Assessment of depth of general anesthesia - Observations on processed EEG and spectral edge frequency

The daily use of muscle relaxants and the lack of correlation between the hemodynamic behavior and stages of general anesthesia represent the main obstacles in defining the level of cortical activity depression by the anesthetic drugs. Since classical EEG is cumbersome in the operating room, and demands special knowledge, computerized methods of EEG wave analysis have more or less replaced the 'raw' display of the electrical activity of CNS. The paper describes the place of spectral edge frequency (SEF), one of the parameters obtained by processing the EEG waves, in the list of variables which could be monitored during general anesthesia. Besides, our preliminary observations on a combination of mean blood pressure variations and SEF value are presented. In fact, we designed a hypothetical matrix of those two parameters, which seems to be a useful tool for guiding the general anesthesia. SEF kept in a pre-established range (usually 8-12 Hz) seems to be linked with a more evident hemo-dynamic stability. Some data also suggested that a stable SEF on that range contributed to a higher degree of immediate postoperative analgesia after Cesarean section. The limits of SEF oblige the scientists to go on looking for other monitored parameters, to be studied in correlation with processed EEG. Further studies are needed, in order to improve the anesthesiologist's capabilities to define correctly the stage of general anesthesia.