INTRODUCTION: Right diaphragmatic excursion is a reliable and reproducible technique used in intensive care to assess diaphragmatic function. The aim of this study was to investigate the relationship between the appearance of diaphragmatic motion and the etiological diagnosis of patients admitted to the emergency department with acute respiratory failure (ARF). MATERIALS: A prospective, observational, and multicenter pilot study was conducted. All adult patients admitted in the emergency department with ARF were included. The different visual patterns of diaphragmatic motion were analyzed according to the three main etiologies of ARF encountered in emergency departments. RESULTS: A total of 39 adult patients were included. We observed a different visual pattern in patients with pneumonia. A sum of plateau times of less than 0.2 s predicted that the main diagnosis was pneumonia, with sensitivity = 89% 95%CI [52%
100%], specificity = 87% 95%CI [69%
96%]. CONCLUSION: Our study seems to show that the shape of diaphragmatic motion in patients with ARF secondary to pneumonia is different from that in patients with exacerbation of chronic obstructive pulmonary disease or acute heart failure. TRIAL REGISTRATION: ClinicalTrials.gov: NCT04591509.