Tracheal intubation, particularly before surgery, is traditionally done in supine position. It was shown in the general population and in obese patients in particular, that the pre-oxygenation in a 25° head-up position provided a better efficiency of the pre-oxygenation and an apnea time longer. This position would also allow for better intubation conditions in direct laryngoscopy.

The investigators intend to assess two different patient's intubation position : supine position and 25° head-up position

Randomization assigned in random block, stratification by operator (20 patients per operator, 10 in each group).

Interim analysis every 100 patients.

Inclusion Criteria:

• - patients scheduled for various surgeries requiring general anesthesia with curare, with intubation of the trachea, eligible for intubation by direct laryngoscopy.
• > 18 years
• patients with social security

Exclusion Criteria:

• Emergency surgery.
• Patient who requiring rapid sequence induction.
• Intubation without curare.
• Expected difficult intubation with planned modification of the intubation protocol (i. e. intubation under fibroscopy, airtrach or videolaryngoscopy)
• Patient with a history of epilepsy, pulmonary or cardiovascular disease (including ischemic heart disease, symptomatic asthma or obstructive pulmonary disease).
• Patient with mask phobia.
• BMI> 30kg / m2
• Patient who are refusing to take part.
• Patient protected major, minor, pregnant women, patients deemed incapable of giving informed consent.

No masking