Comparative evaluation of the cerebral state index and the bispectral index during target-controlled infusion of propofol

Background. Cerebral state index (CSI) has recently been introducedas an intra-operative monitor of anaesthetic depth. We comparedthe performance of the CSI to the bispectral index (BIS) inmeasuring depth of anaesthesia during target-controlled infusion(TCI) of propofol. Methods. Twenty Chinese patients undergoing general anaesthesiawere recruited. CSI and BIS, and predicted effect-site concentrationof propofol were recorded. The level of sedation was testedby Modified Observer's Assessment of Alertness/Sedation Scale(MOAAS) every 20 s during stepwise increase (TCI, 0.5 µgml^–1) of propofol. The loss of verbal contact (LVC) andloss of response (LOR) were defined by MOAAS values of 2–3and less than 2, respectively. Baseline variability and theprediction probability (P_K) were calculated for the BIS andCSI. The values of BIS₀₅ and CSI₀₅, BIS₅₀ and CSI₅₀, BIS₉₅ andCSI₉₅ were calculated at each end-point (LVC and LOR). Results. Baseline variability of CSI was more than that of BIS.Both CSI and BIS showed a high prediction probability for thesteps awake vs LVC, awake vs LOR, and LVC vs LOR, and good correlationswith MOAAS values. Conclusion. Despite larger baseline variation, CSI performedas well as BIS in terms of P_K values and correlations with stepchanges in sedation.