Modern management of acute respiratory failure aims to relieve dyspnea and anxiety by providing a non-invasive respiratory support. This approach tries to avoid endotracheal intubation, patient self inflicted lung injuries (PSILI) and diaphragmatic dysfunction. The present study aims to evaluate dyspnea, pulmonary regional ventilation and diaphragmatic function in patients with hypoxemic acute respiratory failure by different observations, and to bring risk factor for intubation out.

Patients aged of 18 years or more, presenting with an acute respiratory failure without hypercapnia will be included in the study. Clinical and biological variables, dyspnea assessment, regional lung ventilation (electrical impedance tomography) and diaphragm function (ultrasound) will be evaluated at inclusion and at 2 hours, 4 hours and 48 hours after inclusion. In case of intubation, diaphragmatic function will be also evaluated with phrenic nerve stimulation technique.

Primary endpoint is intubation at day 7. Secondary endpoints are measurement of dyspnea, pulmonary ventilation and diaphragmatic function, also ventilator free days, ICU length of stay and mortality.

Inclusion Criteria:

• Age > 18

• Acute respiratory insufficiency defined by the three following items :

  1. PaO2/ FiO2 <300
  2. Respiratory rate > 25/min
  3. Oxygen support > 10L/min or High Flow nasal oxygen (HFNO)

• Non opposition by the patient to be included

• Social insurance

Exclusion Criteria:

• Respiratory acidosis (pH < 7,35 PaCO2 > 45mmHg or 6kPa)
• Chronic respiratory disease ( COPD, bronchiectasis…)
• Cardiogenic Acute lung oedema
• Non intubation decision at randomisation
• Contraindication for Electro-impedance tomography-belt placement (chest trauma with rib fractures, thoracic wound, chest tube).
• Uncommunicative patient (Glasgow coma scale <12)
• Guardianship or curators for vulnerable patients.

Patients with de novo acute respiratory failure

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.