Power analysis of gamma frequencies (30 - 47Hz), adjusting for muscle activity (80 - 97Hz), in anesthesia: a comparison between young adults, middle-aged and the elderly.

This study looks at the role of EEG gamma activity, and the influence of facial EMG (80-97 Hz), in predicting consciousness during anesthesia. It also studies the association between the conventional depth of anesthesia index, BIS (Aspect Medical Systems), and EEG gamma and EMG activity. Data has been collected from 21 adult patients and grouped into young adults (18 - 39 yrs, n=3), middle-aged (40 - 64 yrs, n=10) and the elderly (65+ yrs, n=8). The power of the EEG gamma activity was recorded from Fpz - Mastoid and the power of the EMG was recorded from Fpz - Mastoid and Masseter - Mastoid. It has been found that when considered alone, EEG gamma power is associated with both BIS index and consciousness versus unconsciousness, showing a decrease in power as consciousness is lost. When the effect of EEG gamma power is adjusted for EMG, it is found that generally these associations can be explained by the EMG power alone. There are two exceptions to this. In the young adults group there is a stronger association between BIS index and EEG gamma than there is between BIS index and EMG. In the elderly group, the state of consciousness is equally associated with EEG gamma and EMG recorded from the Masseter, but not with the EMG recorded from Fpz.