Inclusion Criteria:  Patients undergoing general anesthesia, with invasive mechanical ventilation including an airway device (supraglottic airway device or tracheal tube) at their arrival in PACU. ASA physical status classification 1, 2, or 3 stabilized. Surgery performed in emergency operating room department including vascular, digestive, urological and minor trauma surgery or surgery performed in head and neck anesthesia pole block including anterior cervical spine, lumbar disc herniation, cranioplasty, nerve stimulator, vertebroplasty, narrow lumbar canal, simple arthrodesis (less than or equal to two stages), otological, ophthalmological and skin surgery.  Exclusion Criteria:  Per-operative hemodynamic instability. Patients with a BMI greater than 35. Patients classified as difficult to intubate and / or ventilate. Heavy surgeries (operating time greater than 4 hours). Patient requiring postoperative non invasive mechanical ventilation Patients with diagnosed COPD SPO2 in room air < 96% before the intervention. Any patient under guardianship. Pre-operative and / or intra-operative morphine intake. Surgical management of the upper airways (ex : tonsillectomy) Pregnant and lactating women.