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Nitrogen multiple-breath washout (N 2 MBW) is increasingly used in patients with cystic fibrosis. The current European Respiratory Society/American Thoracic Society consensus statement for MBW recommends the rejection of measurements with leaks. However, it is unclear whether this is necessary for all types of leaks. Here, our aim was to 1) model and 2) apply air leaks, and 3) to assess their influence on the primary MBW outcomes of lung clearance index and functional residual capacity. We investigated the influence of air leaks at various locations (pre-, intra- and post-capillary), sizes, durations and stages of the washout. Modelled leaks were applied to existing N 2 MBW data from 10 children by modifying breath tables. In addition, leaks were applied to the equipment during N 2 MBW measurements performed by one healthy adolescent. All modelled and applied leaks resulted in statistically significant but heterogeneous effects on lung clearance index and functional residual capacity. In all types of continuous inspiratory leaks exceeding a certain size, the end of the washout was not reached. For practical application, we illustrated six different "red flags", i.e. signs that enable easy identification of leaks during measurements. Air leaks during measurement significantly influence N 2 MBW outcomes. The influence of leaks on MBW outcomes is dependent on the location, relation to breath cycle, duration, stage of washout and size of the leak. We identified a range of signs to help distinguish leaks from physiological noise., Competing Interests: Conflict of interest: None declared.

Background: Ivacaftor acts as a potentiator of the cystic fibrosis transmembrane conductance regulator (CFTR) and increases the transepithelial chloride transport of CFTR in 9 of 10 known gating mutations causing cystic fibrosis. S549R is a rare gating mutation considered to be less sensitive to potentiators than all other gating mutations., Case Presentation: We report our first experience with ivacaftor in an 8-year-old boy with the rare S549R gating mutation. Besides subjective clinical improvements, the sweat chloride level and the lung clearance index decreased impressively within a few weeks of treatment while forced expiratory volume in the first second values remained in normal range., Conclusion: We emphasize the value of measuring small airway function by lung clearance index as an outcome measure for new interventions targeting the correction of the CFTR defect at an age before traditional lung function parameters start to deteriorate.

Unlabelled: Recently, Aerococcus urinae, primarily recognized as a common pathogen in elderly women, has been reported to cause an extremely unpleasant odour of the urine in paediatric patients similar to trimethylaminuria (fish odour syndrome). Herein, we present a case of A. urinae urinary tract colonization in a 12-year-old otherwise healthy boy, who finally refused micturition outside from his home environment as a result of the unpleasant odour. Within the last year, three cases (including our own) of A. urinae colonization causing foul-smelling urine in healthy children have been published, suggesting that this condition might be as frequent as trimethylaminuria. In case of polymicrobial growth in a urine specimen, A. urinae as the leading pathogen will usually be missed by routine bacteriological investigation. Novel bacteriological techniques such as MALDI-TOF MS provide a rapid tool to recognize this pathogen in urine., Conclusion: As treatment of A. urinae infection is simple, we recommend that in healthy children with malodorous urine, this pathogen is excluded before the initiation of costly metabolic investigations.