Total intra-venous anesthesia can be provided using a closed-loop system guided by the bispectral index. The purpose of this study is to determine if myorelaxation modifies its functioning.

Inclusion Criteria:

• patients scheduled for a surgical procedure which not require a myorelaxation

Exclusion Criteria:

• age less than 18 years,
• ASA III and above,
• pregnant woman
• combined general and regional anesthesia,
• history of prolonged myorelaxation due to a decrease in cholinesterase,
• patient with a known lack in cholinesterase,
• history of cerebral or psychiatric central,
• allergy to latex, propofol, remifentanil, morphine, muscle relaxant or any of the excipients,
• known hypersensitivity to remifentanil or to an other derivative of fentanyl,
• presence of a pacemaker,
• psychotropic or agonist-antagonist morphine treatment,
• planned post-operative sedation.