Minimal clinically important difference for the S3 Noninvasive Ventilation questionnaire in individuals with COPD using home mechanical ventilation.

Introduction: The S³-Noninvasive Ventilation (S³-NIV) questionnaire is a simple tool that allows monitoring of symptoms and side-effects in individuals using home mechanical ventilation (HMV). Its longitudinal use in monitorisation is complicated by the current absence of a minimal clinically important difference (MCID), which could facilitate the application of a more tailored follow-up and therapy optimisation. We aimed to establish the MCID for the S³-NIV in people with COPD under HMV.

Methods: We conducted an observational study with adult individuals with COPD treated with HMV, followed in an HMV outpatient clinic. The S³-NIV, the Severe Respiratory Insufficiency (SRI) questionnaire and the St George's Respiratory Questionnaire (SGRQ) were applied at baseline and after a 6-month period. Demographic and clinical data were collected from hospital records. The MCID was computed using both distribution- and anchor-based methods. The pooled MCID was computed using the weighted mean (two-thirds anchor- and one-third distribution-based methods).

Results: A total of 99 participants (71% male) were included, with a mean±sd age of 72±9 years and a median (interquartile range (IQR)) forced expiratory volume in 1 s of 37 (29-49)% predicted. Median time under HMV was 40 (IQR 24-84) months. The SRI (r=0.311, p=0.002) and the SGRQ (r= -0.334, p=0.001) questionnaires were correlated with S³-NIV, and therefore were used as anchors. Our pooled analysis resulted in a MCID of 0.8 points.

Conclusion: A MCID of 0.8 points in the S³-NIV questionnaire is proposed in stable individuals with COPD using HMV, supporting the identification of clinically significant changes and management improvement.