How can we optimize the outcome of liver grafts from pediatric donors?

The outcome of pediatric liver donors, particularly those from small donors, transplanted into adult recipients has not been well studied. Yet, as the donor shortage escalates and the discrepancy between the number of adults as compared with children awaiting liver transplantation continues to widen,1,2 pediatric donors are increasingly more likely to be directed to adult recipients. Therefore, the analysis of risk and outcomes of this practice, reported by 2 large experienced liver programs in this issue of Liver Transplantation, is highly relevant to the ongoing debate of how the precious commodity of donor livers should be best utilized. Both Yasutomi et al from the Mayo Clinic and Emre et al from Mount Sinai Hospital focus on the 2 critical questions relevant to placing a small graft in a larger recipient: (1) Are there increased technical risks? (2) What is the physiologic effect of the mismatch between the relatively small hepatocyte mass of the graft and the size of the recipient? The 2 authors choose different comparative groups to study the effect of the small pediatric liver donor transplanted into the adult recipient. The Mayo study compares the outcome of small pediatric donors to larger pediatric donors (12 to 18 years of age), whereas the Mount Sinai study compares pediatric donors ,13 years of age to adult donors $19 years of age. However, because both authors define the small pediatric donor as #12 years of age, several important comparisons can be made. In both studies the incidence of hepatic artery complications was significantly increased when small pediatric liver donors were placed into adult recipients. In the Mayo clinic experience, the 1-year cumulative probability of vascular complications was 24% for small pediatric liver donors compared with 4.7% (P 5 .011) if the donor was 12 to 18 years old. Moreover, younger donor age was associated with a significant graft survival disadvantage at 1 year: 64.3% compared with 87.5% for liver donors ages 13 to 18 years. In the Mount Sinai experience, hepatic artery thrombosis was also significantly higher in the pediatric liver donor group compared with the adult donor group, 12.9% versus 3.8%, respectively, with a trend to decreased graft survival at 1 year in the pediatric donor group, 68.6% versus 75.0%. Interestingly, both centers found a relationship between cold ischemia time and hepatic artery thrombosis. Yasutomi et al found that increasing cold ischemia time was significantly associated with an increased risk for arterial complications, confirming a previous report by the Mount Sinai group.3 This observation underscores the importance, and sometimes difficulty, of finding a suitable recipient for small pediatric donors quickly. Apart from the clear agreement between the 2 studies that hepatic artery thrombosis is increased in adult recipients receiving small pediatric donor livers, both studies also make similar observations regarding the importance of small-for-size donors. This concern was first studied in establishing the size limitations for living related grafts. The central question is whether a relatively small hepatocyte mass compared with the larger recipient size is detrimental physiologically. Early coagulopathy, prolonged cholestasis, and a hyperperfusion injury from excessive portal vein inflow have been described.4 The Mayo Clinic study found that both graft loss and vascular complications were related to discrepancies in the size of the donor as compared with the recipient. Using body surface area (BSA) as a correlate of donor liver volume, they report a significant increase in both graft loss and vascular complications, as the donor-to-recipient BSA ratio becomes more discordant. The Mount Sinai study addresses the issue more precisely by determining the ratio of donor liver weight to estimated recipient liver weight (DLW/ERLW). Recipients of DLW/ERLW #0.4, a cutoff previously reported to carry a high risk of graft loss and complications,5 had a significantly decreased 1-year graft survival compared to recipients of livers with a DLW/ERLW $0.4. These authors also make the important observaFrom the Department of Pediatrics and Surgery, UCLA Medical Center, Los Angeles, CA. Address reprint requests to Sue McDiarmid, MD, UCLA Medical Center, Room 12-383 MDCC, 10833 LeConte Ave, Los Angeles, CA 90095-1752. Telephone: 310-206-6134; FAX: 310-206-0203; E-mail: SMcDiarmid@mednet.ucla. edu Copyright © 2001 by the American Association for the Study of Liver Diseases 1527-6465/01/0701-0015$3.00/0 doi:10.1053/jlts.2001. 21699