Performance of the cerebral state index during increasing levels of propofol anesthesia: a comparison with the bispectral index.

Abstract

The cerebral state monitor is a new device to measure depth of anesthesia. In this study we compared the cerebral state monitor with the bispectral index (BIS) monitor during propofol anesthesia. Fifteen healthy patients received a continuous infusion of propofol (300 mL/h). The cerebral state index (CSI) and the BIS values were recorded until burst suppression ratio > or =60%. Baseline variability, prediction probability, and agreement analysis between indices were evaluated. Clinical markers of loss of consciousness were also assessed. Mean awake BIS and CSI values were 95.6 and 91.6, respectively (P = 0.01). BIS and CSI prediction probability values (mean +/- sd) were estimated to be 0.87 +/- 0.08 and 0.86 +/- 0.08, respectively (NS). The CSI tended to stabilize at values of 60-40 when estimated propofol concentrations at the effect site increased from 5 to 8 mug/mL. The BIS stabilized at values of 40-20 when the propofol concentrations at the effect site increased from 7 to 10 mug/mL. The mean BIS-CSI difference was -7.4 with 95% limits of agreement of 22.2 and -36.9. The BIS and CSI correlation with the burst suppression ratio was -0.60 and -0.97, respectively (P < 0.01). Predicted BIS and CSI values for loss of eyelash reflex in 50% and 95% of the patients were different (P < 0.05). The overall performance of both monitors during propofol induction was similar. However, the different dynamic profiles of these monitors indicate that BIS may be a more useful index for evaluating intermediate anesthetic levels, whereas CSI may be better for evaluating deeper anesthetic levels.