Cerebral state index vs. bispectral index during sevoflurane-nitrous oxide anaesthesia

The cerebral state index (CSI) is a low-cost and compact electroencephalographic monitor alternative to the bispectral index (BIS). Although both indices are shown as the number between 0 and 100, owing to the different calculation algorithms, both indices might be different during anaesthesia. The present study was performed to compare the BIS and CSI during sevoflurane-nitrous oxide anaesthesia.

Forty patients scheduled for abdominal surgery aged 30-70 years were enrolled. The electrodes of both the cerebral state monitor and BIS were attached simultaneously. Anaesthesia was induced with midazolam and fentanyl, and was maintained with sevoflurane with 50% nitrous oxide in oxygen and intermittent epidural mepivacaine. During surgery, end-tidal sevoflurane concentration was kept at 0.5, 1.0, and 1.5% for more than 10 min to measure CSI and BIS.

The duration of signal disturbance by electric cautery was 12.6 +/- 4.2 min in the BIS and 3.9 +/- 1.8 min in the cerebral state monitor (P < 0.05) for 9.5 +/- 4.3 min duration of electric cautery. The recovery time from disturbance by electric cautery was 37 +/- 12 s in the BIS and 4 +/- 2 s in the cerebral state monitor (P < 0.05). The absolute values of the BIS and CSI were not significantly different. Both BIS and CSI decreased significantly when end-tidal sevoflurane concentration increased from 0.5 to 1.0%, but did not significantly change when end-tidal sevoflurane concentration increased from 1.0 to 1.5%. The BIS and CSI correlated well. The Bland-Altman plot showed good agreement between the BIS and CSI.

During sevoflurane-nitrous oxide anaesthesia, the CSI was not significantly different from the BIS in the awake state and with sevoflurane concentration 0.5-1.5%.