The Spectral Analysis of the EEG

A segment of EEG can be decomposed into a plot of its power (usually in dB) as a function of frequency. This plot is termed the power spectrum. Because the spectrum captures only one instance in time it has limited utility during a dynamic anesthetic state (Fig. 11.3).

3D spectrogram

Taking the spectrum plots at several adjacent time intervals and stacking them together forms a 3D spectrogram. The spectrogram is a plot of power by frequency as a function of time.

1. Red = high power, blue = low power.
2. The 3D spectrogram can be flattened into to a 2D plot which is displayed on monitors in the operating room (Fig. 11.4). The 2D spectrogram plot is also termed the density spectral array. The 3D spectrogram is also termed the compressed spectral array.

Figures

Outline

• General Considerations
• Electroencephalogram-Based Indices of Level of Consciousness
• End-Tidal Anesthetic Criterion
• The Spectral Analysis of the EEG
• Effects of Different Anesthetics on the Brain
• Conclusion
• Suggested Readings