Study objective: Bronchodilator response criteria have been determined in adults; however, data applicable to children and adolescents are scarce. We measured pulmonary function in asthmatic patients to determine the bronchodilator response.
Design: A blind study.
Setting: Outpatient clinic of Pneumology Unit, Instituto da Criança and Center of Asthma Care and Research, University Hospital, University of São Paulo Medical School.
Patients: Sixty patients aged 6 to 20 years (median, 12 years).
Interventions: Spirometry and plethysmography were performed before and after blind placebo and bronchodilator inhalation (400 μg salbutamol by metered-dose inhaler).
Measurements and results: Approximately 90% of the patients had mild-to-moderate persistent asthma. The mean FEV1 at baseline was 79.6% of the predicted value. Distribution of variations of the different pulmonary function parameters was analyzed after placebo inhalation. The 95th percentile was adopted as a criterion for a significant bronchodilator response. After the bronchodilator test, the patients were classified based on criteria derived from the placebo inhalation and the American Thoracic Society guidelines. Parameters established as cutoff values were 265 mL, 14.2% and 10% FEV1 expressed as absolute volume, percentage compared with that at baseline and percentage of the predicted value, respectively, and 55% specific airway conductance (sGaw) expressed as a percentage compared with that at baseline. Based on the spirometric data, 37 patients (61%) had reversibility of obstruction, while 48 patients (80%) were classified as responders based on the analysis of variations in sGaw. The classifications based on variations in FEV1 expressed as absolute volume and percentage of the predicted value showed a substantial correlation with the international classification.
Conclusions: The cutoff values established for the assessment of the bronchodilator response in the present population agree with those reported in the literature. sGaw was the most sensitive parameter for the identification of changes in airway caliber.