The pre-emptive effect of epidural ketamine on wound sensitivity in horses tested by using von Frey filaments.

The research study evaluates the analgesic effect of epidural ketamine administered before an incision in horses. The application of the drug showed promising results in reducing post-operative pain.

Participants and Methodology

• The study engaged 16 mixed breed mares, aged around 7.6 years and weighing approximately 352 kg. These horses were randomly divided into two groups, group A (ketamine, n=9), and group B (saline, n=7).
• A pilot study was first conducted where an incision was made on one side of the thigh of a horse using a lidocaine block and not using any further analgesics to establish that the pain threshold was lower on the incised side than the non-incised side. This study also confirmed that von Frey filaments can invoke a pain response.
• An epidural catheter was inserted into the subjects 24 hours prior to the trials. The thigh was shaven bilaterally and blocked (incised side) using lidocaine.
• After 25 minutes, either ketamine (for group A) or saline (for group B) was administered epidurally. Following five minutes, a skin incision of length 10-cm was made, the incised side was then sutured.

Measuring the Nociceptive Threshold

• Nociceptive threshold or the level of stimulus needed to induce pain was determined using von Frey filaments at 1, 3, and 5 cm distances around the incision at 15-minute intervals for 2 hours, and then after that at 4, 6, and 8 hours.
• The researchers also monitored changes in behavior, heart rate, and respiratory rate of the horses, along with calculating averaged nociceptive thresholds to get mean values at each time.
• The gathered data were then analyzed on a logarithmic scale using nonparametric statistical methods, including the Mann-Whitney test and one-way repeated measures ANOVA test.

Results and Conclusion

• By the end of 8 hours, the global range score revealed a significant decrease (P<0.01) in wound sensitivity around the incision in about 92% of the evaluated time intervals for the ketamine group.
• The group that received the ketamine injection before the incision did not exhibit any significant alterations in behavior, heart rate, and respiratory rate.
• From the recorded results, the research team concluded that pre-emptive administration of epidural ketamine indeed reduces post-operative pain in horses.
• The study also endorsed that von Frey filaments can effectively quantify cutaneous sensitivity after tissue damage in horses.