The fundamental contribution of the electromyogram to a high bispectral index: a postoperative observational study


The electromyogram (EMG) activity has been reported to falsely increase BIS. Conversely, EMG seems necessary to constitute the high BIS indicative of an awake condition, and may play a fundamental role in calculating BIS, rather than distorting the appropriate BIS. However, exactly how EMG is associated with a high BIS remains unclear. We intended to clarify the respective contributions of EMG and various electroencephalogram (EEG) parameters to high BIS. In 79 courses of anaesthesia, BIS monitor-derived EMG parameters (EMGLOW), and other processed EEG parameters [SEF95 (spectral edge frequency 95%), SynchFastSlow (bispectral parameter), BetaRatio (frequency parameter), total power subtypes in five frequency range], were obtained simultaneously with BIS, every 3 s. These EEG parameters were used for receiver operating characteristic (ROC) analysis of detecting three BIS levels (BIS > 80, BIS > 70, and BIS > 60) to assess their diagnosabilities. A total of 218,418 data points derived from 79 cases were used for analysis. Area under the ROC curve (AUC) was calculated and optimal cut-off (threshold) was determined by Youden index. As the results, for detecting BIS > 80, the AUC of EMGLOW was 0.975 [0.974–0.977] (mean [95% confidence interval]), significantly higher than any other processed EEG parameters such as BetaRatio (0.832 [0.828–0.835]), SEF95 (0.821 [0.817–0.826]) and SynchFastSlow (0.769 [0.764–0.774]) (p < 0.05 each). The threshold of EMGLOW for detecting BIS > 80 was 35.7 dB, with high sensitivity (92.5%) and high specificity (96.5%). Our results suggest EMG contributes considerably to the diagnosis of high BIS, and is particularly essential for determining BIS > 80.

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This work was partly supported by a Grant-in-Aid for Scientific Research (C) from the Japan Society for the Promotion of Science (JSPS KAKENHI No. 15K10518), Tokyo, Japan.

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Correspondence to Kazuko Hayashi.

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EEG analyzer f-PIS monitor

The EEG analyzer f-PIS monitor (Fourier-analysis-coordinated Poincare-plot Integrated Score monitor) is an electroencephalogram analyzer for anaesthesia depth, developed by one of our co-authors (T. Sawa). Briefly, using the JAVA Apache Commons Math library for arithmetic functions and the JAVA Swing library for GUI, he developed an online system that enables transmission and various analyses of EEG packets from the BIS monitor. In the system, frequency analysis with multiple FIR-filters is available, as well as bispectral analysis and power spectral analysis from captured EEG. “Processing 3” supported by JAVA was used to develop this system. He compiled the program codes with a JAVA virtual machine and created a standalone application software named “EEG analyzer f-PIS monitor” (Version 45_SR, 46_SR) [36].

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Hayashi, K., Sawa, T. The fundamental contribution of the electromyogram to a high bispectral index: a postoperative observational study. J Clin Monit Comput 33, 1097–1103 (2019).

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  • Bispectral index
  • Electromyogram
  • Awareness
  • Anaesthesia depth
  • Monitoring