Effects of midazolam and sarmazenil on the equine electroencephalogram during anaesthesia with halothane in oxygen.

This research study investigates the impact of two drugs, midazolam and sarmazenil, on the brain activity of anaesthetized ponies, as recorded via an electroencephalograph (EEG). The results revealed that midazolam caused significant changes in the EEG records, which were then reversed by sarmazenil, suggesting that sarmazenil does not affect the EEG independently.

Introduction and Methodology

• The study focused on examining the effects of midazolam (a sedative) and sarmazenil (a benzodiazepine antagonist), on the EEG during anaesthesia with halothane (an inhalational anaesthetic) in oxygen. This was conducted on eight Welsh mountain ponies.
• The drugs were administered as a rapid infusion, with midazolam injected first followed by sarmazenil. The researchers determined the plasma concentration of midazolam five minutes after the infusion started, however, they did not measure sarmazenil concentrations.

Result Highlights

• The peak plasma concentration of midazolam reached 2.13 +/- 0.34 ng/mL.
• The 95% spectral edge frequency of the EEG, which shows the frequency below which the majority of the power in the signal resides, reduced significantly, by up to 39.8 +/- 15.8%, 10 minutes after the start of the midazolam infusion.
• No changes were noted in the median frequency of the EEG or the second differential of the middle latency auditory evoked response, a measure of sound-processing speed.
• The variability of the median frequency and the spectral edge frequency dropped by a significant 80 +/- 7 and 84 +/- 7% respectively.

Impact of Sarmazenil Infusion

• The infusion of sarmazenil reversed the effects of midazolam on the variability of the median frequency and the magnitude and variability of the 95% spectral edge frequency.
• The second differential of the middle latency auditory evoked potential increased significantly, by 56.4 +/- 69.3%, 10 minutes after the sarmazenil infusion began.
• However, the differences in EEG variables between the baseline of the midazolam infusion and 10 minutes after the sarmazenil infusion began were not statistically significant.

Conclusion

• The study concluded that a midazolam infusion introduces specific and unique changes in the EEG of anesthetized ponies, which sarmazenil could then reverse fully. Moreover, the research suggests that sarmazenil has no independent impact on the EEG.