LAUSR

Interference of electrical equipment and monitors is well recognised [1]. However, I would like to bring to your attention an interaction between our most recently added monitors that generated false readings, which may in turn lead to patient harm. Both processed electroencephalograph (pEEG) and neuromuscular blockade monitoring have been extremely topical in recent years, with both highlighted in the 2021Association guideline [2]. The interaction described has been seen repeatedly and I demonstrate a recent example. Having positioned and started a laparoscopic case, I had no easy access to place the quantitative ToFscan (Idmed, Marseille, France) on the patient’s hand. As is common practice, electrodes were placed on the patient’s face to monitor facial nerve stimulation qualitatively, as a second choice. After connecting, but not yet starting nerve stimulation, it was noted that there were several changes to displayed parameters on the bispectral index (BIS) monitor (Aspect Medical Systems Inc., Norwood, MA, USA). In particular, the BIS displayed increased from 45 (Fig. 1a) up to 63 (Fig. 1b). In addition, electromyography increased dramatically, causing the signal quality index to decrease significantly. The ToFscan product information does describe possible electrical interference [3]. However, it states “perturbations are transitional”, rather than constant, as was my experience. Although it is unclear why there would be electrical current between electrodes while inactive, there is a reasonably straightforward explanation. Assuming a small amount of electrical activity, the nearby BIS montage perceives the current in superficial muscles as muscle activity, which seems to alter the proprietary algorithm to consider the patient closer to waking, as reflected by a higher BIS [4]. Electrical interference is well recognised, with even ECG activity (inmillivolts) suggested to cause disturbance of the pEEG [5]. Since pEEGmeasures in microvolts, it will take only tiny electrical current or leakage to replicate these changes. The findings were easily repeatable, by disconnecting and reconnecting the electrodes. However, I have not been able to repeat this with two older qualitative neuromuscular blockade monitors, so this problem is more