Evaluation of the local analgesic effect of ketamine in the palmar digital nerve block at the base of the proximal sesamoid (abaxial sesamoid block) in horses.

This research tests the pain-relieving properties of ketamine in horses when applied as a local nerve block at the base of the hoof. The study shows that injecting ketamine leads to a significant reduction of pain response within two to fifteen minutes after application.

Study Design and Methodology

• The research involved 36 healthy mature Andalusian horses, which were randomly assigned to four different study groups, each consisting of nine horses.
• The horses in each group were given a local abaxial sesamoid block on a randomly selected front leg using varying strengths of solution: saline (0.9% NaCl), 1% ketamine, 2% ketamine, or 3% ketamine.
• To measure pain response, the team used a model that entailed exposing the horse’s hoof to radiant heat and recording the time it took for the horse to withdraw its hoof – a model known as the “radiant heat lamp-hoof withdrawal model”.
• Before the nerve block application, the team recorded a baseline hoof withdrawal reflex latency (HWRL – the time taken for the horse to withdraw its hoof from the heat source). Following the nerve block, they measured the HWRL at regular intervals for one hour, to assess the analgesic effects of the treatments.

Key Findings

• The research found that there were marked differences in HWRL values between the baseline and the period two to fifteen minutes following the nerve block with ketamine, implying a significant reduction in pain response.
• The results also showed that there were marked differences in HWRL values when comparing readings from two to ten minutes following a saline-based nerve block, against those from a 1 or 2% ketamine nerve block. This suggests that the 1 and 2% ketamine blocks were more effective in reducing pain during this period.
• The 3% ketamine solution induced a more significant effect on HWRL values when compared to the saline-based solution, causing noticeable differences from two to fifteen minutes following the nerve block. This difference points towards a more extended pain-reducing effect with the strongest ketamine concentration.

Conclusion

• The research concludes that an abaxial sesamoid block with ketamine results in effective pain relief in horses, with the analgesic effects setting in within two minutes and lasting for up to fifteen minutes.