Comment on “Effects of neuromuscular block on systemic and cerebral hemodynamics and bispectral index during moderate or deep sedation in critically ill patients” by Inoue et al.

Excerpt

Sir: We read with great concern the recent contribution by Inoue and coworkers [1] in Intensive Care Medicine because we think that their methodology and conclusions are rather misleading. The bispectral index (BIS) was been used to measure the level of sedation in critically ill patients. The greatest problems reported with this tool are the artifacts raising from facial muscle or eye movements and the wide variability in clinical conditions in ICUs [2]. BIS-XP is a newly available device (Aspect Medical, USA) with an additional frontal electrode, which should minimize movement-related artifacts. However, some authors suggest that the two methods are similar in measuring sedation in the ICU [3]. Inoue and coworkers present the “afferent muscle spindle theory” [4], suggesting that the lack of signals coming from muscle stretch receptors after neuromuscular blockade (NMB) reduces arousal center stimulation in cats. According to the authors, this theory contrasts to the more common idea that the lack of electromyographic (EMG) activity is the major cause of the decrease in the BIS score in paralyzed human beings. Inoue and coworkers believe that, “[R]emoval of EMG interference can affect the BIS to some degree. However, … the BIS is affected at least partially by altered consciousness status due to muscular relaxation.” We would like to know what physiological study has ever confirmed that NMB decreases the level of consciousness in human beings. We do not believe that the authors are in a position to maintain this based on the contents of their manuscript or an old study performed in cats. We should not confuse the elements of a good anesthesia, meaning sedation, pain relief, and muscle relaxation. The experience described by patients suffering awareness and posttraumatic distress syndrome events confirm the dramatic consequences of moderate/light sedation with NMB [5]. …