Discussion
thoracoabdominal aortic aneurysm, muscle twitch
In this randomized controlled trial, sugammadex reversal of NMB increased BIS in both shallow and deep anesthesia groups despite maintaining a steady state of propofol-remifentanil infusion and had a greater influence on the arousal in shallow than in deep anesthesia group. Previous studies only used the BIS as a measure of awakening after sugammadex administration, which might be disputed because BIS values are falsely increased by an activated EMG signalThe differential influence of sugammadex reversal of NMB with the anesthetic depth could be explained by “afferentation.” Unexpected movements and increased BIS could be considered an evidence of awakening induced by an increased afferent signal, as in previous studiesBinding between sugammadex and propofol may serve as an alternative pharmacokinetic mechanism that contributes to the differential effects of sugammadex based on the level of sedation. This possibility was previously dismissed because of the low affinity between the propofol and sugammadex molecules; nevertheless, it has recently regained attention. Computer modeling and ex vivo brain-slice data indicated the possibility of a decrease in free propofol concentration within the central compartment due to the binding between propofol and sugammadex in the presence of excess free sugammadex. This suggests that a potential modest reduction in the effects of propofol could not be completely ruled outThe clinical features that were considered signs of awakening in the current study are disputable in that the movements could be unmasked spinal withdrawal reflexes to noxious stimuli. A relatively shallow level of hypnosis could not suppress the reflex response to noxious stimuli caused by the endotracheal tube or surgical site painWe demonstrated that if the depth of hypnosis was relatively shallow, even within the range of general anesthesia, sugammadex reversal of NMB could trigger clinical signs of awakening. Under normal circumstances, in which sugammadex is administered for tracheal extubation at the end of surgery, this reversal is not problematic. However, if a clinical need for sudden reversal of NMB arises during surgery, these signs may have clinical implications. For example, intraoperative neuromonitoring may be required in thyroid, neuro, ear, or thoracoabdominal aortic aneurysm surgery, in which clinicians may use sugammadex to resume normal muscle twitch activityOur study had several limitations. First, this study was conducted at a single center; therefore, the generalizability of our findings is limited, and external validation is required. Furthermore, our explanations of the results of this study are based on the assumption that awakening due to increased afferent signals is the main cause of unexpected movements after sugammadex administration. However, based on our study design, we could not clarify the cause of the clinical signs of awakening after sugammadex administration. In addition, BIS values between 45 and 55 do not necessarily indicate an adequate depth of anesthesia