The minimal important difference for target lobe volume reduction following endoscopic valve therapy in patients with advanced emphysema

Abstract

Objective: Endoscopic valve therapy aims at target lobe volume reduction (TLVR) that is associated with improved lung function, exercise tolerance and quality of life in emphysema patients. In several trials, a TLVR greater than 350 ml was considered to be indicative of positive response to treatment. However, it is not really known what size of TLVR can be considered as being crucial following valve implantation. Methods: TLVR, FEV1 (forced expiratory volume in 1 second), RV (residual volume) and 6-MWT (6-minute-walk test) were assessed prior and around 3 months after valve implantation in 119 patients treated from 2012-2013. TLVR was calculated based on MDCT scan analysis using quantitative imaging software (Apollo; VIDA Diagnostics, Coralville, IA). MID estimates were calculated by anchor-based methods (anchors: FEV1, 6-MWT, RV) and by distribution-based methods. Results: Patients treated by valves experienced a mean change of 0,11l in FEV1, of -0,51l in RV, of 46,6m in 6-MWT and a mean TLVR of 955ml. Using a linear regression based on each of the three anchors, and ROC analysis based on ΔFEV1 and ΔRV, the estimated MID for TLVR was between 890 ml and 1070 ml (between 41% and 54% of the baseline target lobe volume). Conclusion: These MID estimates for TLVR derived from the anchor-based method that identifies precisely the patients clinical outcome are much higher than assumed in previous trials and are useful for sample size determination in new studies.