Oscillometry Measures the Response to Acute Asthma Therapy in the Pediatric Emergency Department

Rationale: Oscillometry is a feasible and safe method to measure pulmonary function in children with asthma exacerbations in the emergency department (ED), but its utility to measure respiratory impedance as an objective marker of response to initial acute asthma treatments is unknown. Objectives: We sought to determine the associations between respiratory impedance-derived metrics and asthma exacerbation severity and treatment response in the pediatric ED. Methods: We conducted a prospective study of children, ages 4-18 years, who presented to a tertiary-care pediatric ED for asthma exacerbations. Respiratory system impedance was measured with oscillometry before and after initial treatment with inhaled bronchodilators and systemic corticosteroids. Regression models estimated the associations between respiratory impedance-derived metrics (low-frequency resistance, R7, a measure of total airway obstruction; frequency dependence of resistance, R7-19, a measure of peripheral airway resistance; and reactance area, AX, a measure of lung tissue stiffness and variability in ventilation), vital signs, and clinical outcomes. Receiver operating characteristic analyses were used to quantify the ability of respiratory impedance-derived metrics and vital signs to discriminate outcomes. Results: Of 177 participants, 144 (81%) completed a valid initial oscillometry assessment. Forty-seven percent had moderate or severe exacerbations, and 61% met the treatment response definition. Frequency dependence of resistance (R7-19: adjusted odds ratio [aOR], 1.39; 95% confidence interval [CI] = 1.08-1.83) and area of reactance (AX: aOR, 1.28; 95% CI = 1.05-1.58), were associated with higher odds of moderate or severe exacerbation. Greater initial R7-19 was associated with decreased odds of treatment response (aOR, 0.75; 95% CI = 0.57-0.98). A combination of impedance-derived metrics and vital signs best differentiated exacerbation severity (area under the curve [AUC] = 0.73), treatment response (AUC = 0.69), and hospitalization (AUC = 0.78). Conclusions: Respiratory impedance-derived metrics (R7, R7-19, and AX), in combination with vital signs, can guide ED clinical decisions and improve outcomes for children with asthma exacerbations.