Effects of a constant-rate infusion of dexmedetomidine on the minimal alveolar concentration of sevoflurane in ponies.

The study examines the effects of administering dexmedetomidine at a steady rate on the minimal alveolar concentration (MAC) of sevoflurane anesthesia in ponies, discovering that it significantly decreases the MAC.

Objective and Methods

• The primary objective of the research was to assess the effects a constant-rate infusion (CRI) of dexmedetomidine, a sedative, has on the required amount (MAC) of sevoflurane, an inhalation anaesthetic, in ponies. Earlier studies had demonstrated that dexmedetomidine helped to spare the use of inhalant anaesthetics in different species, but this effect hadn’t been tested in horses.
• The experiment was conducted under a randomized, crossover, blinded experimental design. Six healthy adult ponies were used, each undergoing two anaesthesia sessions with a three-week ‘washout’ period in between to eliminate residual drug effects.
• The ponies were induced with sevoflurane through a nasotracheal tube and then maintained on a 2.5% sevoflurane composition in 55% oxygen. After being positioned on a surgical table, they were either given dexmedetomidine (treatment D) or saline (treatment S).
• The MAC was determined using a classic bracketing technique after 60 minutes, involving electrical stimuli at the pony’s skin. The MAC estimations taken were triplicate and then averaged. The ponies were continuously monitored using a range of techniques including pulse oximetry, electrocardiography, anaesthetic gas monitoring, arterial blood pressure measurement, and arterial blood gas measures. Mechanical ventilation was applied to maintain normocapnia.

Results and Conclusions

• The results demonstrated that a dexmedetomidine CRI effectively reduced the average sevoflurane MAC by 53 ± 15%, from 2.42 ± 0.55% to 1.07 ± 0.21%. In essence, using dexmedetomidine means lesser sevoflurane is needed to achieve the same effect.
• Based on these findings, the authors conclude that using a dexmedetomidine CRI at the doses tested in the study significantly reduces the MAC of sevoflurane in ponies. This conclusion offers impactful implications for using dexmedetomidine during inhalation anaesthesia in veterinary medicine, noting its significant ability to decrease the amount of potentially harmful inhalation anaesthetic required.