Objectives: To assess, in acutely ill asthmatic children, the feasibility of obtaining reproducible measurements of two independent lung function tests, namely spirometry and respiratory resistance, using the forced oscillation technique (Rfo).
Design/setting: A prospective observational study of 150 previously untrained children, aged 2 to 17 years, treated for acute asthma in a tertiary-care pediatric emergency department.
Measurements: Following a standardized physical examination, three measurements of respiratory resistance by forced oscillation were attempted at 8 Hz (Rfo8) and at 16 Hz (Rfo16), followed by spirometry, all using the same instrument (Custo Vit R; Custo Med; Munich, Germany).
Results: On the initial assessment, 98 (65%) children, aged 2 to 17 years, were able to reproducibly perform the Rfo8 measurement, 77 (51%) were able to reproducibly perform the Rfo16 measurement, while only 65 (43%) subjects managed to reliably perform spirometry. A notable proportion of preschool-aged children cooperated with the Rfo8 technique: 19% of 3-year-olds, 40% of 4-year-olds, and 83% of 5-year-olds. The superior success rate with Rfo8 as compared with spirometry was seen in all age groups but was most striking both in preschoolers (relative risk [RR]=10.5; 95% confidence interval [CI], 8.0 to 13.8) and in children aged 6 to 9 years (RR= 1.28; 95% CI, 1.18 to 1.39). Rfo8 values correlated significantly with clinical markers of asthma severity such as respiratory rate (r=0.38) and heart rate (r=0.23) as well as with FEV1 values (r2=0.73).
Conclusions: This study demonstrates the feasibility of obtaining reproducible measurements of respiratory resistance in a notable proportion of untrained, acutely ill, asthmatic children. The forced oscillation technique appears as an attractive alternative to objectively assess lung function in children too young or too ill to cooperate with spirometry.