Comparative study of Poincare plot analysis using short electroencephalogram signals during anaesthesia with spectral edge frequency 95 and bispectral index

The return or Poincare plot is a non-linear analytical approach in a two-dimensional plane, where a timed signal is plotted against itself after a time delay. Its scatter pattern reflects the randomness and variability in the signals. Quantification of a Poincare plot of the electroencephalogram has potential to determine anaesthesia depth. We quantified the degree of dispersion (i.e. standard deviation, SD) along the diagonal line of the electroencephalogram-Poincare plot (named as SD1/SD2), and compared SD1/SD2 values with spectral edge frequency 95 (SEF95) and bispectral index values. The regression analysis showed a tight linear regression equation with a coefficient of determination (R-2) value of 0.904 (p<0.0001) between the Poincare index (SD1/SD2) and SEF95, and a moderate linear regression equation between SD1/SD2 and bispectral index (R-2=0.346, p<0.0001). Quantification of the Poincare plot tightly correlates with SEF95, reflecting anaesthesia-dependent changes in electroencephalogram oscillation.