WTC 2014 Report: The effect of transplant centre volume on mortality of liver transplant recipients

By Aliaksei Pustavoitau et al, Johns Hopkins University School of Medicine, USA.  Although the overall mortality in the first year after liver transplantation is decreasing each year, centres with a low annual volume of transplants tend to have higher mortality rates. A data review by a team of researchers at Johns Hopkins shows that patients having liver transplantations in centres where between 16 and 20 liver transplantations are performed per year are at the highest risk of dying in the first year post-transplant. The results of the study were presented by Professor Aliaksei Pustavoitau.

That centre volume may affect mortality had been shown in previous studies. A study published in 1999, and thus representing the era prior to the use of MELD score to quantify end-stage liver disease for the purpose of selecting patients for transplantation, showed that centres in the United States that performed fewer than 20 liver transplantations annually had higher mortality rates (28.3% versus 20.1% in centres with annual volumes of 20 or more procedures; p<0.001) [1]. MELD scoring was introduced in 2002, and an analysis published in 2006 suggested that annual volume was no longer influencing mortality in the MELD era: patients operated on in low-volume centres had an unadjusted mortality rate of 10.9% versus 9.5% in high-volume centres, but this hazard did not reach statistical significance after adjusting for disease severity and other donor and recipient factors (HR 0.99; 95% CI 0.99,1.00) [2]. The objective of Professor Pustavoitau’s analysis was to determine how first-year mortality after liver transplantation has developed in the last decade, overall and in relation to patient age and functional capacity.

The analysis comprised data from the Scientific Registry of Transplant Recipients (SRTR) which contains data from all transplant centres in the United States, entered between 1 January 2003 and 31 December 2011. Data from transplantations in adult patients using whole livers from deceased donors were included in the analysis. Centres were classified as low, intermediate-low, intermediate-high or high volume based on the annual number of liver transplants. The number of centres and volume definitions were adjusted at each year of the analysis. Functional capacity was defined based on the extent to which the patient required full assistance with daily activities. Univariate and multivariate Cox regression was used for determining the link between centre volume and all-cause mortality, with multiple imputation to account for handle missing data.

A total of 49,170 patients at 122 centres were included in the analysis. The lower-volume centres were characterised by doing fewer liver transplantations after circulatory death, using fewer hepatitis C-positive livers, and having fewer patients with previous abdominal surgery or portal vein thrombosis. Overall, mortality in the first year post-transplant decreased from around 15% in 2004 to around 7% in 2012; this trend was evident in all volume quartiles. Multivariate analysis showed a significantly higher hazard of mortality in low-volume centres (adjusted hazard ratio [HR] 1.12; 95% confidence interval [CI] 1.01, 1.24) compared with high-volume centres.

A secondary objective was to determine whether the cut-off point of 20 transplantations per year is still relevant for defining low-volume centres. Volume categories were analysed with respect to hazard ratios, and a centre volume of 16-20 transplantations per year was found to be associated with the greatest risk of death (adjusted HR 1.21; 95% CI 1.06, 1.39). Professor Pustavoitau concluded that although mortality is declining overall, low annual transplant volumes remain significantly associated with increased mortality even in the most recent era.

References

1.         Edwards, E.B., et al., The effect of the volume of procedures at transplantation centers on mortality after liver transplantation. N Engl J Med, 1999. 341(27): p. 2049-53.

2.         Northup, P.G., et al., Survival after adult liver transplantation does not correlate with transplant center case volume in the MELD era. Am J Transplant, 2006.6(10): p. 2455-62.