Respiratory resistance in the emergency department - A reproducible and responsive measure of asthma severity

Objectives: To determine, in preschool children with an acute asthma exacerbation, the responsiveness to change of respiratory resistance measurements obtained by the forced oscillation (Rfo) technique, and to identify the magnitude of change indicative of airway obstruction reversibility. Design/setting: A prospective observational study of 114 children, aged 3 to 17 years, untrained in the Rfo technique and treated for acute asthma in a tertiary-care pediatric emergency department (ED). Measurements: A physical examination followed by three measurements of respiratory resistance by forced oscillation were obtained at 8 Hz (Rfo(8)) and at 16 Hz (Rfo(16)). In cooperative children, routine spirometry that included FEV1 was also performed on the Gusto Vit R (Custo Med; Munich, Germany). All measurements were obtained twice during the course of the ED treatment, before and after treatment with nebulized bronchodilators. Results: The Rfo(8) and Rfo(16) measurements were highly reproducible (reproducibility coefficients >0.85). Both the Rfo(8) and Rfo(16) were at least as responsive to change (responsiveness coefficients of 2.3 and 1.2, respectively) as was FEV1 (2.0) and the four clinical signs most sensitive to change (0.6 to 1.0). A 19% change in Rfo(8) was suggestive of significant reversibility. Conclusions: In the assessment of children aged greater than or equal to 3 years with acute asthma exacerbation, the respiratory resistance measurements are highly reproducible and responsive to change, particularly when obtained at 8 Hz. A 19% change from baseline Rfo(8) is suggestive of reversibility. This technique appears to be an attractive alternative in the evaluation of children who are too young or too sick to perform spirometry reproducibly.