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

Introduction: Bispectral index (BIS) is a promising method for monitoring anaesthetic depth in humans. Inhalational and intravenous anaesthetics produce 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 halothane, isoflurane, desflurane and sevoflurane and plasma propofol concentrations have been reported in several investigations. We have investigated the effect of xenon anaesthesia on bispectral index (BIS) in pigs. Materials and Methods: BIS index was measured under total intravenous, xenon and halothane anaesthesia: in 8 pigs. Each animal received 1 MAC halothane before or after xenon anaesthesia in randomized cross over design to eliminate systemic errors. Between xenon and halothane anaesthesia total intravenous anaesthesia was applied to eliminate the effects of the anaesthetic gas first applied. Surgical stimuli were not present during xenon and halothane anaesthesia, surgical preparations were completed in TIVA. BIS levels measured during preparation phase were used as reference values to assure adequate level of anaesthesia. BIS was measured using an BIS EEG monitor (Aspect A 2000, Aspect Medical Systems Inc., Natick, MA, USA). Results: We found no significant difference between BIS scores in anaesthetized pigs with I MAC of halothane or 70% xenon or in total intravenous anaesthesia. 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 compared with TIVA and halothane anaesthesia. Conclusion: As a conclusion the BIS EEG is a very promising tool for measuring depth of xenon, halothane and total intravenous anaesthesia also in animals.