Abstract
On sedation motivated by the clinical needs for safety and reliability, recent studies have attempted to identify brain-specific signatures for tracking patient transition into and out of consciousness, but the differences in neurophysiological effects between 1) the sedative types and 2) the presence/absence of surgical stimulations still remain unclear. Here we used multimodal electroencephalography–functional near-infrared spectroscopy (EEG–fNIRS) measurements to observe electrical and hemodynamic responses during sedation simultaneously. Forty healthy volunteers were instructed to push the button to administer sedatives in response to auditory stimuli every 9–11 s. To generally illustrate brain activity at repetitive transition points at the loss of consciousness (LOC) and the recovery of consciousness (ROC), patient-controlled sedation was performed using two different sedatives (midazolam (MDZ) and propofol (PPF)) under two surgical conditions. Once consciousness was lost via sedatives, we observed gradually increasing EEG power at lower frequencies (<15 Hz) and decreasing power at higher frequencies (>15 Hz), as well as spatially increased EEG powers in the delta and lower alpha bands, and particularly also in the upper alpha rhythm, at the frontal and parieto-occipital areas over time. During ROC from unconsciousness, these spatio-temporal changes were reversed. Interestingly, the level of consciousness was switched on/off at significantly higher effect-site concentrations of sedatives in the brain according to the use of surgical stimuli, but the spatio-temporal EEG patterns were similar, regardless of the sedative used. We also observed sudden phase shifts in fronto-parietal connectivity at the LOC and the ROC as critical points. fNIRS measurement also revealed mild hemodynamic fluctuations. Compared with general anesthesia, our results provide insights into critical hallmarks of sedative-induced (un)consciousness, which have similar spatio-temporal EEG-fNIRS patterns regardless of the stage and the sedative used.
Highlights
Sedation is a rapidly growing technique in anesthesia care, and has become a great alternative to general anesthesia, which is considered to induce “deeper sedation” on a continuous spectrum
Despite the existence of approaches for measuring neurophysiological changes in the brain under general anesthesia [9,10,11,12,13,14,15], no studies have yet macroscopically investigated the neurophysiological dynamics of the transition points of consciousness at the level of sedation [9, 15, 16]
Previous studies mainly focused on the level of consciousness under the effect of general anesthesia
Summary
Sedation is a rapidly growing technique in anesthesia care, and has become a great alternative to general anesthesia, which is considered to induce “deeper sedation” on a continuous spectrum It is utilized for many surgical procedures such as dental procedure, plastic and reconstructive surgery, gastrointestinal endoscopy, etc [1, 2]. Clinical problem (e.g., oversedation) can be caused by large discrepancies in patient history, sedative preference, institutional bias, and patient/practitioner variability [5,6,7,8] In this respect, for safe sedation by general practitioner monitoring levels of consciousness is an important clinical issue during conscious sedation. These are crucial factors for the precise estimation of the brain state of patients under surgical condition
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