Monitoring the bispectral index (BIS) as a peri-operative hemodynamic tool appears to be justified by the agreement between various clinical situations in which BIS monitoring appears to be of value: the prognosis in traumatic head injury, the diagnosis of brain death , and the diagnosis of amniotic fluid embolism. The current controversy concerning the "triple low" state reinforces the need for an accurate study in this field. Furthermore, the recent review by Bidd argues in this sense.

Inclusion Criteria:

• Adult (over-18) patients presenting an indication for general anaesthesia during elective cardiac surgery and being monitored for sedation depth
• Good echogenicity
• Social security coverage

Exclusion Criteria:

• Pregnancy
• Subjects with black skin (a known technical limitation of plethysmography)
• Cardiac arrhythmia
• Sepsis
• Poor echogenicity
• Legal guardianship or incarceration
• Complications of anaesthesia during induction (anaphylactic shock, cardiac arrest, arrhythmia, or intubation not possible)

patients presenting an indication for general anaesthesia during elective cardiac surgery and being monitored for sedation depth