The passage of air through the nasal cavity generates rhythmic oscillations transmitted by the olfactory bulb to the brain, which induces cerebral activation in functional areas and is associated with better cognitive performance compared to oral breathing. Consequently, the abolition of nasal ventilation in patients intubated via the orotracheal route could have deleterious effects on brain activity. Besides the loss of olfaction, the abolition of nasal ventilation could affect brain activity and respiratory control, consequently altering regional pulmonary ventilation.

The hypothesis of the study is that nasal ventilation through the passage of humidified nasal airflow in patients intubated via the orotracheal route would be associated with modulation of cerebral electrical activity and tissue oxygenation and a modification of regional pulmonary ventilation.

The effects of nasal ventilation on cerebral activity will be studied on orally intubated and sedated patients in six experimental conditions. The first condition consists of nociceptive stimulation of the left upper limb as a negative control. In three conditions, the inspired fraction of oxygen (FiO2) will remain at 21% while applying three different rates of humidified nasal air at 0L/min, 30L/min and 60L/min respectively. The last two conditions consist of applying humidified nasal air at 30L/min and 60L/min with a FiO2 of 100%. The primary objective of this study is to evaluate the effects of high-flow humidified nasal air on electroencephalogram activity (root mean square gamma frequency) in sedated, orally intubated patients. The secondary objectives of the study are to evaluate the effects of high-flow humidified nasal air on cerebral perfusion and oxygenation, gas exchange and regional pulmonary ventilation in the same patients.

Inclusion Criteria:

1. Age ≥ 18 years old
2. Hypoxemic acute respiratory failure
3. Intubation and mechanical ventilation since less than 4 days
4. PaO2/FiO2 ratio less than 200
5. RASS<-4
6. Consent obtained from next of kin
7. Patient with health insurance

Exclusion Criteria:

1. Central nervous system diseases (stroke, MS, epilepsy)
2. Psychiatric illnesses (psychosis, depression) (indicated on patient's medical record)
3. Hemodynamic instability (noradrenalin>2mg/h)
4. Patient on AME
5. Patients under legal protection (guardianship/curators)
6. Pregnant or breast-feeding women

The study population will be adult patients with acute respiratory failure who are orally intubated and sedated. These patients should be free of neurological and psychiatric diseases prior to ICU admission. The choice of this particular population is justified by its exposure to mechanical ventilation and continuous sedation, which are recognized risk factors for brain damage.

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.