The goal of this observational study is to evaluate whether the airway occlusion pressure recorded during a sudden end-expiratory breath-hold (ΔPocc) is correlated with esophageal swing in pressure and the reliability of P0.1, driving pressure, plateau pressure, pressure-muscle index, and diaphragm ultrasound as noninvasive estimates of inspiratory effort and lung distension in hypoxemic patients undergoing NIV.

The main questions this trial aims to answer are:

- Primary Outcome: whether the airway occlusion pressure recorded during a sudden end-expiratory breath-hold (ΔPocc) is correlated with esophageal swing in pressure and the reliability of various noninvasive estimates of inspiratory effort and lung distension in hypoxemic patients undergoing NIV.

Secondary outcomes will include:

• Statistic metric of association between P0.1, ΔP, PMI and ΔPes
• Statistic metric of association between P0.1, ΔPocc, ΔP, PMI and PaO2/FiO2 ratio
• Statistic metric of association between P0.1, ΔPocc, ΔP, PMI and tidal volume
• Statistic metric of association between P0.1, ΔPocc, ΔP, PMI and DTF%
• Statistic metric of association between P0.1, ΔPocc, ΔP, PMI and Ex/DTF%
• Statistic metric of association between P0.1, ΔPocc, ΔP, PMI and respiratory rate, VAS dyspnea and VAS discomfort.

Participants will undergo the following tasks and treatments:

• Complete written informed consent before enrollment.
• Post-extubation noninvasive ventilation via nose-to-mouth and full-face masks.
• Monitoring of esophageal pressure (in all patients the catheter will be placed before extubation, according to clinical judgment, and its correct position will be verified through a positive pressure occlusion test)
• Continuous recording of airway pressure, flow, and esophageal pressure (Pes), using a dedicated pneumotachograph and pressure transducer.
• Sudden end-inspiratory and end-expiratory occlusion maneuvers, to measure plateau pressure (Pplat) and end-expiratory airway occlusion pressure (ΔPocc), respectively.
• Collection of hemodynamic and arterial blood-gas parameters, performed according to clinical judgment, along with assessments of dyspnea and discomfort using a modified visual analogue scale (VAS).
• Diaphragm ultrasound during occlusion maneuvers, measuring diaphragm displacement, diaphragm thickening fraction (DTF%), and diaphragmatic excursion (Ex) under various conditions.

Inclusion Criteria:

• Age greater than or equal to 18 years.
• Non-pregnant and non-lactating.
• Monitored through esophageal pressure for clinical decision before extubation.
• Able to provide written informed consent to participate in the study.

Exclusion Criteria:

• Patients with severe facial trauma or deformity that precludes the placement of a facemask or esophageal catheter.
• Patients with neuromuscular disorders that may impair inspiratory drive and effort.
• Patients with acute exacerbation of COPD
• Patients with esophageal or tracheal abnormalities that impede esophageal manometry.
• Patients with a known hypersensitivity or allergy to any of the materials used in the study.
• Excessive air leak (difference between inspiratory and expiratory tidal volume major or equal to 30% [prot. n 1136947]).

All hypoxemic patients with a PaO2/FiO2 ratio equal or lower than 300, receiving post-extubation noninvasive ventilation via an nose-to-mouth or a full-face mask, will be screened for eligibility.