β /θ -ratio and channel locations in measuring anesthesia depth

In this paper, the ratio of powers in the frequency bands of 2 β and  waves in EEG signals (termed as the 2 β /θ-ratio) was introduced as a potential enhancement in measuring anesthesia depth. The 2 β /θ-ratio was compared to the relative  -ratio which had been commercially used in the BIS monitor. Sensitivity and reliability of the 2 β /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 indicated that 1) the relative  -ratio and 2 β /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 , had the combined benefits of substantial sensitivity and noise resistance. 3) The F4 2 β /θ-ratio captured the initial excitation, while the relative  -ratio did not. 4) In the maintenance and emergence stages, the 2 β /θ -ratio showed improved reliability. Implications: The ratio of powers in EEG frequency bands 2 β and  derived from the frontal cortex EEG channels has combined benefits of substantial sensitivity and noise resistance in measuring anesthesia depth.