Comparison of two depth of anaesthesia monitors during general anaesthesia: Electrophysiological and clinical assessment

Abstract

Cerebral state monitor (CSM) is a recently developed anaesthesia depth monitor based on EEG measurement. Medline search confirmed that the accuracy of this monitor has already been compared with BIS monitoring; however, we did not find any studies comparing CSM monitor with AEP monitoring. Therefore, the aim of our study was to investigate the correlation between AAI using AEP monitor and CSI (cerebral state index) using CSM monitor. Prospective, observational study involving 39 ASA I-III patients undergoing lumbar discuss hernia operation. Simultaneous registration of CSI and AAI was performed during general anaesthesia. The identical values were off-line analysed. Additionally in 20 patients parallel registration of CSI and AAI was undertaken while anaesthesia was guided based on routine clinical signs. While analysing the data in the superficial, ideal and deep anaesthesia zones, we found that a relationship between CSI and AAI is weak. Our patients spent roughly the half of the clinical anaesthesia in the ideal zone based on the AAI index and less than 50% based on CSI. Almost one fifth of clinical anaesthesia based on AAI and nearly 40% based on CSI was spent in the deep anaesthesia zones. A superficial anaesthesia has been detected in 27% of time based on AAI and 17% based on CSI. CSI and AAI weakly correlated to each other. Depth of anaesthesia monitors may be useful in detecting patients who spend valuable time within the deep anaesthetic zone.