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

BACKGROUND: 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. METHODS: 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 >= 60%. Baseline variability, prediction probability, and agreement analysis between indices were evaluated. Clinical markers of loss of consciousness were also assessed. RESULTS: 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 mu g/mL. The BIS stabilized at values of 40-20 when the propofol concentrations at the effect site increased from 7 to 10 mu g/mL. The mean BIS-CSI difference was -7.4 with 95% limits of agreement of 22.2 and -36.9. The BlS 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). CONCLUSION: 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.