This prospective monocentric phamacokinetics study aims to compare plasmatic concentrations of Propofol and Remifentanil required to target a specific range of monitored anesthesia and analgesia during sus-mesocolic surgery in obese and non obese patients.

Remifentanil and Propofol are administered intravenously as an opioid pain reliever and hypnotic pain reliever during anesthesia. Their advantages are numerous: short half-life allowing anesthesia and rapid awakening, little accumulation, allowing to adapt the level of anesthesia or sedation to each patient, few side effects.

Entropy° is an index derived from the electroencephalographic signal of patients, validated for the evaluation of the level of narcosis during general anesthesia.

ANI ° (nociception index analgesia) is an index using the ventilatory physiological variability of the sinus rhythm validated to monitor patient's analgesia during general anesthesia.

These non-invasive means of analgesia and sedation monitoring allows the clinician to ensure satisfactory levels of anesthesia by administering products at minimum effective doses.

The authors propose to determine whether, for a comparable target effect (analgesia and monitored sedation), plasmatic concentrations and administration rates of propofol and remifentanil necessary during general anesthesia for a comparable surgical stimulus are the same in populations of obese and non obese patients.

Inclusion Criteria:

Obese patients group:

• Age ≥ 18 years old
• Severe and morbidly obese patients (35kg / m2≤IMC <55kg / m2).
• Patients undergoing general anesthesia for laparoscopic susmesocolic surgery (bariatric surgery or cholecystectomy).
• Patients who have given their consent in the manner described by the public health law of August 9, 2004.
• Patients benefiting from a Social Security scheme.

Group of non-obese patients:

• Age ≥ 18 years old
• Patients with normal weight or slightly overweight (19 \