Monitoring Anesthetic Brain States - The Spectral Analysis of the EEG
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).
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.
- Red = high power, blue = low power.
- 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.