Noninvasive bedside assessment of acute asthma severity using single-breath counting

The single-breath counting (SBC) method for assessment of asthma exacerbation severity has been evaluated in adults during exacerbations and in pediatric patients during routine settings. Single-breath counting has not been evaluated in children during exacerbations. We sought to assess criterion validity and responsiveness of SBC with percent-predicted FEV1 (%FEV1) and the Pediatric Respiratory Assessment Measure (PRAM), a validated acute asthma severity score.

We prospectively enrolled subjects aged 7 to 17 years with acute asthma exacerbations. Single-breath counting, %FEV1, and PRAM were obtained before treatment and 2 hours after initiating therapy. Multivariable linear regression models were used to examine associations of pretreatment SBC with %FEV1 and PRAM (criterion validity) and 2-hour change of these measures (responsiveness). With a 2-sided α of 0.05, SBC SD of 8.5, and 90% power to detect an adjusted R of greater than 0.36 for SBC with each outcome measure, a minimum sample of 20 participants was necessary.

From June to November 2011, 51 participants were enrolled, with median (interquartile range) age of 8.46 years (6.92-11.4 years); male sex, n = 40 (78%); and African American race, n = 33 (64%). Before treatment, 42 (92%) were able to successfully perform SBC, and 24 (51%) %FEV1. Median pretreatment SBC obtained was 16 (10-24); %FEV1, 50 (26-71); and PRAM, 5 (1-5).

Single-breath counting demonstrates modest criterion validity for predicting the pretreatment PRAM score and a trend for predicting %FEV1. Single-breath counting does not appear to be responsive to change of these measures in response to treatment and has limited validity as a measure of acute asthma severity.