Minimal Important and Detectable Differences of Respiratory Measures in Outpatients with AECOPD^†

Interpreting clinical changes during acute exacerbations of chronic obstructive pulmonary disease (AECOPD) is challenging due to the absence of established minimal detectable (MDD) and important (MID) differences for most respiratory measures. This study established MDD and MID for respiratory measures in outpatients with AECOPD following pharmacological treatment. COPD assessment test (CAT), modified Borg scale (MBS), modified British Medical Research Council (mMRC) questionnaire, peripheral oxygen saturation (SpO₂), computerised respiratory sounds and forced expiratory volume in one second (FEV₁) were collected within 24-48 hour of an AECOPD and after 45 days of pharmacological treatment. MID and MDD were calculated using anchor- (receiver operating characteristic and linear regression analysis) and distribution-based methods (effect size, SEM, 0.5*SD and MDC95) and pooled using Meta XL. Forty-four outpatients with AECOPD (31♂; 68.2 ± 9.1 years; FEV₁ 51.1 ± 20.3%predicted) participated. Significant correlations with CAT were found for the MBS (r = 0.34), mMRC (r = 0.39) and FEV₁ (r = 0.33), resulting in MIDs of 0.8, 0.5-0.6 and 0.03L, respectively. MDD of 0.5-1.4 (MBS), 0.4-1.2 (mMRC), 0.10-0.28L (FEV₁), 3.6-10.1% (FEV₁%predicted), 0.9-2.4% (SpO₂), 0.7-1.9 (number of inspiratory crackles), 1.1-4.5 (number of expiratory crackles), 7.1-25.8% (inspiratory wheeze rate) and 11.8-63.0% (expiratory wheeze rate) were found. Pooled data of MID/MDD showed that improvements of 0.9 for the MBS, 0.6 for the mMRC, 0.15L for the FEV₁, 7.6% for the FEV₁%predicted, 1.5% for the SpO₂, 1.1 for the inspiratory and 2.4 for the number of expiratory number of crackles, 14.1% for the inspiratory and 32.5% for the expiratory wheeze rate are meaningful following an AECOPD managed with pharmacological treatment on an outpatient basis.