The effects of electromyographic activity on the accuracy of the Narcotrend monitor compared with the Bispectral Index during combined anaesthesia

Abstract

The Narcotrend is a monitor system for the assessment of depth of anaesthesia. The objective of this trial was to investigate the susceptibility of the Narcotrend to electromyographic (EMG) activity when compared with the Bispectral Index (BIS). We enrolled 33 patients undergoing major urological procedures under combined anaesthesia (thoracic epidural analgesia and general anaesthesia). Anaesthetic depth was assessed simultaneously by the BIS XP and Narcotrend. The intended anaesthetic depth ranged between 40 and 55 in the BIS and between D2 and D0 in the Narcotrend. BIS, but not Narcotrend, values correlated significantly (p < 0.0001) with EMG. BIS values between 70 and 80 occurred intermittently above an EMG activity of 35 dB, whereas the Narcotrend and the clinical signs remained unchanged during the period of elevated BIS values. None of the patients reported intra-operative awareness. Increased electromyographic activity does not affect Narcotrend values. Under combined anaesthesia, the Narcotrend monitor is more reliable when compared with the BIS regarding susceptibility to increased EMG activity.