Research project
One of the projects supported by funds from the Caring for Pets Program was “Cause and management of hypotension in anaesthetised horses”.
Anaesthesia of healthy horses for elective procedures is associated with a higher frequency of complications than any other species. One of the most common complications is low blood pressure which can lead to muscle damage that can be so severe as to warrant euthanasia. As a result measurement and treatment of blood pressure in anaesthetised horses is routinely performed.
The most common treatment used to correct blood pressure is a drug called dobutamine, which is believed to increase blood pressure by improving the function of the heart. Recent published work has raised questions over the effectiveness of this drug when different combinations of drugs are used for sedation and anaesthesia of horses.
The purpose of the study funded was to determine if different combinations of sedatives altered the effect of dobutamine on heart function. This resulted in four groups of horses:
1. Sedated with xylazine alone prior anaesthesia
2. Sedated with acepromazine and xylazine
3. Sedated with romifidine alone prior anaesthesia
4. Sedated with acepromazine and romifidine
A total of 40 horses were recruited into the study. Of these, 27 horses developed low blood pressure requiring dobutamine administration. In all groups dobutamine increased blood pressure, but this was only accompanied by an increase in heart function in the group that received acepromazine and romifidine prior to anaesthesia. In all other groups heart function did not change and tended to decrease. Despite this none of the horses suffered any post-operative complication.
These results confirm that drugs used to improve heart function and blood pressure can be altered by the choice of sedation and anaesthetic agent. Although none of the horses suffered any ill effects in this study, it is clear that certain drug combinations have a beneficial effect on heart function and how it responds to dobutamine.
This knowledge can help vets make better choices when planning anaesthetic protocols and hopefully continue to reduce the risk associated with routine anaesthesia in horses.