Electroencephalographic dynamics of etomidate-induced loss of consciousness

Abstract

Background: Highly structured electroencephalography (EEG) oscillations can occur in adults during etomidate-induced general anesthesia, but the link between these two phenomena is poorly understood. Therefore, in the present study, we investigated the electroencephalogram dynamics of etomidate-induced loss of consciousness (LOC) in order to understand the neurological mechanism of etomidate-induced LOC.

Methods: This study is a prospective observational study. Etomidate-induced anesthesia was performed on eligible patients undergoing elective surgery. We analyzed EEG data from 20 patients who received etomidate for the induction of general anesthesia. We used power spectra and coherence methods to process and analyze the EEG data. Our study was based on 4-channel EEG recordings.

Results: Compared with the baseline (awake period), etomidate induced an increase in power in delta, theta, alpha and beta waves during LOC. Compared with the awake period, the delta-wave (1-4 Hz), alpha-wave(8-13 Hz), and theta-wave(4-8 Hz) coherence increased significantly during LOC, while the slow-wave (< 1 Hz) coherence decreased. However, the delta wave (1.0-4.0 Hz) during etomidate-induced LOC was more coherent than during the awake period (1.86-3.17 Hz, two-group test for coherence, p < 0.001).

Conclusions: The neural circuit mechanism of etomidate-induced LOC is closely related to the induction of oscillation in delta, theta, alpha and beta waves and the enhancement of delta-wave coherence.

Trial registration: ChiCTR1800017110.

Keywords: EEG; Etomidate; General anesthesia; LOC.

Fig. 1

The channel position and the two bipolar frontal channels: F7 and F8, which we used for coherence analysis

Fig. 2

Time-frequency analysis of EEG data between the awake period and etomidate-induced LOC. a During the awake period before induction of etomidate (n = 20), slow-wave (< 1.0 Hz) and delta-wave (1.0–4.0 Hz) oscillations were mainly present. b Etomidate-induced LOC (n = 20) yielded an increase in the power of slow waves (< 1.0 Hz), delta waves (1.0–4.0 Hz), theta waves (4.0–8.0 Hz), and alpha waves (8.0–13.0 Hz). c Spectrograms of the awake period. Compared with those during the awake period, the powers of the slow wave (< 1.0 Hz), delta wave (1.0–4.0 Hz), theta wave (4.0–8.0 Hz), and alpha wave (8.0–13.0 Hz) during the etomidate-induced LOC were significantly increased (C: 0–22.97 Hz, 27.28–40.00 Hz; p < 0.001, two-group test for spectra). Median spectra presented with 95 % jackknife CIs. Horizontal solid black lines represent the frequency ranges at which there were significant differences

Fig. 3

Frontal-lobe EEG spectrograms in the study of etomidate-induced LOC. a In the etomidate study, the main events are marked on the timeline. b During the study, each patient was instructed to keep their eyes closed and without motion for a period of 3 min before etomidate was administered to induce general anesthesia. The frequency is plotted on the y-axis and time is plotted on the x-axis. The energy or power in the signal is represented by color. As the induction of etomidate began, the slow-wave, delta-wave, and theta-wave oscillations increased. After LOC, the alpha wave oscillation increased

Fig. 4

Case selection. Our study initially included 40 individuals between 18 and 65 years old. We excluded 12 patients because of restlessness or other non-cooperative behaviors before anesthesia. We then examined the EEG data of the remaining 28 patients and excluded 8 patients due to poor data quality (Poor electrode contact and other reasons). Ultimately, we analyzed the EEG data from 20 patients

Fig. 5

Coherence analysis between the awake period and the period during etomidate-induced LOC. a The coherence analysis of the awake period (n = 20) showed the coherence spectrum in terms of the slow wave (< 1.0 Hz), delta wave (1.0–4.0 Hz), and alpha wave (8.0–13.0 Hz). b The coherence analysis during etomidate-induced LOC (n = 20) shows the coherence spectra in terms of the delta wave (1.0–4.0 Hz), theta wave (4.0–8.0 Hz), and the alpha wave (8.0–13.0 Hz). During the awake period, the coherence of slow waves (< 1.0 Hz) was decreased. c The coherence spectra of the awake period and the period during induced LOC. The alpha wave (8.0–13.0 Hz) coherence is similar in both periods. However, the delta wave (1.0–4.0 Hz) during etomidate-induced LOC was more coherent than during the awake period (1.86–3.17 Hz, two-group test for coherence, p < 0.001). Median coherence is presented with 95 % jackknife CIs. Horizontal solid black lines represent frequency ranges at which there was significant difference. The bandpass filter allows frequency components to pass within a certain frequency range but attenuates the frequency components in other ranges to a very low level rather than cutting off frequencies outside the range at a certain frequency point; therefore, at 40 Hz, the graph shows that the coherence is uniform and rising