Split liver transplantation (SLT) for two adult patients (SLT2A) is a procedure that a deceased donor whole liver is split into two hemi-liver grafts for two patients [1,2]. Since one liver graft can be shared between two adult recipients, SLT2A increases the number of available grafts and reduces the waitlist time and mortality [3-5]. This technique might especially favor smaller adolescents and adult patients who are disadvantaged on the waiting list to receive a timely size-matched graft [6-8]. The world-first case of SLT2A was reported in 1989 [1]. The first case of SLT2A in Korea was performed in 2003. Numerous cases of adult living donor liver transplantation (LDLT) have been performed during the last 25 years in Korea. Considering that the principles and techniques of liver splitting are similar between adult LDLT and SLT2A, the large experience of LDLT has greatly influenced the development of SLT2A in Korea. Therefore, we aimed to review Korean experience of SLT2A to delineate the characteristics of SLT2A in Korea.

A brain-dead donor was a 22-year-old man weighing 65 kg. His liver volume was estimated to be 2,120 mL on computed tomographic volumetry. As it seemed to be too large for a 60 kg recipient candidate, SLT was planned after assessing hemi-liver volume and middle hepatic vein (MHV) anatomy. The right lobe was mobilized first and the liver parenchyma transected along the right border of the MHV. A 1,240 g-weighing right lobe (segments V–VIII) graft was implanted into a 57-year-old male patient with acute-on-chronic liver failure in the same manner as a living donor liver graft. After that, routine procedures of deceased donor multi-organ procurement were performed. A 670 g-weighing left lobe (segments I–IV) with retrohepatic vena cava, common bile duct, and aortic patch was implanted into another 37-year-old male recipient. These two recipients recovered uneventfully, surviving 12 months to the date of writing. Authors integrated the techniques learned from hundreds of cases of adult LDLTs into this first case of SLT2A [9].

From 2003 to 2014, authors had performed 16 cases of adult SLT2A from eight deceased donors using in situ splitting technique. Authors investigated results of SLT2A and compared the outcomes of SLT2A with those of 393 cases of primary whole liver transplantation (WLT). All SLT donors were males. Eight recipients received a right liver graft. Seven recipients received a left liver graft. One recipient received a dual-donor liver transplantation with two left liver grafts (one from a split deceased donor liver and one left liver graft from a living donor). The mean age of recipients was 49.6±7.0 years. The model for end-stage liver disease (MELD) score of recipients was 21.3±8.6. The mean cold ischemic time was 345.6±311.7 minutes. Graft and patient survival rates were 75.0% and 81.3%, respectively, at both 1 year and 5 years. There were two cases of biliary complication and three cases of vascular complication. However, there was no incidence of arterial complication or small-for-size graft syndrome. The donor age of the SLT2A group was younger than that of the WLT group. The MELD score of the SLT2A group was lower than that of the WLT group. Patient and graft survival rates did not differ significantly between SLT2A and WLT groups. Authors concluded that in situ SLT2A is a feasible option to expand door pools in selected situations [10].

Four deceased marginal donor split liver procedures have been performed for eight adult recipients since 2017. Three liver splits were made in situ and one split procedure was carried out ex situ. Three of four donors had elevated aspartate transaminase and alanine transaminase levels beyond three times of the reference values. One of them was 60 years old. After splitting the liver, all four right grafts were allocated to patients having high-MELD score and left grafts with main vascular structures were transplanted to sub-urgent waiting list individuals. Graft-to-recipient body weight ratio ranges for right and left liver grafts were 1.5 to 2.2 and 0.9 to 1.4, respectively. Cold ischemic time ranged from 59 to 388 minutes. Graft liver function of all recipients recovered without remarkable events. One recipient of the right liver graft died at 11 months after transplantation due to aggravating preexisting myelofibrosis. One left liver recipient for liver re-transplantation after primary liver graft failure expired due to cerebral infarct on post-transplantation 21 days. Authors concluded that SLT2A from selected deceased marginal donor grafts to both adult recipients has the potential to expand donor pool [11].

The technique of splitting a deceased donor liver to be used for two adults is a unique method to increase the number of liver grafts and to decrease waiting list mortality. However, SLT2A has remained challenging because it is associated with relatively poor outcomes [10-13], suboptimal graft condition, and technical difficulty [14,15].

SLT2A has been performed in some highly selected situations. Proper donor selection is the first step for successful SLT2A. From the viewpoint of selecting deceased donors, the criteria for SLT2A include young age, low body mass index, stable hemodynamic status with minimal inotropic agent, normal liver function, and short period of hospitalization before donation [12-17]. Appropriate selection of recipients is essential to maintain outcomes of SLT2A. In Korea, SLT2A has become more difficult after the adoption of MELD-based organ allocation system or "sickest first" allocation system because at least one of the two hemi-liver grafts should be engrafted into a recipient with a very high-MELD score. Under the MELD score-based allocation system, splitting of the liver graft that has been allocated as the whole graft to urgent recipients with high-MELD score gives rise to some ethical questions [10]. A large-for-size graft allocated to recipients requiring urgent liver transplantation might be most suitable for SLT2A under the MELD score-based allocation.

There are two methods to split the donor liver, in situ and ex situ techniques. The in situ technique can decrease cold ischemic time by removing the graft division procedure during bench work, lower the risk of bile leak, and facilitate complete hemostasis of liver cut surface. However, the in situ technique is time-consuming. It requires cooperation with other organ harvesting teams. In addition, it may increase blood loss [10]. A meta-analysis of right-liver SLT versus WLT in adult recipients has shown that the incidence of biliary complications is increased after ex situ SLT, but not after in situ SLT [18].

Surgical techniques for right and left hemi-liver grafts in deceased donors are similar to those for donor hepatectomy used in LDLT. There are several technical options to split a deceased donor liver into two right- and left hemi-liver grafts according to the allocation of the segment I, including the main portal vein trunk, common bile duct, celiac trunk, MHV, and retrohepatic inferior vena cava. It is generally accepted that splitting the liver into segments V–VIII without the MHV trunk as a right hemi-liver graft and segments I–IV with the MHV trunk as a left hemi-liver graft is more suitable for two adult recipients. A right hemi-liver graft without MHV trunk might cause severe hepatic venous congestion as shown in the experience of LDLT [19]. However, there are several effective reconstruction methods for MHV tributaries to prevent such hepatic venous congestion at the anterior section in the LDLT setting [20,21]. A right hemi-liver graft with multiple and complex inferior right hepatic veins drained into the vena cava can also be securely reconstructed using the techniques developed for LDLT [22,23].

Several studies have reported that the incidence of major complications of grade III or higher in SLT recipients ranges from 38% to 72% [12,17,24]. Common complications following SLT2A include biliary complications (including bile leak and biliary stricture), vascular complications (including hepatic artery, portal vein, and hepatic vein thrombus), bleeding requiring intervention or exploratory laparotomy, infection, primary non-function, and small-for-size syndrome [13,15-17,24,25]. Among these, biliary and vascular complications were the most frequent. A collective review on outcomes of SLT2A has been performed [12]. When outcomes of SLT2A were compared with those of WLT and LDLT, there were no significant differences in several single-center studies [10,14,24,26], although SLT2A revealed poorer outcomes than WLT in a multicenter study [17].

In Korea, the number of SLT2A is still very small because there are only selection criteria of SLT for one adult and one pediatric recipient in the current Korean Network for Organ Sharing (KONOS) setting. Selection criteria for SLT2A are currently unavailable. Thus, it is necessary to establish organ allocation polices to encourage widespread application of SLT2A. If a whole liver graft for one recipient is allocated to a certain hospital and SLT2A is then attempted, it is reasonable to make the hospital have a priority to get all grafts independent of the MELD score [10].

In conclusion, SLT2A is a feasible option to expand door pools in selected situations of deceased donor liver transplantation in the current setting in Korea.

There was no funding related to this study.

All authors have no conflicts of interest to declare.

Conceptualization: JIP. Data curation: All. Formal analysis: All. Investigation: All. Methodology: All. Writing – original draft: All. Writing – review & editing: All.