Intravenous lidocaine is efficient for management of post operative pain in abdominal surgery. As previously published in literature the investigators use it during bariatric surgery.

Nevertheless plasmatic concentration of lidocaine is unknown in this population, despite a widespread use.

Investigators propose in this work to bring an objective proof that administration of lidocaine based on a modified body weight is safe.

Intravenous administration concerned the peri operative period. A total of six samples are taken for each patient.

Investigators get approbation of local ethic committee for this work.

Inclusion Criteria:

• Adult who perform a bariatric surgery (sleeve, by-pass, mini by-pass) under laparoscopy
• Body mass index > = 40 kg/m2
• Informed consent signed
• Patient treated with intravenous administration of lidocaine

Exclusion Criteria:

• Contraindication to lidocaine use (allergy, atrioventricular block, seizure, porphyria)
• Concomitant use of beta blocker and others anti arrhythmic drugs
• Cardiac or hepatic insufficiency
• Pregnancy