Intraoperative EEG monitoring: (I). Parametric representation of processed EEG during anesthesia.

One of the most common techniques of EEG monitoring during operations is to produce a three dimensional image by displaying the frequency distributions with respect to time as in compressed spectral array (CSA) and density-modulated spectral array (DSA). In order to characterize these images by numerical parameters, we defined two parameters; the percent spectral edge frequency as the frequency at which the one-sided-power sum reaches the designated percentage of the total; and the mean frequency as the power-weighted mean within the interval that includes a dominant spectrum in the frequency distribution. These parameters were superimposed on displays to characterize EEG changes, and they proved to be a very powerful tool to quantitate variations in data among anesthetic techniques and thus efficiently control the depth and duration of anesthesia. We report a number of actual cases.