Obesity is increasing in France, resulting in an increased demand for bariatric surgery. However obesity also alters physiopathological pathways and the pharmacokinetics of anesthestic agents. The investigators objective is to compare, among morbidly obese patients, the immediate and intermediary emergence kinetics after balanced anesthesia using remifentanil associated either with desflurane (reference arm) or with xenon (experimental arm).

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) I to III
• requires bariatric surgery
• body mass index (BMI) >= 35 kg/m2
• patient speaks and writes French
• patient has signed consent form
• patient enrolled in a social security program

Exclusion Criteria:

• patient refuses to sign consent
• ASA IV or more
• patient is pregnant or breastfeeding
• history of hyperthermy (or suspicion, or family history thereof)
• history of liver disease, icterus, unexplained fever, or eosinophilia after administration of a halogen anesthesia
• patient has symptomatic gastro-oesophagean reflux
• patient has hypersensitivity to one or more of the following substances: propofol, remifentanil, celocurine, cisatracurium, rocuronium, desflurane, xenon, paracetamol, ketoprofen, nefopam, tramadol
• patient has obstructive respiratory failure (chronic obstruction pneumopathy, asthma) or has heart disease with severly altered cardiac function
• patient has high intracranial pressure
• patient requires high concentrations of oxygen (fio2>40%)
• patient has a neuro-sensorial deficient which prevents reading, writing, or response to simple oral commands (severe deafness, language impairment...)in the absence of a prothesis
• patient has a psychiatric pathology, or chronically consumes alcohol or other mind-altering substance
• patient has had general anesthesia in the last 15 days
• patient under guardianship
• impossible to correctly communicate information to the patient
• absence of efficient contraception for women of childbearing age
• participation in another study within the last 3 months