Balanced Anesthesia in the Equine

Abstract

The following article aims at giving an overview on currently available balanced anesthetic regimens for horses. In horses, maintenance of cardiovascular function and thus muscular perfusion during anesthesia is essential. Also, a smooth recovery phase which should be completed within at least 1 hour of termination of drug administration is crucial. All inhalation anesthetics depress cardiovascular function dose dependently. Thus, drugs that decrease the need for inhalation anesthetics (decrease MAC) might improve cardiovascular function during anesthesia. Lidocaine constant rate infusion (CRI), at clinically used dose rates, decreases MAC by about 25%, and no untoward cardiovascular side effects have been reported. In horses anesthetized for several hours, careful dosing is advised. Toxicity due to accumulation, masked during anesthesia, might become apparent during recovery. Ketamine is the only drug used for balanced anesthesia that might positively influence cardiovascular function. But following continuous ketamine administration for longer time periods (>2 hours), rough recoveries can occur. Preliminary results with S-ketamine CRIs showed better results in this respect, but further studies are warranted. Medetomidine CRI does decrease MAC about 30% at recommended dose rates. Cardiovascular function in comparison to lidocaine balance is moderately impaired, but horses show less intraoperative awakening following surgical stimulation. Recovery phase following medetomidine balance is clearly smoother than with any other regimen. In conclusion, lidocaine, ketamine, and medetomidine are mainly used for balanced anesthesia in horses. In cardiovascularly compromised patients, ketamine might be advantageous. If a smooth recovery phase is crucial, medetomidine should be the drug of choice.