Closed-Loop O2 Use During High Flow Oxygen Treatment of Critical Care Adult Patients (CLOUDHFOT)

Inclusion Criteria: * Patient admitted to the ER * Requiring NHFO * Requiring FiO2 ≥ 30% to keep SpO2 in the target ranges defined by the clinician * Aged over 18 years * Written informed consent signed and dated by the patient or one relative in case that the patient is unable to consent, after full explanation of the study by the investigator and prior to study participation * In case that the consent is given by the relative, patient consent will be requested as soon as the patient will be able to provide informed written consent Exclusion Criteria: Patients who fulfil any of the following exclusion criteria are not eligible for study participation: * Patient with indication for immediate CPAP, NIV, or invasive mechanical ventilation * Hemodynamic instability defined as a need of continuous infusion of epinephrine or norepinephrine \> 1 mg/h * Low quality on the SpO2 measurement using finger and ear sensor (quality index below 60% on the Massimo SpO2 sensor, which is displayed by a red or orange color bar) * Severe acidosis (pH ≤ 7.30) * Pregnant woman * Patients deemed at high risk for need of mechanical ventilation within the next 12 hours * Chronic or acute dyshemoglobinemia: methemoglobin, CO poisoning, sickle cell disease * Tracheotomized patient * Formalized ethical decision to withhold or withdraw life support * Patient under guardianship * Patient deprived of liberties * Patient included in another interventional research study under consent * Patient already enrolled in the present study in a previous episode of acute respiratory failure Post enrollment exclusion criteria * Apparition of a persistent low quality SpO2 signal * Need for an emergent intubation * Discharge from ER