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

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Abstract Rationale: Oscillometry is a feasible and safe method to measure lung function in children with asthma exacerbations in the emergency department (ED), but its utility to measure respiratory impedance as an objective marker of ED therapeutic response is unknown. We aimed to determine the associations between respiratory impedance metrics and asthma exacerbation severity and treatment response in the pediatric ED. Methods: Prospective study of children 4-18 years presenting to a tertiary-care pediatric ED for asthma exacerbations. Respiratory impedance measured with tremoFlo c-100 (Thorasys), vital signs, and Pediatric Asthma Score (PAS) were collected before (T1) and 15 minutes after (T2) initial ED treatment with inhaled bronchodilators and systemic corticosteroids. Respiratory impedance measures included: 1) low-frequency resistance (R7), measure of total airway resistance; 2) reactance area (AX), measure of airway stiffness, and 3) frequency dependence of resistance (R7-19), measure of peripheral airways resistance. Z-scores for R7 and AX were computed from reference equations based on height. Multivariable regression analyses, guided by LASSO feature selection, estimated the associations between respiratory impedance and exacerbation severity (mild: PAS 5-7; moderate/severe PAS 8-15) and treatment response (defined as not requiring additional asthma therapies [i.e., continuous nebulized albuterol, intravenous (IV) magnesium, IV terbutaline, IM epinephrine] or hospitalization). Receiver operating characteristic (ROC) curves and area under the curve (AUC) C-statistic were used to assess the predictive accuracy of respiratory impedance measures and vital signs (at T1 and T2-T1 difference) in differentiating exacerbation severity, need for additional therapies, hospitalization and treatment response. Results: Total of 177 participants were enrolled; 143 (81%) provided a valid initial oscillometry assessment. Forty-seven percent had a moderate/severe exacerbation, 33% required additional asthma therapies, 22% required hospitalization and 61% met the treatment response definition. Greater initial R7-19T1 (OR 1.4; 95% CI, 1.06-1.92) and AXT1 (OR 1.28; 95% CI, 1.05-1.58) were associated with higher odds of moderate/severe exacerbation. Greater initial R7-19T1 was associated with decreased odds of treatment response (OR 0.74; 95% CI, 0.54-0.99). ROC analyses showed a combination of respiratory impedance measures and vital signs best differentiated exacerbation severity (AUC 0.73; 95% CI:0.63-0.82), treatment response (AUC 0.69; 95% CI:0.58-0.80), and hospitalization (AUC 0.78; 95% CI:0.67-0.88) (Figure). Conclusion: Oscillometry is a useful objective pulmonary measure of disease severity and treatment response for asthma exacerbations in the ED. A combination of respiratory impedance measures and vital signs have potential to guide ED clinical decisions and improve outcomes for children with asthma exacerbations.

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