Prevalence and risk factors of fixed airway obstruction in children with asthma

Background: A subgroup of children with asthma may develop accelerated decline in lung function and fixed airway obstruction (FAO). Aim was to determine the prevalence and risk factors of FAO in children with asthma. Methods: In this cross sectional cohort study, we recruited children aged 6-18 years with asthma, followed up at KK Women’s and Children’s hospital, Singapore. They had comprehensive clinic review and spirometry at 3-4 months interval, and the data was captured in an electronic database. FAO was defined as post bronchodilator (salbutamol 400µg) FEV1 % predicted Results: 221 children (mean[SD] age=12.6[3.3] years, 58% males, mean[SD] duration of follow up=8.4[3.4] years) were studied. 46(20.8%) children had FAO. 19(8.6%) children had post bronchodilator FEV1 % predicted ≤70%. There was no significant difference in age, race, gender, age at onset of asthma, duration of asthma, Fractional Exhaled Nitric Oxide (FeNO), Asthma Control Test (ACT) score, eczema, allergic rhinitis, allergen sensitisation, Inhaled Corticosteroid (ICS) dose, treatment with long acting beta agonist (LABA), Leukotriene receptor antagonist (LTRA) and passive smoke exposure between those with or without FAO. On multivariate regression analysis, poor adherence with asthma controller therapy (p=0.10) and longer duration of ICS treatment (p=0.006) were the two factors found to be most significantly associated with the FAO phenotype. Conclusions: In our cohort, approximately one fifth of children with asthma have FAO phenotype. Longer duration of ICS therapy and poor treatment adherence are risk factors for developing FAO.