A system and method is used for determining from EEG signals the lack of awareness and the depth of anesthesia of a patient to whom an anesthetic agent is being administered. In particular, a log-log representation of the EEG power spectrum of a current patient is compared to another log-log spectrum of a patient in a known condition. By comparison the awareness or depth of anesthesia of the current patient can be determined. The reference spectrum can be an average spectrum of many patients or a previously acquired spectrum of the current patient, or any other spectrum that can be statistically correlated with the current patients spectrum.
