Clinically meaningful changes in quantitative measures of asthma severity

Objective: To determine minimum clinically meaningful improvements in peak expiratory flow rate (PEFR) and dyspnea visual analog score (VAS) in patien ts with acute asthma exacerbation. Methods: Patients presenting to the emer gency department (ED) with acute asthma exacerbation were eligible. The PEF R and VAS were assessed at presentation and after initial asthma therapy. D uring reassessment, subjects were asked to describe their asthma symptoms a s "much better," "a little better." "no change," "a little worse," or "much worse." Correspondence between self-reported improvement and changes in PE FR and VAS was assessed. The "minimum clinically significant change" in eit her index was defined as the difference between pre- and posttreatment meas ures in subjects reporting their symptoms "a little better." Results: One h undred fifty-six subjects were included. Asthma symptoms were "much better" in 99 (64%), "a little better" in 41 (26%), and "unimproved" (composed of patients describing symptoms as "no change," "a little worse," or "much wor se") in 16 (10%). The mean VAS change among the "a little better" subjects was 2.2 cm (95% CI = 1.1 to 3.4), significantly greater than the -0.4 cm (9 5% CI = -2.1 to 1.4) change in the "unimproved" subjects. The mean change i n percent predicted PEFR among the "a little better" subjects was 11.9 (95% CI = 7.3 to 16.1), not statistically different from the change of 6.1 (95% CI = 1.1 to 11.3) in the "no change" subjects. The "much better" group sho wed significantly greater changes in both measures than either of the other groups. A VAS change of greater than or equal to 0.5 cm reliably discrimin ated between subjects with and without symptom improvement. Conclusions: Im provements in VAS of 2.2 cm and in predicted PEFR of about 12 percentage po ints are minimal clinically significant improvements during ED asthma thera py. The dyspnea VAS is valid in assessing symptomatic changes and may detec t small subjective improvements better than the PEFR.