Quantitative EEG changes associated with loss and return of consciousness in healthy adult volunteers anaesthetized with propofol or sevoflurane

Abstract

Significant changes in topographic quantitative EEG (QEEG) features were documented during induction and emergence from anaesthesia induced by the systematic administration of sevoflurane and propofol in combination with remifentanil. The goal was to identify those changes that were sensitive to alterations in the state of consciousness but independent of anaesthetic protocol. Healthy paid volunteers were anaesthetized and reawakened using propofol/remifentanil and sevoflurane/remifentanil, administered in graded steps while the level of arousal was measured. Alterations in the level of arousal were accompanied by significant QEEG changes, many of which were consistent across anaesthetic protocols. Light sedation was accompanied by decreased posterior alpha and increased frontal/central beta power. Frontal power predominance increased with deeper sedation, involving alpha and, to a lesser extent, delta and theta power. With loss of consciousness, delta and theta power increased further in anterior regions and also spread to posterior regions. These changes reversed with return to consciousness.

Electroencephalogram signatures of loss and recovery of consciousness from propofol

“…We postulate, based on our modeling studies, that spatially coherent alpha oscillations contribute to propofol-induced unconsciousness by drastically restricting communication within frontal thalamo-cortical circuits to this narrow frequency band (39). Several studies have shown that low-frequency oscillations are more prominent with increasing anesthetic dose and levels of unconsciousness (6,8,21,22,25). In recent multiscale human intracranial studies of propofol-induced unconsciousness, Lewis et al (46) found that neuronal spiking is limited to a brief phase window of the slow oscillation, and is silent otherwise.…”

“…A variety of EEG patterns are known to arise during GA maintained by both GABA A receptor-specific and ether-derived anesthetics. These EEG patterns include increases in frontal EEG power (20)(21)(22)(23)(24), a shift in EEG power toward lower frequencies (25), changes in coherence (22,26), and burst suppression and isoelectricity (27). However, the relationship between these or other EEG patterns…”

Sleep and general anesthesia

“…Most general anesthetics (the main exceptions being nitrous oxide and ketamine) produce both spindles (brief 7-14 Hz bursts of activity) and delta waves (1-4 Hz), with the spindles generally occurring first, followed by sustained large amplitude delta oscillations at or beyond the point at which consciousness is lost. [48][49][50][51][52] As mentioned above, these same two features, spindles and delta oscillations, are the characteristic hallmarks of falling asleep and deep sleep. Figure 3 shows Power Spectra that illustrate the similarities between the EEG during non-REM sleep and dexmedetomidineinduced LORR.…”

Monitoring sedation in the critically ill child

“…Table 5 Domains evaluated in the clinical scales frequently used in children. .......................................................................................................................................... [24]. There are several systems that analyse cortical activity and process the EEG signal in order to evaluate the level of sedation; the most widely used are the BIS (Aspect Medical Systems, Newton, MA, USA), MLAEPs (ALARIS Medical Systems, Danmeter A ⁄ S, Odense, Denmark), patient state index (PSI; Physiometrix, North Billerica, MA, USA), cerebral state monitor (CSM; Danmeter A ⁄ S, Odense, Denmark), Narcotrend (MonitorTechnik, Bad Bramstedt, Germany), and response entropy and state entropy (Datex-Ohmeda Division, Instrumentarium Corporation, Helsinki, Finland).…”