Oro-tracheal intubation in operating room in obese patients with BMI > 35kg/m2 remains a critical event. The aim of this study is to determine whether Nasal High Flow Therapy by nasal cannula Optiflow® is more efficient than the BIPAP preoxygenation before orotracheal intubation after crash induction in obese patients

This study will be designed as followed : Patients will be randomized in 2 groups :

• Preoxygenation during 4 minutes with High Flow Nasal Cannula (60l/min FiO2 (fraction of inspired oxygen) = 1) before orotracheal intubation after crash induction. The device will be maintained in place throughout the intubation procedure in order to achieve apnoeic oxygenation.
• Or Preoxygenation during 4 minutes with Bi-level Positive Airway Pressure (BIPAP) with Expiratory Positive Airway Pressure (EPAP) + 5 cm H2O and Inspiratory Airway Positive Airway Pressure (IPAP) + 15, meaning a 10cm H2O pressure support. The facial mask with be removed after before crash induction enabling laryngoscopic vision.

Inclusion Criteria:

• Obese patient with BMI > 35kg/m2
• Age between 18 and 80 years
• Requiring a crash induction sequence for oro-tracheal intubation.

Exclusion Criteria:

• Pulse oxymetry < 90% in ambient air
• Haemodynamic instability
• Burned patient
• Indication of intubation vigil in spontaneous ventilation
• Patients with a documented Cormack IV exposition before inclusion
• Protected adult
• Pregnancy
• Lack of consent
• Patient already enrolled in an other randomized study looking forward improving preoxygenation quality.
• Lack of French social protection