Minimal important difference of lobar volume reduction after valve treatment for emphysema

Abstract

Background: Target lobar volume reduction (TLVR) is an important efficacy outcome measure for bronchoscopic lung volume reduction treatment using one-way endobronchial valves (EBV) in patients with severe emphysema. The commonly used cut-off value for TLVR that expresses a percievable clinical benefit is -350ml. However, a scientifically determined minimal important difference (MID) for TLVR never has been published. Aim: The objective of this study was to determine the MID for TLVR in patients who were treated with EBV. Methods: A total of 318 severe emphysema patients from 2 EBV trials were analysed. TLVR was measured using quantitative CT analysis by measuring the difference in target lobar volume between baseline and 6 months follow-up. Anchor-based methods were used to define the TLVR MID at 6 months follow-up. Forced expiratory volume in 1 second (FEV1), residual volume (RV) and St. George’s Respiratory Questionnaire (SGRQ) were used as anchors. Results: The calculated TLVR MID with each anchor was: FEV1 −587ml (relative MID −25.2%), RV −534ml (relative MID −21.3%) and SGRQ -560ml (relative MID -20.6%). The combined MID (average of the 3 anchor-based MIDs) was −563ml (relative MID −22.4%). Conclusions: Using the anchor-based method for three validated efficacy endpoints we established a TLVR MID of -563ml (-22.4%) in patients with severe emphysema at 6 months follow-up after EBV treatment. This value can be useful for both interpreting the results from trials and clinical practice, as well as for designing future studies on lung volume reduction.