Читать книгу Complications in Equine Surgery - Группа авторов - Страница 214

Ketamine is a dissociative anesthetic with actions on several receptors, but the antagonism of the N‐methyl‐D‐aspartate (NMDA) receptors in the central nervous system (CNS) is mainly responsible for its anesthetic, analgesic, psychotomimetic and neuroprotective effects. It is widely used in horses in combination with benzodiazepines and/or alpha‐2 adrenergic agonists as an induction agent and in total intravenous anesthesia, producing rapid and smooth induction with minimal cardiovascular depression and good analgesia. Intraoperative constant rate infusions (CRI) of ketamine are used in equine anesthesia as part of the balanced anesthesia concept aiming to improve analgesia, reduce the amount of inhaled agent and preserve cardiovascular function [19].

It seems that recovery from ketamine anesthesia in the horse depends on rapid redistribution of the drug from the central compartment and this explains the abrupt recovery from ketamine anesthesia often observed in the horse.

The exact dose or circulating concentration of ketamine at which excitement or abnormal behavior occurs may vary between horses and has not been identified. Fielding et al. [29] concluded in their study that the use of subanesthetic doses of ketamine in standing horses up to 0.8 mg/kg/h for 6 hours did not cause signs of excitement, but an analgesic effect was not obtained with the method of analgesic testing used.