Bigger is Better - Oversizing May Improve Survival in Single Lung Transplantation for Pulmonary Fibrosis

Abstract

Purpose The donor to recipient predicted total lung capacity (pTLC) ratio is routinely used to guide size matching. Guidelines do not differentiate between underlying diseases. We aimed to assess if post-transplant outcomes for pulmonary fibrosis (PF) single lung transplant recipients is improved when receiving an oversized lung. Methods Data on all adult patients who received a first single or bilateral lung-only transplant in the UK between 2007 and 2016 were obtained from the UK Transplant Registry. Donor to recipient pTLC mismatch ratio was used to assign patients to three groups: 0%. Post-transplant survival was assessed using Kaplan-Meier survival curves and log-rank tests. The pTLC mismatch ratio was further analysed as a continuous non-linear variable using an unadjusted Cox Proportional Hazards Regression model. A natural cubic spline was used to represent non-linearity, enabling cubic expressions between “knots” at the 5%, 35%, 65% and 95% percentiles. Results 321 patients were included in our cohort; 243 (75.7%) were male, mean age of 56 years. Mean donor pTLC was 5.7L, mean recipient pTLC was 6.4L, mean pTLC mismatch ratio was -10.1%. Kaplan-Meier analysis suggested no significant difference between the mismatch categories upon 90 day (p=0.28) or 1 year (p=0.16) post-transplant survival, with borderline significance 5 years post-transplant (p=0.08). No significant differences were found analysing the bilateral lung transplant cohort alone. Analysis of single lung recipients showed borderline significance at 1 year (p=0.07) and significant difference 5 years post-transplant (p=0.05). An unadjusted Cox Regression model was therefore applied to single lung transplant recipients only, demonstrating a significant non-linear effect of the pTLC mismatch ratio at 90 days and borderline effect at 1 year and 5 years post transplant (p=0.05, p=0.09 and p=0.06, respectively). The non-linear effect detected for 90 day post-transplant survival was such that the hazard of death decreases the larger the mismatch, until approximately +/-20%. A similar effect was detected for 1 year and 5 years post-transplant, but to a lesser extent. Conclusion Oversizing donor lung allografts in patients receiving a single lung transplant for pulmonary fibrosis may improve survival in both the short and long term.