The bispectral index during recovery from halothane and sevoflurane anaesthesia in horses.

This study investigates the use of the bispectral index (BIS) for monitoring horse consciousness during recovery from two different types of anaesthesia, halothane and sevoflurane. It also considers the association of BIS with unexpected movement during surgery and consciousness-related movement during recovery.

Research Methodology

• 25 horses were included in this randomized prospective clinical study. These horses were undergoing surgery, aged between 1 to 19 years, with an average age of 8.8 years.
• The horses were classified into two groups, one group to receive halothane anaesthesia (n = 12) and the other to receive sevoflurane (n = 13), with BIS values recorded at several stages during the process.
• Baseline BIS values were noted before the administration of pre-anaesthetic medication. Furthermore, BIS values were also recorded during anaesthesia, during surgery if any unexpected movement occurred, during recovery at the time of the first consciousness-linked movement, and once sternal recumbency (lying down on the chest) was achieved.

Research Findings

• No significant difference was found in BIS scores at the first movement linked to consciousness between the two anaesthesia types, halothane and sevoflurane. However, while the horses were under anaesthesia, the BIS scores of the sevoflurane group were significantly lower than those of the halothane group.
• The difference between anaesthesia BIS scores and those at the first consciousness-linked movement was significant and greater in the sevoflurane group compared to the halothane group.
• In more than half of the horses, BIS values during unexpected movement during surgery were somewhere between the scores during anaesthesia and at the first movement during recovery.

Conclusions

• The findings suggest that BIS may be a useful tool for approximating levels of unconsciousness and hence assist with equine anaesthesia monitoring. The BIS values appear to correlate with the difference in unconsciousness levels between the two types of anaesthesia used.
• However, the BIS does not seem to effectively predict intra-operative movement, as the scores during unexpected movement tended to range between those observed during anaesthesia and conscious recovery.