Lung Clearence Index is Sensitive to Small Airway Disease in Pediatric Lung Transplant Recipients

Background The principal obstacle to long term survival after lung transplant is chronic lung allograft dysfunction, which primarily affects the small airways. Post-transplant patients are monitored with spirometry, which is a generally insensitive detector of small airways obstruction. The lung clearance index is a measure obtained during multiple breath washout maneuvers. We hypothesized that among lung allograft recipients, lung clearance index will detect small airway disease not evident with spirometry. Methods Fifteen patients were enrolled in this study, five already had a diagnosis of chronic lung allograft dysfunction. To the established post-transplant routine care protocol, we added multiple breath washout as an additional index of peripheral airway function. Results 87.9% of trials yielded valid measurements and single maneuvers ranged from two to 8 minutes. Lung clearance index did not call any false negatives; no patients were considered obstructed by FEV1 , but normal by lung clearance index. At enrollment, there were six patients without chronic lung allograft dysfunction that measured an elevated lung clearance index, four of which progressed to chronic lung allograft dysfunction. Of those four, only two would have been identified by a decrease in FEV1. Conclusions Lung clearance index identified lung allograft dysfunction in more patients than the use of standardized spirometric measures, including patients identified with abnormal FEV1 . This data suggests that lung clearance index from multiple breath washout may be a more sensitive means to detect allograft peripheral airway disease than standard methods for measurement of small airways function.