Impact of End-tidal Oxygen Monitoring During Preoxygenation Before Intubation for Acute Hypoxemic Respiratory Failure in ICU Setting

Inclusion Criteria: * Admitted in ICU * In AHRF, defined as : respiratory rate greater than 25 breaths per minute or signs of respiratory distress, and a partial pressure of oxygen (PaO2) to FiO2 ratio equal to or below 200 mmHg (calculation of estimated FiO2 under standard oxygen as follows: FiO2 = 0.21 + oxygen flow rate × 0.03). * Indication to intubate based on physician judgment * Written consent obtained from the patient, relative, or emergency consent. Exclusion Criteria: * Contraindications to NIV (recent laryngeal, oesophageal, or gastric surgery, and substantial facial fractures) * Severe haemodynamic failure (Norepinephrine ≥ 0.3 μg/kg/min to maintain MAP ≥ 65 mmHg) or cardiac arrest * Do not intubate order * Pregnancy * breastfeeding * Refusal to participate