Although non-invasive mechanical ventilation (NIV) is the gold standard treatment for patients with acute exacerbation of COPD (AECOPD) who develop respiratory acidosis, failure rate are still high ranging from 5% to 40%. Recent studies have shown that the onset of severe diaphragmatic dysfunction (DD) during AECOPD increases risk of NIV failure and mortality in this subset of patients. Although the imbalance between the load and the contractile capacity of inspiratory muscles seems the main cause of AECOPD-induced hypercapnic respiratory failure, data regarding the influence of mechanical derangement on diaphragmatic performance in this acute phase are lacking. With this study we aim at investigating the impact of respiratory mechanics on diaphragm function in AECOPD patients who experienced NIV failure. AECOPD with respiratory acidosis admitted to the ICU of the University Hospital of Modena from 2017-2018 undergoing mechanical ventilation (MV) due to NIV failure were enrolled. The study protocol consisted of two consecutive phases; in the first step measurements of static respiratory mechanics and end expiratory lung volume (EELV) were performed after 30 minutes of MV in volume control mode. In the second step transdiaphragmatic pressure (Pdi) was calculated by means of a sniff maneuver (Maximal Pdi) after 30 minutes of spontaneous breathing trial. Linear regression analysis and Pearson's correlation coefficient was used to asses the association between Maximal Pdi values and static and dynamic mechanical features and the association between Maximal Pdi and Pdi/Maximal Pdi.

Inclusion Criteria:

• age over 18 years
• AECOPD with respiratory acidosis admitted to the Respiratory Intensive Care Unit of the University Hospital of Modena (Italy) undergoing endotracheal intubation due to NIV failure.

Exclusion Criteria:

• history of neuromuscular disease,
• presence of chest wall deformities,
• coexistence of interstitial lung disease,
• presence of pulmonary edema,
• severe hemodynamic instability,
• septic shock,
• evidence of lobar pneumonia or bilateral parenchymal consolidation at chest X-ray on admission,
• contraindication to NIV,
• previously assessed diaphragmatic palsy,
• intracranial hypertension,
• known pregnancy,
• need for immediate endotracheal intubation,
• neurologic impairment,
• lack of collaboration,
• unreliable maneuver to calculate maximal transdiaphragmatic pressure.

Cohort study