Effects of ketamine on the equine electroencephalogram during anesthesia with halothane in oxygen.

The research study explores the impact of ketamine on the electroencephalographic patterns in horses during anesthesia with halothane in oxygen. The findings highlight that the infusion of ketamine caused a significant shift in the spectral edge frequency, suggesting its utility as a measure of central nervous system depression.

Methods

• The study was designed as a prospective experimental study centered around 8 Welsh mountain pony geldings, aged between 5 and 9 years.
• Under halothane anesthesia maintaining end tidal halothane concentration between 0.75 and 0.85%, the researchers recorded the EEG frequency power spectrum and the auditory evoked potential of the horses.
• Ketamine, in a dosage of 200 mg, was infused over 5 minutes in all of the horses.
• The study continuously recorded the effects of ketamine on the EEG during the infusion and for an additional 55 minutes.

Results

• The ketamine infusion lead to a plasma ketamine concentration that was notably greater than the baseline for up to 7 minutes post the start of the infusion.
• The maximum ketamine concentration registered was 4.2+/-1.1 microg/ml, observed at 5 minutes after the beginning of the infusion.
• The researchers then compared the spectral edge and median frequency of the EEG and the midlatency of the auditory evoked potential with those recorded prior to the start of the infusion.
• They observed reductions in the spectral edge, median frequencies and mid-latency of the auditory evoked potential by 21+/-13%, 31+/-20% and 19+/-36% respectively.
• However, it is important to note that the shift in spectral edge frequency was the only change which achieved statistical significance.

Conclusions

• Comparing these results with those from other anesthetic and sedative agents led to the conclusion that the spectral edge frequency could demonstrate general central nervous system depression.
• Conversely, the median frequency might be indicative of antinociception, potentially pointing towards pain relief.

These findings could have implications for identifying effective anesthesia strategies in equine medicine, allowing for improved understanding of anesthetic effects on brain activity, and potentially guiding future anesthetic management in horses.