The Global Usability Score Short-Form for the simplified assessment of dry powder inhalers (DPIs) usability.

Abstract

BackgroundThe choice of the Dry Powder Inhaler (DPI) to prescribe is a critical issue. The estimation of DPIs usability depends on the objective assessment of several indices related to both subjective and objective determinants. The Global Usability Score (GUS) Questionnaire is a comprehensive tool usable for checking, comparing, and ranking inhalers’ usability objectively in real life, but it takes some time to fill.AimThe aim of this study was to favour the quicker check of DPIs usability in clinical practice by means of a simplified short-form GUS (S-GUS) Questionnaire, while maintaining the high specificity and sensitivity of the original, extended version of the Questionnaire (O-GUS questionnaire).MethodsThe usability of the six most prescribed DPIs was assessed in 222 patients with persistent airway obstruction and needing long-term inhalation treatments. LASSO regression and multicollinearity test were used to select the subset of questions of the O-GUS questionnaire, with the highest information power. Each item was then scored using the corresponding coefficient in the linear regression (normalized at 50 as the O-GUS score). Agreement between the original and the short-form questionnaire was evaluated using the Cohen’s kappa statistic (κ). The overall S-GUS values obtained for each DPI were then compared to those from the O-GUS, in the same patients, using a Bayesian indirect comparison (IC) model.ResultsAfter the statistical selection of the items mostly contributing to the overall score, the novel S-GUS questionnaire consists of twelve items only. Nine items are related to patients’ opinion before DPIs handling, and three to the nurse’s assessment after DPIs practicality. O-GUS and S-GUS score were strongly correlated (R2=0.9843, p<0.0001) and the usability score calculated for each DPI by means of the O- and of S- GUS overlapped almost completely (κ=84.5%, 95% CI 81.3% to 89.2%). Furthermore, S-GUS was much faster to complete than O-GUS (mean time 6.1 vs 23.4 minutes, p<0.001). Estimates of S-GUS, obtained from the IC model, allowed to propose a simple classification of usability: “good” by GUS values >25; “pretty good” by values ≤25≥15, and “insufficient” by values <15.ConclusionsThe S-GUS proves as much specific and suitable as the extended O-GUS questionnaire in measuring DPIs usability, while maintaining the same high sensitivity. As the time required for its use is quite shorter, S-GUS is also particularly suitable and helpful in current clinical practice.