A system comprising means for obtaining a signal representative of the electrocortical activity of the patient, means for analyzing this signal in order to derive from it a signal of depth of anaesthesia, means for monitoring the value and development over time of this signal of depth of anaesthesia, these means being associated with means for calculation of control commands of the injection means, in order to regulate automatically in closed loop the signal of depth of anaesthesia in a predetermined range around a target value, and in that the means for injection of anaesthetics comprise first means for injection of a hypnotic that receive control commands at a first frequency, and second means for injection of a morphinomimetic that receive control commands at a second frequency higher than the first frequency.
