Utility of Six-Minute Walk Distance in Predicting Outcomes after Lung Transplant: A Nationwide Survival Analysis

Abstract

<h3>Purpose</h3> Currently the Lung Allocation Score (LAS) dichotomizes 6-minute walk distance (6MWD) at 150 ft. We hypothesized that increasing 6MWD considered as a continuous variable would be associated with improved survival after lung transplant. <h3>Methods and Materials</h3> Adult, first time, lung-only transplantations per the United Network for Organ Sharing database from 04/2005-12/2011 were analyzed. Generalized linear models were used to determine the association between preoperative 6MWD and post-transplant survival after adjusting for potential confounders. <h3>Results</h3> 9,013 patients were included for analysis. The median 6MWD was 810 feet (25th-75th percentiles=520-1100 feet). Increasing 6MWD quartile was associated with significantly improved survival. [figure 1] As a continuous variable, increasing 6MWD was associated with significantly lower mortality at 90-days [adjusted odds ratio (AOR) per 500 feet 0.90, 95% confidence interval (CI) 0.83-0.98, p=0.02], 1-year (AOR 0.89, CI 0.83-0.95, p<0.001), and 3-years (AOR 0.92, CI 0.85-1.00, p=0.04) as well as reduced overall hazard of death (adjusted hazard ratio per 500 feet 0.86, CI 0.82-0.90, p<0.0001). Based on recursive partitioning, stratification of 6MWD by over/under 730 feet provided maximal separation in 1-year mortality. <h3>Conclusions</h3> 6MWD as a continuous variable is significantly associated with post-transplant survival. Strategies to improve patient functional status preoperatively, including aggressive rehabilitation efforts, could therefore impact post-transplant survival. Future iterations of the LAS should consider the full range of 6MWD values in order to provide maximum prognostic information regarding post-transplant survival.