Time-variant non-linear phase-coupling analysis of EEG burst patterns in sedated patients during electroencephalic burst suppression period

Objectives: The quadratic phase-coupling (QPC) within burst patterns during electroencephalic burst suppression has been quantified. Methods: It can be shown that a QPC exists between the frequency ranges 0–2.5 and 3–7.5 Hz and between the frequency ranges 0–2.5 and 8–12 Hz. By means of time-variant bicoherence analysis, a strong phase-locking between the modulating and the modulated component can be identified. The phase-locking is demonstrable within the first 250 ms after the burst onset and comes up to the maximum between 750 and 1250 ms. Results: The effect is maintained over the whole first part of the burst (2 s) with a decreasing tendency after 1250 ms. All these effects cannot be found in the EEG before entering the burst suppression period (BSP). The transient coupling phenomena in the EEG bursts during BSP can be regarded as indicators for short-term interrelations between the underlying electrophysiologic processes. Conclusions: It can be suggested that the method introduced for the quantification of the sedation depth should be used.