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Policy and Practice Impacts on Liver Exchange

Banu Bedestenci Sönmez Liver Exchange System

Background: 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

Expanding upon the ideas presented in Ergin, Sönmez and Ünver (2020) and further enhancing them, Utku Ünver and I reached an agreement with the leadership of the liver transplant institute at Inonu University (Malatya, Turkey) in September 2019 to establish and operate a single-center liver exchange system. Our collaboration revealed that, once again, because of size compatibility requirements for liver exchange, there are also other, and likely more significant, “biological” incentives for blood-type compatible pairs to participate in liver exchange. For instance, the anatomical structures of the left lobes of many prospective donors are often unsuitable, while pediatric patients invariably require a transplant that involves all or part of the left lobe. The presence of size incompatibility requirements has offered us several such avenues to encourage the inclusion of blood-type compatible pairs in the system.

The Liver Transplantation Institute at Inonu University, located in Malatya, Turkey, is the second-highest-volume liver transplant center worldwide, performing 250-280 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 a three-year delay caused by bureaucracy and the Covid-19 pandemic, the pilot phase of the Banu Bedestenci Sönmez Liver Exchange System was launched in June 2022.

The First 4-Way Liver Exchange in the World

Under the leadership of Prof. Dr. Sezai Yilmaz, the liver institute at Inonu University has the capacity to perform up to six simultaneous liver transplants within the institute and up to eight simultaneous liver transplants within the hospital. 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 and the largest liver exchange reported in the academic literature or media. Since then, the system has carried out six additional 4-way exchanges.

Increased Performance of the System after its Pilot Phase

The First 5-Way Liver Exchange in the World 

As of  October 5, 2024, a total of 167 patients received liver transplants facilitated by the Banu Bedestenci Sönmez Liver Exchange System  in

• two 7-way,

• four 6-way,

• three 5-way,

• seven 4-way,

• fourteen 3-way, and 

• twenty-two 2-way exchanges.
  

Out of the 167 transplants, 15 were performed during the initial 14-month pilot phase, and 152 were conducted after the system was publicly announced on July 28th, 2023.

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