A Pilot Investigation Evaluating Relative Changes in Fronto-Occipital Alpha and Beta Spectral Power as Measurement of Anesthesia Hypnotic Depth

Abstract

BACKGROUND: Other than clinical observation of a patient’s vegetative response to nociception, monitoring the hypnotic component of general anesthesia (GA) and unconsciousness relies on electroencephalography (EEG)-based indices. These indices exclusively based on frontal EEG activity neglect an important observation. One of the main hallmarks of transitions from wakefulness to GA is a shift in alpha oscillations (7.5–12.5 Hz activity) from occipital brain regions toward anterior brain regions (“alpha anteriorization”). Monitoring the degree of this alpha anteriorization may help to guide induction and maintenance of hypnotic depth and prevent intraoperative awareness. However, the occipital region of the brain is completely disregarded and occipital alpha as characteristic of wakefulness and its posterior-to-anterior shift during induction are missed. Here, we propose an application of Narcotrend’s reduced power alpha beta (RPAB) index, originally developed to monitor differences in hemispheric perfusion, for determining the ratio of alpha and beta activity in the anterior-posterior axis. METHODS: Perioperative EEG data of 32 patients undergoing GA in the ophthalmic surgery department of Bern University Hospital were retrospectively analyzed. EEG was recorded with the Narcotrend® monitor using a frontal (Fp1-Fp2) and a posterior (T9-Oz) bipolar derivation with reference electrode over A2. The RPAB index was computed between both bipolar signals, defining the fronto-occipital RPAB (FO-RPAB). FO-RPAB was analyzed during wakefulness, GA maintenance, and emergence, as well as before and after the intraoperative administration of a ketamine bolus. FO-RPAB was compared with a classical quantitative EEG measure—the spectral edge frequency 95% (SEF-95). RESULTS: A significant shift of the FO-RPAB was observed during both induction of and emergence from GA (P < .001). Interestingly, the additional administration of ketamine during GA did not lead to a significant change in FO-RPAB (P = 0.81). In contrast, a significant increase in the SEF-95 in the frontal channel was observed during the 10-minute period after ketamine administration (P < .001). CONCLUSIONS: FO-RPAB appears to qualify as a marker of unconsciousness, reflecting physiological fronto-occipital activity differences during GA. In contrast to frontal SEF-95, it is not disturbed by additional administration of ketamine for analgesia.

Alpha anteriorization and theta posteriorization during deep sleep

“…Recent studies have made efforts on examining the spatial distribution of physiological activities in the wake state (Frauscher et al., 2018), spatial characteristics of spindles (Piantoni et al., 2017), and functional connectivity during sleep and anesthesia (Banks et al., 2020). A recent study has shown that the fronto‐occipital alpha and beta spectral power contributes to the measurement of anesthesia hypnotic depth (Fehrlin et al., 2023). The above findings inspire the use of EEG power anteriorization/posteriorization as an additional dimension for automated sleep scoring.…”

“…Among others, alpha anteriorization, a phenomenon characterized by the EEG alpha‐power shift from the occipital lobe to the frontal lobe, was found to be an EEG signature of loss of consciousness from propofol (Purdon et al., 2013) and sevoflurane (Blain‐Moraes et al., 2015). This phenomenon has attracted widespread attention in anesthesia (Fehrlin et al., 2023), but not in sleep research.…”

“…found to be an EEG signature of loss of consciousness from propofol (Purdon et al, 2013) and sevoflurane (Blain-Moraes et al, 2015). This phenomenon has attracted widespread attention in anesthesia (Fehrlin et al, 2023), but not in sleep research.…”

Effect of Continuous Infusion of Different Doses of Esketamine on the Bispectral Index During Sevoflurane Anesthesia: A Randomized Controlled Trial

“…This requires us to look for new markers of unconsciousness that are not disturbed by esketamine administration in the future. 51 …”

Processed EEG for personalized dosing of anesthetics during general anesthesia

“…Unter Allgemeinanästhesie kommt es zu einer typischen Abnahme der Konnektivität zwischen Hirnregionen [ 111 – 113 ]. Neben der rein frontalen EEG-Ableitung für die Generierung der derzeitigen „Anästhesietiefe“ könnten wohl zusätzlich okzipitale Kortexregionen für die Beurteilung von Veränderungen des Bewusstseins genutzt werden [ 114 , 115 ]. Die Messung solcher dynamischen neurobiologischen Prozesse wie der Alpha-Anteriorisierung unter Narkose findet aber v. a. aus Gründen der Praktikabilität noch keine breite klinische Anwendung [ 115 – 117 ].…”