Validation of the index of consciousness during sevoflurane and remifentanil anaesthesia: a comparison with the bispectral index and the cerebral state index

Background. The purpose of this study was to validate a new level of consciousness monitor derived from the EEG, called the index of consciousness (IoC), by comparing it with the bispectral index (BIS) and the cerebral state index (CSI) during general anaesthesia for cardiac surgery using sevoflurane, remifentanil, and atracurium. Methods. After ethical committee approval and written patient consent, data from 35 patients [31 males, four females, age 55 (10) yr] were recorded during general anaesthesia for elective cardiac bypass surgery. All patients were induced with sevoflurane 8%, until the Observer's Assessment of Alertness and Sedation (OAAS) scale level 1 was reached, and then was set at a 1% end-tidal sevoflurane concentration. Subsequently, remifentanil and atracurium were administered, the trachea was intubated, and the procedure continued as usual. To assess accuracy, the prediction probability (Pk) was calculated both during induction and during maintenance. Results. The Pk values [mean (SE)] for IoC, BIS, and CSI during induction were 0.90 (0.01), 0.90 (0.01), and 0.88 (0.01), respectively, whereas the corresponding Pk values during maintenance were 0.95 (0.01), 0.94 (0.01), and 0.60 (0.01). Conclusions. The three indices performed equally well during the induction phase and were able to predict the level of consciousness of the patients satisfactorily. During maintenance, the IoC and the BIS showed good agreement with the clinical signs. The CSI was significantly influenced by the administration of atracurium; therefore, the agreement with the OAAS scale during the maintenance phase was significantly less for CSI than for IoC and BIS.