Intraoperative monitoring of depth of anesthesia by automated EMG-analysis

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The observation of a correlation between EEG-activity and concentrations of anaesthetic and analgetic agents led to the development of processed EEG-monoparameters. Amount these, the BIS (bispectral index) has come to widespread use. However, there is ongoing controversy regarding this method. While a significant reduction of intraoperative awareness has been demonstrated in the B-aware-trial, these results were not reproducible in the B-unaware-trial. Our group has investigated automated analysis of processed intraoperative cranial nerve EMG data for more than 10 years. During surgical procedures in which these techniques were developed and tested, spontaneous episodes of massive EMG-activity, mainly in the muscles of throat, tongue and pharynx, have been observed. Minutes after the beginning of these episodes, considerable patient movement would occur on several occasions. Thus, it was hypothesized that the activation of these muscles indicates the initiation of protective reflexes, and that the resulting EMG-activity might serve as a warning parameter. A pilot study was conducted, and EMG from the muscles of throat, tongue and pharynx was quantified. In a parallel fashion, the BIS was assessed. With these data, the time interval between extubation and clear rise of the monitoring parameters (BIS and EMG) was compared. A median time interval of 5.9min was found for the BIS, while the EMG-parameter would rise 12.3min before extubation in median. As a result, a significantly longer warning-intervall was calculated for the EMG-parameter with the Mann-Whitney-test (p = 0.026). Observations made during this study and contemporary literature suggest that these findings should in principle be transferable to facial nerve EMG, which may be assessed in a much more simple way in routine practice. The goal of the planned project is the development and evaluation of a fully automated quantitative system, which relies on facial nerve EMG as a warning parameter indicating arousal reactions and pending patient movement. In order to evaluate this system, the resulting warning parameter is to be correlated with the BIS and the following additional parameters: a.) PRST-score b.) Depth of analgesia (ANI-monitor) c.) Pharmacological depth of analgesia: Calculated effect compartment concentration for utilized opiate d.) Pharmacological depth of hypnosis: Calculated effect compartment concentration for Propofol. In succession of this project, these results may be used for a prospective evaluation of variations in the EMG-parameter with constant surgical stimulus under varying effect compartment concentrations of opiates.