Neurophysiological basis of EEG interpretation appears to day stil poor; conversely mathematical and computerized management of EEG waveform is well documented. To quantify the signal two main procedures are now used: spectral analysis of frequency and aperiodic analysis. As for others electro-biological signals, to-day micro-computers facilities for exemple colored in prospect screen presentation, picture or EEG call back, data record and printing...allows such a management easy to read by anyone in real time and into operating room or intensive care unit conditions. Such possibilities are now the main point of EEG monitoring because it appears as an empiric clinical practice. The knoledge of genuine activity of anesthesic drugs on neuron and neurologia metabolism, local cerebral blood flow and/or neuromediators concentration is not wider than EEG neurophysiological basis. So that, more than the EEG signal itself, alterations of its stability allows specific monitoring for anesthesia which could be more beneficial than others to day usual.