Use of Processed Electroencephalography in the Clinical Setting

Abstract

Purpose of review: Processed electroencephalography (pEEG) is widely used in clinical practice. Few clinicians utilize the full potential of these devices. This brief review will address the improvements in patient management available from the utilization of all pEEG data.

Recent findings: Anesthesiologists easily learn to recognize raw pEEG patterns that are consistent with an appropriate level of hypnotic effect. Power distribution within the waveform can be displayed in a visual format that identifies signatures of the principal anesthetic hypnotics. Opinion on the benefit of pEEG data in the mitigation of postoperative neurological impairment remains divided.

Summary: Looking beyond the index number can aid clinical decision making and improve confidence in the benefits of this monitoring modality.

Keywords: Alpha/delta pattern; BIS; Bispectral index; Density spectral array; Excessive anesthesia; Postoperative neurological deterioration; Power spectra; Processed electroencephalography; pEEG.

Fig. 1

Progressive changes in the raw EEG with increasing concentration of GABA_A hypnotic agent. A–E show a decrease in frequency and increase in amplitude, followed by burst suppression and an isoelectric line. C shows the sedated state with alpha and beta oscillations but no delta component; episodes of explicit recall are likely. D and E show the onset of slow delta waves and are consistent with appropriate surgical hypnosis (‘wind waves riding on the background ocean swell’). (Reproduced with permission from [55])

Figure 2

a Appearance of delta waves in a raw pEEG trace. The waveform sweep speed has been slowed to 12.5 mm/s and then frozen to facilitate ready observation of this feature. The low-frequency filter must be turned off to see delta waves with the BIS device. To confirm these as delta oscillations, the number of peaks per second of frozen trace (or seconds of trace per peak) should be measured on the screen. b Appearance of alpha waves in a raw pEEG trace. The waveform sweep speed has been increased to 50 mm/s before freezing in this instance. To confirm these as alpha oscillations, the number of peaks per second of frozen trace should be measured

Fig. 3

Changes in the DSA spectrum of frontal EEG for sevoflurane (top) and propofol (bottom) with age. Relative power is color-coded as per the dB scale. The Y axis is frequency (Hz) and the X axis is age (years). A decrease in alpha power (8–12 Hz) generated by each of the agents is seen with increasing age. The agent ‘signatures’ are demonstrated also. Propofol has two bands of high power in the alpha and delta ranges, whereas sevoflurane shows the typical “fill-in” effect due to high power in the theta band (5–7 Hz). Reproduced with permission from reference [59])

Fig. 4

a Visual presentation of pEEG power distribution between five principle frequency bands and the accompanying simultaneous raw waveform for a subject receiving propofol/remifentanil TIVA. Notable power peaks are seen in the alpha and delta regions, consistent with appropriate hypnosis from this mode of anesthesia. Scale of the X and Y axes for the raw waveform are respectively 1 s and 50 μV per graticule. b Visual presentation of pEEG power as a density spectral array and the accompanying simultaneous raw waveform (marked by the vertical white line) for a subject receiving propofol/remifentanil TIVA. High-power tracts are seen in the alpha and delta regions, consistent with appropriate hypnosis from this mode of anesthesia. Power is color-coded as per the displayed scale, and the X axis represents the time of day. Scales of the X and Y axes for the raw waveform are respectively 1 s and 30 μV per graticule