The Lung Clearance Index (LCI) is an index derived from washout recordings, able to detect early peripheral airway damage in subjects with cystic fibrosis (CF) with a greater sensitivity than spirometry. LCI is a marker of overall lung ventilation inhomogeneity; in fact, as pulmonary ventilation worsens, the number of tidal breaths and the expiratory volumes required to clear the lungs of a marker gas are increased, as documented by a greater value. In the field of CF, LCI allows indirect investigation of the small airways (< 2 mm) the site where, from a pathophysiologic point of view, the disease begins due to the defect of the CF transmembrane-conductance regulator (CFTR) protein. Infant pulmonary function changes seem to occur before clinically overt symptoms of lower respiratory illness occur. When performing the test, it is important to refer to the American Thoracic Society and European Respiratory Society consensus statements and apply a strict standardization. In Italy the first tests were carried out in 2014 for research purpose and now approximately 10 centers are collecting data and are experiencing a consistency in repeating exams. Currently in Italian centers children at pre-school age are the main target: in this population it is important to have a sensitive and feasible test, non-invasive, that can be performed at tidal volume without sedation, and requiring minimal cooperation and coordination, and that can be used longitudinally over time. Another target could be the transplanted subjects to detect early signs of lung function decline. The content of this paper captures the experience and discussions among some of the Italian centers where LCI is currently used for research and/or in clinical practice about the method and the need to have a common approach. The aim of this paper is not to describe the methodology of MBW, but to inform the pediatric community about the possible application of LCI in CF.

Elexacaftor/tezacaftor/ivacaftor (ETI) is a cystic fibrosis (CF) transmembrane conductance regulator modulator, which has shown efficacy in people with CF (pwCF) carrying the F508del (F) variant, both in homozygosity and heterozygosity with a minimal function (MF) variant. Limited data exist on the effects of ETI in pwCF with advanced lung disease. Our aim was to investigate ETI safety and effectiveness in this patient group in a real-life setting over 2 years. A multicenter observational cohort study was designed to gather real-world information on the effect of ETI treatment on CF patients (aged >12 years, genotype: F/MF mutation) with advanced lung disease as defined by a FEV1 < 40% predicted. Retrospective demographic and clinical data were recorded for the two years preceding and the two years following ETI initiation. The following outcomes were investigated: treatment-associated adverse events (AEs), drug interruptions (temporary or permanent), variations in percent predicted FEV1 (ppFEV1), sweat chloride concentration (SwCl), antibiotic use, body mass index (BMI), and quality of life. A total of 124 (51.6% males) pwCF were treated with ETI over 2 years. The median (IQR) age and ppFEV₁ were 34 (26, 43) years and 34 (29, 41) percentage points, respectively. ETI was discontinued in two pwCF due to lung transplantation, and temporarily interrupted in two because of skin rash, and in three following elevated levels of aminotransferase. Most AEs were mild and short-lasting. In 12.1% pwCF, we registered an increase greater than twice the upper limit of the normal range in alanine aminotransferase, and in 16% we registered an increase in conjugated bilirubin with no increase in aminotransferase. Both increases were recurrent in about half of the subjects. The mean differences (95% CI) for ppFEV₁ and SwCl, assessed as mean values in the pre-ETI and ETI treatment periods, were +11.8 (11.1 to 12.6) and −43.7 (−47.6 to −39.9) mmol/L. A modest increase in ppFEV₁ persisted during the second year of treatment. Number of oral and IV antibiotic cycles/year, as well as hospitalizations/year, decreased significantly from 3.6 to 1.2, from 2.4 to 0.6, and from 2.1 to 0.5 during ETI treatment. A total of 8 of 16 (50%) pwCF were taken off the waiting list for lung transplantation, and significant reductions in the percentages of pwCF using long-term oxygen therapy and non-invasive ventilation were observed. A poor concordance between ppFEV1 and SwCl was found. In only 3/82 (3.7%), subjects with chronic airway infection by Pseudomonas aeruginosa cultures were always negative during ETI treatment. In CF patients with advanced lung disease on ETI treatment, we observed an improvement in a number of clinically significant outcomes over a 2-year study period. However, several additional observations, such as liver dysfunction, variable degrees of lung function improvement, and limited impact on chronic airway infection, underscore the fact that the benefit–risk profile of ETI treatment in cystic fibrosis patients with advanced lung disease has not been fully elucidated and warrants prolonged-term monitoring.