-70% of the volume of the liver, it is typically the only viable transplant option for most patients who have blood-type compatible living donors. However, donor mortality and donor morbidity are both 3 to 5 times higher for right-lobe donation than for left-lobe donation. Hence, this substantial difference in donor risk creates a “biological” incentive mechanism for a significant fraction of compatible patient-donor pairs to join a liver exchange pool: Through a donor exchange with another pair with a relatively smaller patient, the donor may be able to secure a transplant for her co-registered patient by donating her much less risky left lobe (or segments 2-3 of the left lobe) rather than her higher-risk right lobe. Building on this inherent biological incentive, in Ergin, Sönmez and Ünver (2020) we both introduce an additional ethical argument in favor of liver exchange and also formulate an efficient and incentive compatible liver exchange mechanism.

Banu Bedestenci Sönmez Liver Exchange System

Building on these ideas in Ergin, Sönmez and Ünver (2020), together with Utku Ünver, we reached an agreement with the leadership of the liver transplant institute at Inonu University (Malatya-Turkey) in September 2019 to set up and run a single-center liver exchange system. Only next to the ASAN Medical Center in Seoul-South Korea, the institute at Inonu University is the second highest-volume liver transplant center worldwide with 250-300 living-donor liver transplants annually. As part of our agreement, the system was named after my beloved late wife Banu Bedestenci Sönmez whom we lost in August 2016. After three years of a delay due to bureaucracy and the Covid-19 pandemic, Banu Bedestenci Sönmez Liver Exchange System was launched in June 2022.

International Media

The First 4-Way Liver Exchange in the World

At the leadership of Prof. Dr. Sezai Yilmaz, the liver institute at Inonu University has the capacity to carry out up to seven simultaneous liver transplants. In 2022, twelve patients received liver transplants through the system in four 2-way exchanges and one 4-way exchange. The initial results of the Banu Bedestenci Sönmez Liver Exchange System along with its operational principles and ethical framework are reported in Yilmaz et al. (2023).

The 4-way exchange performed in July 2022 was a first worldwide. Since then two additional 4-way exchanges are carried out by the system. These three 4-way exchanges are the largest liver exchanges carried out worldwide as of September 2023. In addition, five of the seven 3-way exchanges carried out and documented worldwide are are also carried out under the system.

In total, 43 patients received liver transplants through the Banu Bedestenci Sönmez Liver Exchange System as of  9/27/2023 in

• eight 2-way,

• five 3-way, and

• three 4-way exchanges.