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

BACKGROUND AND OBJECTIVE: Target lobar volume reduction (TLVR) is an important efficacy outcome measure for bronchoscopic lung volume reduction (BLVR) treatment using one-way endobronchial valves (EBV) in patients with severe emphysema. The commonly used cut-off value for TLVR that expresses a perceivable clinical benefit is -350 mL. However, a scientifically determined minimal important difference (MID) for TLVR never has been published. The objective of the present study was to determine the MID for TLVR on HRCT in patients who were treated with EBV. METHODS: A total of 318 patients with severe emphysema from two BLVR trials were analysed. Anchor-based methods were used to define the TLVR MID at 6 months follow-up. Forced expiratory volume in 1 s (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 -587 mL, RV -534 mL and SGRQ -560 mL. The combined MID (average of the three anchor-based MIDs) was -563 mL. CONCLUSION: Using the anchor-based method, we established a TLVR MID of -563 mL 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.