Abstract
BackgroundAlfaxalone has a number of pharmacological properties which are desirable for constant rate infusion (CRI). Previously, the co-administration of alfaxalone and medetomidine is shown to be suitable for short-term anesthesia in horses. However, the use of alfaxalone–medetomidine CRI with inhalational anesthesia under surgical procedures have not been investigated in clinical cases. The aim of the present study was to evaluate the clinical efficacy of alfaxalone–medetomidine CRI in sevoflurane-anesthetized Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane requirement, cardiovascular function, and induction/recovery quality were compared between horses maintained with sevoflurane in combination with medetomidine CRI (3 µg/kg/h) (Group M; n = 25) and those maintained with sevoflurane in combination with alfaxalone–medetomidine CRI (0.5 mg/kg/h and 3 µg/kg/h, respectively) (Group AM; n = 25).ResultsThe mean end-tidal sevoflurane concentrations were significantly lower in Group AM (1.8 ± 0.2%) than in Group M (2.4 ± 0.1%). The mean dobutamine infusion rate required for maintaining mean arterial blood pressure within the target values (60–80 mmHg) was significantly lower in Group AM (0.53 ± 0.20 µg/kg/min) than in Group M (0.85 ± 0.32 µg/kg/min). Induction and recovery scores were not significantly different between two groups. However, excitatory response during recovery were observed in five horses in Group AM. The mean plasma alfaxalone concentrations were stable throughout the maintenance period (0.77 ± 0.12 to 0.85 ± 0.13 µg/mL), and decreased significantly immediately after standing (0.32 ± 0.07 µg/mL).ConclusionsAlfaxalone–medetomidine CRI reduced sevoflurane requirement by approximately 26% with good maintenance of cardiopulmonary function in Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane in combination with alfaxalone–medetomidine CRI may be a clinically effective anesthetic technique for Thoroughbred racehorses. However, 20% of horses administered alfaxalone showed remarkable excitatory response during recovery. Greater attention to excitatory response may be advisable if alfaxalone is used for induction or maintenance of anesthesia. A larger study is needed to explore the clinical relevance of these findings.
Highlights
Alfaxalone has a number of pharmacological properties which are desirable for constant rate infu‐ sion (CRI)
We found that medetomidine CRI (3.0 μg/kg/h) reduced the sevoflurane requirement for arthroscopic surgery by approximately 10% in Thoroughbred racehorses, resulting in good maintenance of cardiopulmonary function, and an improvement in the quality of recovery from anesthesia [13]
The cardiovascular parameters heart rate (HR), systolic arterial blood pressure (SAP), diastolic arterial blood pressure (DAP), and mean arterial blood pressure (MAP) did not change significantly throughout the maintenance, and there were no significant differences between the two groups (Table 1)
Summary
Alfaxalone has a number of pharmacological properties which are desirable for constant rate infu‐ sion (CRI). Balanced anesthesia is often used to reduce the requirements of inhalation anesthetics and to thereby minimize their cardiovascular depressant effects in equine practice [8]. Most balanced anesthetic protocols include the use of an α2-adrenoceptor agonist because of their potent sedative and analgesic effects [8] One such α2-adrenoceptor agonist is medetomidine, whose short half-life, selectivity, and potency make it suitable for use as a constant rate infusion (CRI) for balanced anesthesia in horses [9,10,11,12]. We found that medetomidine CRI (3.0 μg/kg/h) reduced the sevoflurane requirement for arthroscopic surgery by approximately 10% in Thoroughbred racehorses, resulting in good maintenance of cardiopulmonary function, and an improvement in the quality of recovery from anesthesia [13]. The anesthetic sparing effect of medetomidine CRI on sevoflurane was insufficient to minimize the negative cardiovascular effects of sevoflurane, and cardiovascular depression during the maintenance period still remained a concern
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