Tracheal intubation in operating room for patients at risk of difficult intubation remains a critical event. The aim of this study is to determine whether Nasal High Flow Therapy by nasal cannula Optiflow® administered before and during intubation is more efficient than the standard care for pre-oxygenation and oxygenation during anticipated difficult intubation

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 = 1) before and during intubation. The device will be maintained in place throughout the intubation procedure (including fiber-optic or laryngoscopic) in order to achieve oxygenation.
• Or Standard Preoxygenation during 4 minutes with FIBROXY® (Fiber-optic intubation) or standard facial mask (Laryngoscopic intubation), at FiO2=100%. FIBROXY mask will be maintained in place during the fiberoptic procedure. Standard facial mask, will be removed after the crash induction.

Inclusion Criteria:

• Patients 18 years of aged and over
• And anticipated difficult intubation
• And requiring a rapid sequence induction for laryngoscopic intubation
• Or requiring a fiberoptic intubation

Exclusion Criteria:

• BMI > 35
• Pulse oxymetry < 90% in ambient air
• Haemodynamic instability
• Pregnancy
• Protected adult
• Lack of consent
• Patient already enrolled in another randomized study looking forward improving preoxygenation quality.