Abstract
The Entropy™ module and bispectral index (BIS) depth-of-anesthesia monitors have been shown to be influenced by electromyographic (EMG) activity. The increase in entropy and BIS values is most likely caused by increased EMG activity and a higher level of consciousness. A strong EMG activity can increase entropy and BIS values because it is impossible to separate electroencephalography (EEG) from EMG, and this results from their overlapping power spectra. Thus, the entropy module may be more affected by EMG compared with the BIS module because it has more overlap with the power spectra of EEG and EMG. Several studies have suggested that EMG activity is most likely to increase, especially as it relates to the level of total intravenous anesthesia without a muscle relaxant or an insufficient analgesic level, which results in falsely increased entropy values. We present the case of a patient whose entropy values were falsely elevated by increased EMG activity resulting from light neuromuscular block or nociceptive stimuli during surgery even when undergoing desflurane anesthesia. This was closely related to the change in the neuromuscular block level and it was influenced by the degree of analgesia and the remifentanil infusion rate.