Abstract
Simple SummaryHistorically, the use of opioids in equine anaesthesia has been limited due to many reported adverse effects. Even though more research is being conducted, there is conflicting evidence on the efficacy of opioids and their behavioural effects in horses. The aim of this study was to investigate the effect of the synthetic opioid fentanyl on various parameters measured during general anaesthesia, as well as to determine its possible sparing-effect on inhalant anaesthetic.Controversy continues to surround the use of opioids in equine anaesthesia, with variable effects reported. This blinded clinical study aimed to investigate the influence of a low-dose fentanyl continuous rate infusion (CRI) on isoflurane requirements, parasympathetic tone activity (PTA), and anaesthetic parameters in horses during general anaesthesia. All of the twenty-two horses included in the research underwent a standard anaesthetic protocol. Eleven horses in the fentanyl group (Group F) received a loading dose of fentanyl at 6 µg/kg, followed by a CRI of 0.1 µg/kg/min during anaesthesia. A further 11 horses in the control group (Group C) received equivalent volumes of normal saline. Anaesthetic parameters and PTA index were recorded during anaesthesia. The achieved mean fentanyl plasma concentration was 6.2 ± 0.83 ng/mL. No statistically significant differences between groups were found in isoflurane requirements, MAP values, and mean dobutamine requirements. However, horses in Group F required a significantly lower dose of additional ketamine to maintain a sufficient depth of anaesthesia. Significantly higher PTA values were found in the fentanyl group. Further research is warranted to determine the limitations of PTA monitoring, and the influence of various anaesthetics on its values.
Highlights
Opioids are commonly used in numerous animal species, often as a part of balanced anaesthesia protocols, where their analgesic and sedative effects reduce the requirement for other anaesthetic agents [1]
Horses were included in the study if their American Society of Anesthesiologists (ASA) physical status was I-III based on medical history, clinical examination and routine pre-anaesthetic blood analysis
Eleven horses were recruited in the fentanyl group
Summary
Opioids are commonly used in numerous animal species, often as a part of balanced anaesthesia protocols, where their analgesic and sedative effects reduce the requirement for other anaesthetic agents [1]. Horses have been known to respond to opioids with excitement and increased locomotor activity (probably a consequence of central nervous system excitation), and a decrease in gastrointestinal motility. It seems that the magnitude of these side effects is related to the drug and dose administered, as well as to an individual sensibility. A recent study showed that increased locomotor activity is probably related to G57C μ-opioid receptor polymorphism, expressed in heterozygous animals [8]. There seems to be a narrow therapeutic margin between the doses required to produce analgesia and excitation [1], which prompts further research to find precise doses for each opioid receptor agonist
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