• Global score (calculated parameter which depicts the performance of the system, i.e. its capacity to maintain BIS in the desired range)
  

• consumption of propofol and remifentanil during the induction and the maintenance of the anaesthesia
  
• number of modifications of target of propofol and remifentanil
  
• number of episodes of hemodynamic anomalies having required a treatment
  
• intraoperative volume loading and transfusion
  
• extubation time, explicit memorisation
  
• dysfunctions of each system
  

Several monitors are currently proposed to evaluate the depth of hypnosis. Among them, Bispectral Index (BIS) is a well known and widely used parameter derived from the patient’s electroencephalograph (EEG). A closed-loop anesthesia system can be built using BIS as the control variable, a proportional–integral–differential control algorithm, a propofol and a remifentanil target-controlled infusion systems as the control actuators Preliminary results show that this system can be used during surgery. Spectral entropy relies on the extent of disorder in both EEG and electromyography (EMG) signals and returns 2 values: State Entropy (SE) and Response Entropy. SE is computed over the frequency range of 0.8–32 Hz and reflects the level of hypnosis while Response Entropy is computed over the frequency range of 0.8–47 Hz and reflects also EMG activity. BIS and SE are dimensionless numbers scaled from 100 to 0 for BIS and from 91 to 0 for SE. We hypothesized that SE can be used as the control variable. In preparation for a large multi-center control trial, we propose a prospective randomized study to evaluate the effectiveness of such a closed-loop anesthesia system. Two groups of patients are compared: one in which propofol and remifentanil are administered by the anesthesiologist using target-controlled infusion systems, and one in which propofol and remifentanil are administered automatically by the combined closed-loop anesthesia system. In both groups, the goal is to maintain SE between 40 and 60, the recommended range during anesthesia by the manufacturer. We expect the combined closed-loop anesthesia system group to do similar or better.