J Dent Anesth Pain Med.  2017 Dec;17(4):241-251. 10.17245/jdapm.2017.17.4.241.

Characteristics of electroencephalogram signatures in sedated patients induced by various anesthetic agents

• Choi BM

• KMID: 2399794
• DOI: http://doi.org/10.17245/jdapm.2017.17.4.241

Abstract

Devices that monitor the depth of hypnosis based on the electroencephalogram (EEG) have long been commercialized, and clinicians use these to titrate the dosage of hypnotic agents. However, these have not yet been accepted as standard monitoring devices for anesthesiology. The primary reason is that the use of these monitoring devices does not completely prevent awareness during surgery, and the development of these devices has not taken into account the neurophysiological mechanisms of hypnotic agents, thus making it possible to show different levels of unconsciousness in the same brain status. An alternative is to monitor EEGs that are not signal processed with numerical values presented by these monitoring devices. Several studies have reported that power spectral analysis alone can distinguish the effects of different hypnotic agents on consciousness changes. This paper introduces the basic concept of power spectral analysis and introduces the EEG characteristics of various hypnotic agents that are used in sedation.

Keyword

Depth of Hypnosis; Electroencephalogram; Hypnotics; Power Spectral Analysis; Sedation

MeSH Terms

Anesthesiology
Anesthetics*
Brain
Consciousness
Electroencephalography*
Humans
Hypnosis
Hypnotics and Sedatives
Unconsciousness
Anesthetics
Hypnotics and Sedatives

Figure

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  Fig. 1 Sinusoids with amplitude 1, frequency 1, phase angle 0° and 90° (π/2 rad): f(t) = sin(2π · t): solid blue line and sin(2π · t + π/2): dotted green line.

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  Fig. 2 A vector with a size of A2 and phase angle of θ.

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  Fig. 3 Sinusoids with various frequencies, amplitudes, and phase angles. The four sinusoids are elements with frequency 1, 2, 3, 5 Hz, respectively, and their amplitudes are 1, 0.8, 1.5, and 0.5, respectively. The phase angles are 90°, 270°, 315° and 90°.

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  Fig. 4 Addition of four sinusoids in Fig. 3:xk=1·sin2π·1·k·Δt+0.5π+1.5·sin2π·2·k·Δt+1.5π+1·sin2π·3·k·Δt+1.7π+2·sin2π·4·k·Δt+1.5·sin2π·5·k·Δt+0.5π

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  Fig. 5 Analysis process from the raw electroencephalogram (EEG) to the spectrogram. A: raw EEG, B: filtered with two major oscillations, C: power spectral analysis, D: three-dimensional spectrogram change over 30 min, E: Spectrogram change over time presented in two-dimensional space (density spectral array).

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  Fig. 6 Representative spectrogram from a single subject during sedation with propofol. Progressive decrease in peak frequency and progressive increase in αβ power are shown. Corresponding MOAA/S is illustrated as black step lines. This figure is adapted, with permission, from LeeHS. et al: Diversity of functional connectivity patterns is reduced in propofol-induced unconsciousness. Human Brain Mapping 2017; 38: 4980–4995.

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  Fig. 7 Raw electroencephalogram segment. A spindle (red box) showing oscillation at 9–15 Hz is observed, a characteristic EEG finding when sedation is induced by dexmedetomidine.

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