Lung clearance index is sensitive to small airway disease in pediatric lung transplant recipients.
The principal obstacle to long-term survival after lung transplant is chronic lung allograft dysfunction (CLAD), which primarily affects the small airways. After transplant, patients are monitored with spirometry, which is a generally insensitive detector of small airways obstruction. The lung clearance index (LCI) is a measure obtained during multiple breath washout (MBW) maneuvers. We hypothesized that among lung allograft recipients, LCI would detect small airways disease not detected with spirometry. This study enrolled 15 patients, 5 of whom already had a diagnosis of CLAD. We added MBW as an additional index of peripheral airway function to the established post-transplant routine care protocol. Of trials, 87.9% yielded valid measurements, and single maneuvers were 2-8 minutes. LCI did not yield any false-negative findings-no patients were considered obstructed by forced expiratory volume in 1 second (FEV1) but normal by LCI. At enrollment, 6 patients without CLAD had an elevated LCI, and 4 progressed to CLAD. Only 2 of these 4 patients would have been identified by a decrease in FEV1. LCI identified lung allograft dysfunction in more patients than the use of standardized spirometric measures, including patients with abnormal FEV1. These data suggest that LCI from MBW may be a more sensitive means to detect allograft peripheral airway disease than standard methods for measurement of small airways function.