Occlusion pressure at 100 ms (P0.1) is a reliable and non-invasive index of inspiratory drive that can be measured easily on most ventilator. Unfortunately, P0.1 cannot be measured reliably in non-intubated patients. In those receiving non-invasive ventilation, the measurement of P0.1 might be inaccurate due to leaks. P0.1 cannot be measured at all in patients receiving high-flow nasal canulae (HFNC).

Ultrasound indices of diaphragm contractile function, namely diaphragm excursion, velocity and thickening fraction, could be reliable and non-invasive proxies of respiratory drive in non-intubated patient.

Our hypothesis is that ultrasound indices of diaphragm function may reliably estimate P0.1. To validate this hypothesis, theses indices will be measured simultaneously with P0.1 in intubated patients, during diaphragm loading conditions similar to spontaneous breathing: the spontaneous breathing trial (SBT). The SBT is used to evaluate if patients can breathe without the assistance provided by the ventilator, and thus, be weaned from mechanical ventilation.

Inclusion Criteria:

• - Age ≥ 18 years old
• Patient intubated or tracheostomized
• Decision by the clinician in charge to initiate a SBT
• After information, the patient or next of kind did not refuse to participate (according to the French law, written informed consent is waived)

Exclusion Criteria:

• - Suspicion of diaphragmatic nerves injury
• Preexisting neuromuscular disease
• Spinal cord injury above C5
• Neuromuscular blockade within last 24 hours
• Body mass index > 40 kg/m2
• Pregnancy or breast feeding
• Patient under legal protection

Patients admitted to the intensive care unit who are intubated or have undergone a tracheostomy.

The procedures carried out with the French data privacy authority (CNIL, Commission nationale de l'informatique et des libertés) do not provide for the transmission of the database, nor do the information and consent documents signed by the patients.

Consultation by the editorial board or interested researchers of individual participant data that underlie the results reported in the article after deidentification may nevertheless be considered, subject to prior determination of the terms and conditions of such consultation and in respect for compliance with the applicable regulations.

Beginning 3 months and ending 3 years following article publication. Requests out of these time frame can also be submitted to the sponsor

Researchers who provide a methodologically sound proposal.