Comparison of the effect of electromyogram activity during emergence on anesthetic depth monitoring between phase lag entropy and bispectral index: a prospective observational study

BACKGROUND The bispectral index (BIS) is the most widely used algorithm for measuring anesthetic depth. The BIS has been demonstrated as inaccurate when neuromuscular blocking drugs (NMBDs) are used. Compared with BIS, phase lag entropy (PLE), which measures the anesthetic depth based on a 4-channel EEG signal, is less affected by EMG. The purpose of this study was to compare the effect of EMG activity during emergence on anesthetic depth monitoring between PLE and BIS. METHODS Twenty five consecutive patients with physical status I-II of American Society of Anesthesiologists undergoing general anesthesia (age range, 20-60 years). The anesthesiologist attached the sensors of BIS and PLEM 100 on the patient's forehead. NMB reversal was performed by intravenously injecting sugammadex after confirmation of shallow NMB (TOF count 1-4) under neuromuscular monitoring. The BIS and PLE scores were recorded with neuromuscular monitoring at 1-min intervals for 5 min after administration of sugammadex. RESULTS The BIS and BIS-EMG measured at 1 min after sugammadex injection were significantly higher at 1 min [51.650 (46.100, 62.225) (P<0.001); 28.500 (27.800, 31.075) (P=0.003)] than at 0 min. However, there was no between-time point difference in the PLE score and PLE-EMG (P=0.0843, P=0.329). CONCLUSIONS In general anesthesia using propofol-remifentanil, the BIS at 1 min after sugammadex reversal during emergence appears to be more affected by EMG activity than the PLE score. Therefore, immediately after sugammadex administration (within 1 min), it may be clinically useful to evaluate the consciousness status through the PLE score.