Electroencephalographic correlation dimension changes with depth of halothane

ABSTRACT

This study was designed to evaluate the efficacy of dynamic parameters, such as correlation dimension D2, 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 D2 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, D2 on the parietal cortex had a better correlation with the movement. The level of deviation and variation of standardized D2, MPF, and betaL were significant (p MPF > D2. The correlation dimension serves as a better index for the depth of halothane anesthesia defined in forms of a response to external stimulation.