Poincaré analysis of the electroencephalogram during sevoflurane anesthesia.

OBJECTIVE

The Poincaré plot is a two-dimensional state-space approach, where a timed signal is plotted against itself after a time delay, enabling determination of the dynamic nature of signals. Quantification of the Poincaré plot is a candidate for estimating anesthesia-dependent changes in the electroencephalogram (EEG).

METHODS

In 20 patients, at four different states of anesthesia (0.5%, 1%, 2% and 3% sevoflurane), frontal EEG signals (10s) were used to construct Poincaré plots. The plot pattern was quantified by the standard deviation of the voltage dispersion along the line of identity (SD2), the standard deviation perpendicular to the line of identity (SD1) and their ratio (SD1/SD2), and compared using spectral EEG features.

RESULTS

A significant stepwise decrease in the SD1/SD2 ratio was observed with each stepwise increase in sevoflurane concentration (p<0.001 for each). From 0.5% to 3% sevoflurane anesthesia, the ratio of relative β power to δ power (β/δ) was highly correlated with SD1/SD2 (R=0.92).

CONCLUSIONS

The Poincaré plot of the frontal EEG can detect the significant changes in the depth of anesthesia induced by different sevoflurane concentrations.

SIGNIFICANCE

The Poincaré plot is a useful technique for detecting the EEG changes induced by anesthesia.