Nitrogen (N2) multiple breath washout: Assessment of ventilation inhomogeneity in severe paediatric asthma

Introduction: Lung clearance index (LCI) is the main parameter derived from multiple breath washout (MBW), and reflects the degree of ventilation inhomogeneity. Aim: To evaluate LCI derived from N2 MBW in children with difficult-to-control asthma referred to a Severe Asthma Clinic (SAC). Methods: Patients with difficult-to-control asthma were reviewed in the SAC at the John Hunter Children’s Hospital, Newcastle, Australia between 2014 and 2017. All patients were prescribed maximum inhaled corticosteroid therapy plus long-acting beta agonist or/and leukotriene receptor antagonist (LTRA). Spirometry, fraction of exhaled nitric oxide (FeNO), asthma control test (ACT) scores, and N2 MBW (Exhalyer D, Eco Medics AG) were attempted during SAC visits if age-appropriate. Results: 16 subjects were reviewed (age range 2-15 years). At the first SAC visit mean (range) LCI (n=9) was 11.7 (8.4-20.2; 100% abnormal), FEV1 predicted (n=14) was 69% (37-98%), FeNO (n=12) was 28.4 ppb (5.1-87.0 ppb) and ACT score (n=16) was 14 (8-25). 13 out of 14 patients performed subsequent spirometry and mean FEV1 predicted was higher at follow-up (80%; range: 62-103%; p=0.04 for difference to first visit). Follow-up MBW tests are currently being performed in this on-going study. Conclusion: Evidence of ventilation inhomogeneity was present in all patients seen for difficult-to-control asthma in this cohort. Further follow-up is required to clarify if MBW detects the benefits in clinical response observed in spirometry.