Chronic obstructive pulmonary disease (COPD) management involves pharmacologic therapy delivered via inhalers. Choosing the right inhaler can be challenging. The In-Check Dial G16®, designed as a training device, helps clinicians assess inspiratory capacity by simulating inhaler resistance but can be time-consuming. Spirometry quantitatively assesses lung function and is essential for COPD diagnosis. This study explores spirometry as a predictive tool for assessing the inspiratory flow required for dry powder inhalers (DPI).

We included COPD patients using inhalers for at least one month who underwent spirometry in two Portuguese hospitals. On the same day, patients' inhalatory capacity was evaluated with the In-Check DIAL G16®. Patients were considered able to use the DPI if they could achieve a flow higher than 30 L/min at least three times at the R3 resistance level.

Ninety-one patients enrolled, most using pressurized metered-dose inhaler/soft mist inhalers (37.4 %), low resistance (30.8 %), medium-low resistance (23.1 %), and medium resistance (8.8 %) inhalers. Peak inspiratory flow (PIF) best predicted DPI use, with a cut-off value of 3.10 L/s providing 69.2 % sensitivity and 76.9 % specificity. Forced inspiratory flow at 50% of FVC (FIF₅₀) was the second-best predictor, with a cut-off value of 2.91 L/s, 63.7 % sensitivity, and 69.2 % specificity.

PIF's strong correlation with inhalation capacity underlines spirometry's importance in COPD evaluations. Identified PIF and FIF₅₀ cut-off values assist clinicians in selecting appropriate inhalers. Spirometry offers a more accessible and time-efficient alternative to the In-Check Dial G16®, warranting further research to validate these findings and integrate spirometry-based assessments into COPD management.