PURPOSE: Effective treatment of chronic obstructive pulmonary disease (COPD) primarily relies on treatment delivered through inhaler devices. The effectiveness of dry powder inhalers is compromised by insufficient peak inspiratory flow (PIF). Understanding the evolution of PIF during hospitalization is crucial for optimizing inhaler selection and improving patient outcomes. PATIENTS AND METHODS: A prospective monocentric observational study was conducted at Fribourg Hospital, Switzerland, from August 2022 to December 2022. PIF was assessed at hospital admission and discharge in all patients with COPD admitted to the internal medicine division. The primary outcome was the evolution of maximum PIF at a fixed medium-low resistance (R2) during hospitalization. Secondary outcomes included the variation of PIF in the intra-assessment evaluation and transitioning between sufficient and insufficient PIF. RESULTS: Forty-nine patients were enrolled, 61% were men and 65% experienced an acute COPD exacerbation (AECOPD). The maximum PIF for R2 increased from 64.8 ± 17.2 L/min at admission to 70.7 ± 17.9 L/min at discharge, showing a 5.9 L/min improvement (95% CI: 2.4-9.5, p < 0.01). A hospitalization >5 days in patients hospitalized for an AECOPD is associated with a higher increase in PIF (p < 0.05). In the intra-assessment measurement, we observed an increase in PIF in the successive measurements (p < 0.01). CONCLUSION: Hospitalized patients with COPD experienced a significant increase in PIF during their stay. These results appear to be independent of the reason for hospitalization but need to be confirmed with a larger sample. Nevertheless, these findings underscore the importance of regular PIF assessment and influence inhaler selection.