Evaluation of the bispectral index as an indicator of degree of central nervous system depression in isoflurane-anesthetized horses.

This research attempted to find out whether the bispectral index (BIS), a calculation derived from electroencephalographic (EEG) data, can be used as a measure of CNS (central nervous system) depression in horses anesthetized with isoflurane. However, the study found that BIS is not a precise measure for this purpose.

Methodology

Here’s a breakdown of the research methodology:

• 16 horses, both Standardbred and Norwegian cold-blooded trotters, were used in the experiment.
• An EEG monitor recorded brain activity before and after the horses were given detomidine and butorphanol, both sedatives.
• Anesthesia was induced with ketamine hydrochloride and diazepam, then maintained with isoflurane in oxygen.
• The BIS was calculated again after 30 minutes and during surgery.
• One group of eight horses had an end-tidal isoflurane concentration of 1.4%, and the other group had a concentration of 1.9%. This difference in concentration was to see if it affected the BIS.

Results

The findings of the experiment were:

• The BIS decreased significantly when the horses were sedated and anesthetized, compared to their awake state.
• However, the BIS did not change significantly between sedated and anesthetized horses.
• The mean BIS in horses anesthetized at 1.9% isoflurane was higher than that of horses at 1.4% isoflurane concentration.
• Four horses in the 1.4% group moved during surgery. Two of those horses showed increases in BIS before they moved.

Conclusions

The study concluded that the BIS is not an accurate indicator of CNS depression in horses anesthetized with isoflurane. As such, it may not be a suitable technique for monitoring anesthetic depth during surgery on isoflurane-anesthetized horses. The usual changes in BIS seen with sedation and anesthesia didn’t apply as expected. Also, varying the isoflurane concentration had a more significant impact on the BIS than initially thought. So, more investigation is required to determine exactly how and why BIS readings change during anesthesia.