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Lung Clearance Index to Track Acute Respiratory Events in School-age Children with Cystic Fibrosis.

OBJECTIVE
The lung clearance index (LCI) is responsive to acute respiratory events in preschool children with cystic fibrosis (CF) but its' utility to identify and manage these events in school-age children with CF is not well defined.


METHODS
In a multisite prospective observational study, LCI and forced expiratory volume in 1 second (FEV1) were measured quarterly and during acute respiratory events. Linear regression was used to compare relative changes in LCI and FEV1 % predicted at acute respiratory events. Logistic regression was used to compare the odds of a significant worsening in LCI and FEV1 % predicted at acute respiratory events. Generalized estimating equation models were used to account for repeated events in the same subject.


RESULTS
A total of 98 children with CF were followed for two years. There were 265 acute respiratory events. Relative to a stable baseline measure, LCI (+8.9%; 95% CI 6.5 to 11.3) and FEV1% predicted (-6.6%; 95% CI -8.3 to -5.0) worsened with acute respiratory events. A greater proportion of events had a worsening in LCI compared to a decline in FEV1% predicted (41.7% vs 30.0%; p=0.012); 53.9% events were associated with worsening in LCI or FEV1. Neither LCI nor FEV1 recovered to baseline values at the next follow-up visit.


CONCLUSIONS
In school-age children with CF, LCI is a sensitive measure to assess lung function worsening with acute respiratory events and incomplete recovery at follow-up. LCI and FEV1 in combination capture a higher proportion of events with functional impairment.