Effect of ketamine on the limb withdrawal reflex evoked by transcutaneous electrical stimulation in ponies anaesthetised with isoflurane.

The research investigates the pain-relieving effects of ketamine combined with isoflurane using a limb withdrawal reflex test on sedated horses. Results indicate that ketamine increased the threshold of stimulation needed for a reflex and decreased the response amplitude in a dose-dependent manner, demonstrating its potential use in controlling pain during veterinary procedures.

Objective of the Research

• The primary aim of this study was to assess the pain-relieving (anti-nociceptive) activity of ketamine, a well-known anaesthetic and pain control agent, in combination with isoflurane, another commonly used anaesthetic, in horses.
• The researchers used a limb withdrawal reflex (WR) model as a proxy to gauge the level of discomfort or pain experienced by the animals.

Methodology

• Electrical stimulations were repeatedly applied to the nerves of the left forelimb in ponies, which were sedated using isoflurane. The stimulations were applied before, during, and after the intravenous administration of ketamine.
• The muscle activity was measured using surface Electromyography (EMG), a technique that records electrical activity produced by muscles, from the deltoid muscle – a large muscle responsible for lifting the arm.

Findings

• The observation indicated that higher stimulation intensity was required to trigger a reflex reaction during the administration of ketamine, suggesting that ketamine increases the pain threshold.
• The study also found that ketamine caused a significant and dose-dependent decrease in the amplitude of response to the stimulations. This implicates that ketamine can suppress the intensity of the pain response.
• The results revealed a flattening of the stimulus-response curves during the ketamine application, which means the reflex activity became more stable or reduced during this period. However, the reflex activity partially recovered once the ketamine administration was stopped, indicating that the effects of ketamine are not permanent.

Conclusion

• From the investigation, it was concluded that the limb withdrawal reflex can be used effectively to measure the timing and intensity of the pain-relieving effects of ketamine on horses sedated with isoflurane.
• This research provides an important insight into the veterinary use of ketamine and can facilitate better pain management in procedures involving the use of isoflurane as an anaesthetic.