Comparison of midazolam and diazepam as co-induction agents with ketamine for anaesthesia in sedated ponies undergoing field castration.

This study compares the effects of two anaesthetics, midazolam and diazepam, when used together with ketamine to induce anaesthesia in ponies that are undergoing field castration. The results indicate that both drugs can be used interchangeably for this purpose without significant differences in the observed outcomes.

Research Design and Methods

• The study is a prospective, randomised, clinical study which is also ‘blinded’, meaning that the observers scoring the effects of the anaesthetics did not know which treatment each pony received.
• Twenty Welsh pony yearlings were involved in the study. The ponies had already been sedated with detomidine, then they were given either midazolam (group M) or diazepam (group D), along with ketamine to induce anaesthesia.
• Induction of anaesthesia, sedation quality, the ability to intubate, surgery conditions and the recovery process were all scored by the observers. The timings of anaesthesia and surgery-related events were also recorded.
• The study also monitored cardiorespiratory function at intervals of 5 minutes, and noted additional requirements of ketamine, if any, and any other adverse effects.
• The researchers analysed the data using statistical methods including two-way anova, unpaired t-tests and Mann-Whitney U tests as required. Significance level was set at p < 0.05, meaning that any results with a probability less than 5% of occurring by chance were considered significant.

Results of the Study

• There were no significant differences between the two treatment groups in any of the assessed variables, apart from bodyweight; group M ponies were slightly heavier on average than those in group D.
• One pony in group M needed extra ketamine 15 minutes after the anaesthesia was induced.
• Surgical conditions were considered good in all cases, and there were no adverse effects noted. The time taken for the animals to regain standing position after anaesthesia induction was similar between the groups.
• The recovery process was smooth with minimal ataxia – a lack of voluntary coordination of muscle movements.

Conclusions

• The findings suggest that both midazolam and diazepam can be used in combination with ketamine to safely induce short-term anaesthesia in ponies that are already sedated with detomidine.