Lung function in severe pediatric asthma: a longitudinal study in children and adolescents in Brazil

Background In severe asthma, high doses of inhaled corticosteroids (ICS) are used in order to achieve clinical and functional control. This study aimed to evaluate lung function in outpatients (children and adolescents) with severe asthma in Brazil, all of whom were treated with high doses of ICS. We evaluated all spirometry tests together and by ICS dose: 800 and > 800 µg/day. Methods This was a 3-year longitudinal study in which we analyzed 384 spirometry tests in 65 severe asthma patients (6-18 years of age), divided into two groups by the dose of ICS (budesonide or equivalent): 800 and > 800 µg/day. Results At baseline, the forced expiratory volume in one second (FEV1) and the FEV1/forced vital capacity (FVC) ratio were both < 80% of the predicted values in 50.8% of the patients. The median age of the patients was 10.4 years (interquartile range 7.8-13.6 years). In the sample as a whole, there were significant increases in FEV1% and in the FEV1/FVC% ratio (p = 0.01 and p < 0.001, respectively) over the course of the study. In the > 800 µg/day group, there were no statistical increases or decreases in FEV1, the FEV1/FVC ratio, or forced expiratory flow between 25 and 75% of the FVC (FEF25-75%), when calculated as percentages of the predicted values. However, the z-score for FEF25-75% showed a statistically significant reduction, in the sample as a whole and in the > 800 µg/day group. Also in the > 800 µg/day group, there was a significant reduction in the post-bronchodilator FEV1% (p = 0.004). Conclusions The fact that the spirometric parameters (as percentages of the predicted values) remained constant in the > 800 µg/day group, whereas there was a gain in lung function in the sample as a whole, suggests an early plateau phase in the > 800 µg/day group. However, there was some loss of lung function in the > 800 µg/day group, as evidenced by a decrease in the z-score for FEF25-75%, suggesting irreversible small airway impairment, and by a reduction in the post-bronchodilator FEV1%, suggesting reduced reversibility of airway obstruction. Among children and adolescents with severe asthma, the use of ICS doses higher than those recommended for age does not appear to improve lung function.