Inclusion Criteria:  Patients managed by the Anesthesia Department of the Foch Hospital; Anesthetic sedation (analgesia with remifentanil) or general anesthesia (combining remifentanil, propofol and possibly rocuronium); Men or women over 18 and under 80 years of age; To benefit from a surgical intervention scheduled > 48 hours in relation to the procedure; Scheduled outpatient surgery; Have signed a consent form; Be affiliated to a health insurance plan.  Exclusion Criteria:  Pregnant or nursing patients; Oxygen dependent preoperatively or at risk of oxygen dependence postoperatively; Lung resection surgery; Brain surgery (intracerebral neurosurgery); ENT surgery requiring a half-seated position after the operation; Being deprived of liberty or under guardianship.