Split liver transplantation (SLT) was developed in the late 1980s to increase the number of donor graft livers used for liver transplantation (LT) [1]. However, the early outcomes of SLT were unfavorable [2]. The European Liver Transplant Registry reported that 3.7% of deceased donor liver transplantation (DDLT) operations between 1968 and 2000 were SLT, and this proportion increased to 6% during the 2000s [3,4]. In the United States, however, SLT accounted for less than 1% of all the LT cases performed between 2002 and 2009 [5]. Of the 2,462 patients who underwent DDLT in Korea from 2005 to 2014, 86 (3.5%) adult patients received split extended right liver (ERL) grafts [6]. Considering that a small number of deceased donor liver splitting was performed for two adults [7], the proportion of adult recipients undergoing SLT in Korea was estimated to be approximately 4%.

In conventional SLT, the deceased donor liver is divided into two parts, the left lateral section (LLS) graft for pediatric recipients and the ERL graft for adult recipients. Most SLTs are conventional and this has shortened the waiting list for pediatric LT candidates [8-11]. Because of the small case number of SLT, the outcomes of SLT are not well known yet. In this review, we aimed to review the Korean experience of SLT for one adult and one pediatric recipient to delineate the characteristics of conventional SLT in Korea.

Deceased donors are selected for SLT if they had stable hemodynamics, were aged ≤40 years, had a body weight ≥50 kg, and were being treated with low-dose inotropics [6]. The Korean Network for Organ Sharing (KONOS) policy requires donor organ splitting only for a combination of adult and child recipients. That is, if a candidate deceased donor fulfills the criteria for SLT, the KONOS selects appropriate adult and child recipients on the waiting list. If no proper candidates are available, then the whole liver graft is assigned to an adult recipient. If the whole liver graft appears to be too large for the single selected adult recipient, it can be utilized for two-adult SLT, to match the graft size and to expand the donor graft pool [7].

The detailed surgical techniques for adult-child SLTs have been previously described [7,12,13]. The usual LLS graft is actually an extended LLS graft, thus the left medial section parenchyma which is attached to the right liver does not function because all inflow vessels and bile duct are totally transected. The concept of right trisection grafts have therefore been replaced by ERL grafts [14,15]. The LLS graft after in situ splitting was often procured in advance, similar to the protocol for pediatric living donor liver transplantation (LDLT). Thereafter, the remnant ERL graft was harvested along with other abdominal organs.

From the first case of SLT in Korea on November 4, 1998 [16], 8 patients underwent SLT. Three adult patients received ERL graft and five pediatric patients received LLS graft. The livers were split following the in-situ method. At the time of writing, all the adult patients were still alive. One adult patient developed hepatic artery thrombosis one month following the SLT and underwent retransplantation due to graft failure. Another patient developed biliary leakage and had to undergo operative bile duct revision. Two pediatric patients passed on as a result of pneumonia and hepatic failure caused by hepatitis B virus, respectively. One pediatric patient suffered from hepatic venous stricture and persistent ascites and received interventional therapy. Overall, 3-year patient survival rate was 87.5% and graft survival rate was 75.0%. No primary non-function developed. Three patients (37.5%) suffered from vascular or biliary complications. It was concluded that the results of SLT were similar to conventional DDLT. Although SLT is technically difficult and increases the risk of vascular or biliary complications like LDLT, its outcome might be acceptable. Moreover, SLT could be regarded as a successful method to expand the donor pool if it would be performed in centers having experience in conducting LDLT [10].

Among the 2,462 patients who underwent DDLT from 2005 to 2014, authors retrospectively reviewed 86 (3.5%) adult patients who received an ERL graft. The outcomes of the ERL group were compared with those of 303 recipients who received whole liver transplantation (WLT). The recipient’s age, model for end-stage liver disease (MELD) score, ischemia time, and donor-to-recipient weight ratio (DRWR) between the two groups were similar (p>0.05). However, malignancy was uncommon (4.7% vs. 36.3%), and the donor was younger (25.2 years vs. 42.7 years) in the ERL group than in the WLT group (p<0.05). The technical complication rates and the 5-year graft survival rates (89.0% vs. 92.8%) were similar between the two groups (p>0.05). The 5-year overall survival rate (63.1%) and graft-failure-free survival rate (63.1%) of the ERL group were inferior than the WLT group (79.3% and 79.3%; p<0.05). The factors affecting graft survival rates were not definite. However, the factors affecting overall survival in the ERL group were MELD score >30 and DRWR ≤1.0. In the subgroup analysis, the overall survival between two groups was similar, if the DRWR was >1.0, regardless of the MELD score (p>0.05). It was concluded that a sufficient volume of the graft estimated from DRWR-matching could lead to better outcomes of adult SLTs with an ERL graft, even in patients with high MELD scores [6].

Between June 2016 and November 2019, 242 adult patients underwent a total of 256 DDLT operations. SLT was performed in 7 adult patients (2.9%). The mean age of SLT donors was 29.7±7.4 years, and the mean age of recipients was 55.7±10.6 years, with the latter having a mean MELD score of 34.6±3.1. Mean split ERL graft weight was 1,228.6±149.7 g and mean graft-to-recipient weight ratio (GRWR) was 1.97±0.39. Of the seven SLT recipients, the KONOS status was one in status 1, one in status 2 and five in status 3. The graft (p=0.72) and patient (p=0.84) survival rates were comparable in the SLT and WLT groups. Following propensity score matching, graft (p=0.61) and patient (p=0.91) survival rates remained comparable in the two groups. Univariate analysis showed that pretransplant ventilator support and renal replacement therapy were significantly associated with patient survival, whereas KONOS status category and diagnosis of primary liver diseases were not. Multivariate analysis showed that pretransplant ventilator support was an independent risk factor for patient survival. Authors concluded that survival outcomes were similar in adult SLT and WLT recipients, probably due to selection of high-quality grafts and low-risk recipients. Prudent selection of donors and adult recipients for SLT may expand the liver graft pool for pediatric patients without affecting outcomes in adults undergoing SLT [17].

Authors reviewed the data of Korean patients aged <18 years who received SLT from 2005 to 2014, based on the Korea national database and compared these data with recipients who underwent LDLTs at Seoul National University Hospital during the same period. A total of 63 and 56 patients were included in SLT and LDLT, respectively. The most common indication for LT was biliary atresia (60.3% in SLT vs. 67.9% in LDLT). The pediatric end-stage liver disease score did not differ between the groups (p>0.05). The 1-, 3-, and 5-year overall survival rates were 92.1%, 90.2%, and 86.6%, respectively, in the SLT group and 96.4%, 94.6%, and 94.6%, respectively, in the LDLT group (p=0.21); the corresponding graft survival rates were 88.9%, 87.1%, and 83.6%, respectively, in the SLT group and 92.9%, 91.0%, and 91.0%, respectively, in the LDLT group (p=0.31). Fulminant hepatic failure was a risk factor for graft failure (odds ratio=8.77 [range, 1.08–70.92]; p=0.042), but not overall survival (odds ratio=11.78 [range, 0.56–247.29]; p=0.11). It was concluded that the graft and overall survival rates of SLT and LDLT were not different in pediatric patients in Korea and that fulminant hepatic failure was the only risk factor affecting graft survival outcomes [18].

In Korea, the first child-adult SLT was performed in 1998 and the first two-adults SLT in 2003 [13,16]. Since then, the number and proportion of SLTs have increased, although both remain relatively small to date. There are two major reasons for the increase of SLT in Korea. The first is the increase in the number of deceased donors, thus increasing the number of donor candidates for SLT [19]. However, this increase has not been maintained in recent years, due to various medico-social issues [20,21]. The second reason is the changes in the KONOS SLT policy. Until 2012, a child recipient candidate for SLT was listed as a candidate for SLT only when the parents were unsuitable liver donors [20]. Since 2013, all pediatric candidates for DDLT were considered eligible for SLT [6].

The annual number of pediatric LTs is less than 70 in Korea. In contrast, the proportion of pediatric DDLTs increased to 50% in 2014. The increase in the number of deceased donors correlated with the increase in the number of SLTs. Possible reasons for the increase in number of DDLTs between 2011 and 2013 were described in a Korean adult SLT study [6]. In 2010, an independent Korean organ procurement organization was established by the government. Since 2011, reporting potentially brain-dead candidates to this organization has been a legal obligation of medical staff who were the primary caregivers of these patients. Another reason is the changes in the surgical policy in 2013 to expand the donor organ pool for SLT [6]. If the outcomes of SLT are similar to those of LDLT, the increased number of SLTs could support the substitution of LDLT. A Korean multi-center study presented that the graft and overall survival rates of SLT and LDLT were not significantly different in pediatric patients in Korea and that fulminant hepatic failure was the only risk factor affecting graft survival outcomes [18].

The major concern of transplant surgeons regarding adult SLT recipients is that the outcomes of ERL-SLT would be similar to those of WLT. The graft liver remaining after removal of the LLS is functionally comparable to an ERL graft [14,22]. Thus, the reserved capacity of the graft function would be reduced according to the remaining size of the right liver mass, thus being a marginal liver graft. Implantation of such a marginal liver graft to a high-risk patient might worsen post-transplant outcomes. A Korean multicenter study found that the risk factors for patient survival of SLT recipients were GRWR ≤1.0% and MELD score >30 [6]. Because deceased donor grafts are subject to preservation and reperfusion injuries, a GRWR ≥1.0% is highly recommended for adult SLT recipients [7,17]. Because many adult DDLT candidates are currently in very poor condition with very high MELD scores, and because the number of deceased donor livers has not increased, many critically ill patients received marginal liver grafts. The deceased donor livers selected for SLT were of high quality, resulting in a low risk of severe early graft dysfunction or primary non-function. The candidates for adult SLT were carefully selected. Combination of these two factors suggested that the outcomes of adult SLT would be comparable to those of LDLT using ERL grafts [17].

In conclusion, this collective review demonstrated that survival outcomes were comparable between adult SLT and WLT recipients as well as between pediatric SLT and LDLT. Careful selection of donors and adult recipients for SLT might expand the liver graft pool for pediatric patients without affecting the outcomes of adult recipients undergoing SLT.

There was no funding related to this study.

All authors have no conflicts of interest to declare.

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