Evaluation of bispectral index (BIS) for anaesthetic depth monitoring in pigs

Introduction: Bispectral index (BIS) is a promising method for monitoring a naesthetic depth in humans. Inhalational and intravenous anaesthetics produ ce dose-dependent effects on electroencephalogram-derived parameters, such as bispectral index (BIS). Significant correlations between decrease of BIS values in humans and end-tidal concentrations of volatile anaesthetics hal othane, isoflurane, desflurane and sevoflurane and plasma propofol concentr ations have been reported in several investigations. We have investigated t he effect of xenon anaesthesia on bispectral index (BIS) in pigs. Materials and Methods: BIS index was measured under total intravenous, xeno n and halothane anaesthesia: in 8 pigs. Each animal received 1 MAC halothan e before or after xenon anaesthesia in randomized cross over design to elim inate systemic errors. Between xenon and halothane anaesthesia total intrav enous anaesthesia was applied to eliminate the effects of the anaesthetic g as first applied. Surgical stimuli were not present during xenon and haloth ane anaesthesia, surgical preparations were completed in TIVA. BIS levels m easured during preparation phase were used as reference values to assure ad equate level of anaesthesia. BIS was measured using an BIS EEG monitor (Asp ect A 2000, Aspect Medical Systems Inc., Natick, MA, USA). Results: We found no significant difference between BIS scores in anaesthet ized pigs with I MAC of halothane or 70% xenon or in total intravenous anae sthesia. In addition, we found no significant difference in BIS during the whole anaesthesia with halothane or xenon. BIS levels during halothane and xenon anaesthesia were comparable to those measured under TIVA and surgical preparation. BIS values remained unchanged during xenon anaesthesis as com pared with TIVA and halothane anaesthesia. Conclusion: As a conclusion the BIS EEG is a very promising tool for measur ing depth of xenon, halothane and total intravenous anaesthesia also in ani mals.