Comparison of ketamine and S(+)-ketamine, with romifidine and diazepam, for total intravenous anesthesia in horses.

The study compares two forms of ketamine used in total intravenous anesthesia of horses, attempting to understand the differences in terms of muscle relaxation, potency, and its effects on the heart and lungs. The researchers found that both types of ketamine largely had the same effects on the horses’ bodies during anesthesia. However, one form, S(+)-ketamine, required fewer maintenance doses and resulted in a better recovery after anaesthesia.

Study Design

• The study was a prospective randomized clinical trial involving 16 healthy stallions aged around 6.2 years, where each horse was randomly assigned to receive either ketamine or S(+)-ketamine with romifidine and diazepam.
• The horses were pre-medicated with romifidine intravenously, 15 minutes prior to induction of anesthesia. Following this, they received either a diazepam-ketamine or diazepam-S(+)-ketamine mixture at similar doses to induce anaesthesia.
• The duration from induction to lateral recumbency, first additional dose requirement, return to sternal posture and time to standing were recorded to evaluate the quality of induction, muscle relaxation and recovery.

Results

• Both forms of ketamine – racemic and S(+)- – resulted in similar induction quality and duration of anesthesia, with no significant differences between heart rate, respiratory rate, and systolic blood pressure.
• While some horses showed minor excitatory effects during induction with the diazepam S(+)-ketamine mixture, fewer maintenance doses were needed for these animals, and their recovery scores were better ranked compared to those using the other type of ketamine.

Conclusions

• The findings suggest that S(+)-ketamine has some advantages over racemic ketamine, including less anesthetic agent required for maintenance, and a better overall recovery post-anesthesia.
• While these results provide insight, the authors agree that further studies are needed to determine the optimal induction dose of S(+)-ketamine in this context.