Electroencephalographic Correlation Dimension Changes with Depth of Halothane

This study was designed to evaluate the efficacy of dynamic parameters, such as correlation dimension $D_2,$ by comparing spectral electroencephalographic (EEG) parameters. These parameters are used to estimate the depth of halothane anesthesia as defined by the presence of body movement in response to a tail clamp. Six rats were used and each of them was exposed to halothane sequentially at the concentrations of 0%, 0.5%, 1.0% and 1.5% for 30 min. A tail clamp was applied every five min and the movements were recorded at each concentration level. The spectral parameters and the dynamic parameters were derived from 20-sec and 10-sec segments, respectively, from the last 5-mins of EEG recording at each concentration level. Correlation coefficients between the parameters and the movements were calculated. Standardized values of three parameters, betaL power, median power frequency (MPF), and $D_2$ were derived by calculation based on the number of animals showing the movement in response to a tail clamp. The betaL power had the largest correlation coefficient to spontaneous movement and to the response to a tail clamp than any other band parameter. MPF had a better correlation with the movement than 90% spectral edge frequency. Among the dynamic parameters, $D_2$ on the parietal cortex had a better correlation with the movement. The level of deviation and variation of standardized $D_2,$ MPF, and betaL were significant (p<0.01). The order of deviation and variation was; betaL power > MPF > $D_2.$ The correlation dimension serves as a better index for the depth of halothane anesthesia defined in forms of a response to external stimulation.