Electroencephalogram was analyzed automatically by measurement of burst suppression ratio and asymmetry index and by Fast Fourier Transform to calculate total absolute spectral power ; relative spectral power in the ( 0.5-3 .5 Hz ) , ( 4-7 .5 Hz ) , ( 8-12 .5 Hz ) , and ( 13-30 Hz ) frequency bands ; spectral edge frequency ; and mean dominant frequency .