Evaluation of EEG β2 / θ -ratio and channel locations in measuring anesthesia depth

In this paper, the ratio of powers in the frequency bands of β2 and θ waves in EEG signals (termed as the β2 /θ -ratio) was introduced as a potential enhancement in measuring anesthesia depth. The β2 / θ -ratio was compared to the relative β -ratio which had been commercially used in the BIS monitor.Sensitivity and reliability of the β2 / θ -ratio and EEG measurement locations were analyzed for their effectiveness in measuring anesthesia depth during different stages of propofol induced anesthesia (awake, induction, maintenance, and emergence). The analysis indicate that 1) the relative β -ratio and β2 / θ -ratio derived from the prefrontal, frontal, and the central cortex EEG signals were of substantial sensitivity for capturing anesthesia depth changes. 2) Certain channel positions in the frontal part of the cortex, such as,F4 had the combined benefits of substantial sensitivity and noise resistance. 3) The β2 / θ-ratio captured the initial excitation, while the relative β -ratio did not. 4) In the maintenance and emergence stages, the β2 /θ -ratio showed improved reliability. Implications: The ratio of powers in EEG frequency bands β2 and θ derived from the frontal cortex EEG channels has combined benefits of substantial sensitivity and noise resistance in measuring anesthesia depth.