Monitoring the depth of anesthesia: Methods based on EEG signal processing

Characterizing, measuring, and continuously monitoring the depth of anesthesia has been pursued extensively and persistently for many decades. Since the EEG signal originates from the synaptic activity and the CNS is the target of anesthetics effect, the anesthesia depth measurement methods based on EEG attracted much more interest and a variety of EEG parameters acting as anesthesia depth indicator have been developed and applied to clinical anesthesia. One of the development of modern anesthesia is the ability to monitor the anesthesia, then such cases as overdose or introperative awareness can be reduced to a lower chance.; In this paper, a variety of EEG parameters based on spectral analysis were overviewed and clinical application of these parameters were presented and compared. During propofol anesthesia, some parameters showed more advantages in monitoring the anesthesia depth than other parameters. Furthermore, the ratio of powers in the frequency bands of beta2 and theta waves in EEG signals (termed beta2/theta-ratio) is evaluated as a potential enhancement in measuring anesthesia depth, in comparison to the relative beta-ratio which is commercially used in the BIS monitor. Sensitivity and reliability of the beta2/theta-ratio, and EEG measurement locations are studied for their effectiveness in measuring anesthesia depth during different stages of anesthesia (awareness, induction, maintenance, and emergence). Data analysis is performed that indicates that the beta 2/theta-ratio and certain EEG electrode locations offer advantages of improved reliability in anesthesia depth measurements.