Safety of equine anaesthesia could be improved

A considerable number of unwanted adverse effects are associated with sedating and anaesthetising horses. Promising results were gained in a study completed at the University of Helsinki by using vatinoxan, a tranquilliser antagonist, when sedating horses.

One of the special characteristics of horses, namely their large size, causes circulatory disturbances during anaesthesia. Under anaesthesia, horses’ blood pressure also easily drops, further weakening circulation through tissues. Tranquillisers alter the functioning of the cardiovascular system, suppress intestinal motility and elevate blood glucose levels. Indeed, complications are more prevalent and the mortality rate higher in equine general anaesthesia compared to many other animal species.

In her doctoral dissertation, Soile Pakkanen looked into the effects of vatinoxan on tranquillised and anaesthetised horses. Vatinoxan is an antagonist of the most common equine tranquillisers, previously found to alleviate their unwanted effects in other species. However, vatinoxan does not cross the blood-brain barrier to a significant degree, thus avoiding reversals in the sedating effect achieved with tranquillisers.

“The findings indicate that combining vatinoxan with tranquillisers when sedating horses could reduce or even prevent the occurrence of the undesired effects of tranquillisers,” Pakkanen says. 

During the study, horses were administered tranquillisers and vatinoxan in different combinations. In addition, vatinoxan was administered as part of the preanaesthetics before general anaesthesia. The medicated horses were monitored for the functioning of the cardiovascular system and intestinal sounds, while blood samples were used to measure, among other factors, blood gases, blood glucose and drug concentrations in blood. 

Vatinoxan significantly alleviated effects caused by tranquillisers, such as a drop in the heart rate, changes in blood pressure, decreases in intestinal motility and increased blood glucose levels. At the same time, no clinically significant changes were observed in the sedation of the horses. 

Instead, used as a preanaesthetic, vatinoxan caused a notable drop in blood pressure, even though heart function and the oxygen-carrying capacity of blood appeared to improve. Vatinoxan was also found to have an effect on the concentration and behaviour of drugs in the equine body.

“Further studies on using vatinoxan in conjunction with general anaesthesia must be carried out to determine whether excessive drops in blood pressure can be prevented, for example, with lower doses of vatinoxan. Furthermore, the agent is yet to be registered as a veterinary medicinal product, but it’s in the process, and we are hopeful that it would get in the market in the coming years,” Pakkanen notes. 

Doctoral dissertation: 

Veterinarian Soile Pakkanen will defend her doctoral dissertation entitled "Interaction of alpha-2-adrenoceptor agonists and vatinoxan, a peripherally acting alpha-2-adrenoceptor antagonist, in horses” in the Faculty of Veterinary Medicine, University of Helsinki, on 22 March 2019 at 12.00. The public defence will take place at Clinicum, lecture room Paatsama, Koetilankuja 4.

Professor Görel Nyman from the Swedish University of Agricultural Sciences will serve as the opponent and Professor Outi Vainio as the custos.