Monitoring depth of anesthesia through measurement of phase coupling among spontaneous EEG rhythms

Abstract

Awareness during general anesthesia for its serious psychological e ects on patients and some juristically problems for anesthetists has been an important challenge during past decades. Monitoring depth of anesthesia is a fundamental solution to this problem. Induction of anesthesia alter frequency and mean of amplitudes of the electroencephalogram (EEG), and its phase couplings. By increasing the anesthetic drug dose, the mean frequency of the signal decreases and its amplitude increases and theta or delta waves appear. In this study, we analyze EEG changes for phase coupling between delta and alpha sub-bands using a new algorithm for depth of general anesthesia (DOA) measurement based on complex wavelet transform in patients anesthetized through total intravenous anesthesia (TIVA) by Propofol. By taking bispectral index (BIS) values as reference we calculate entropy and histogram of modulated signals.Entropies correspond to di erent BIS intervals using Mann-Whitney U test show that they have di erent continuous distributions. The results demonstrate that there is a phase coupling between 3-4 Hz in delta and 8-9 Hz in alpha sub-bands and these changes are shown better at the channel (T7) of EEG. Moreover, when BIS values increase, the entropy value of modulated signal also increases and vice versa.Measuring phase coupling between delta and alpha sub-bands of EEG signals through Morlet continuous complex wavelet transform analysis reveals the depth of anesthesia level.The method can be used to measure depth of general anesthesia to prevent awareness of the patients during anesthesia.|Keywords : Depth of anesthesia, Awareness, Complex wavelet transform, Modulated Signal, Phase Coupling, EEG Waves, Entropy Measurement.