Effects of epidural administration of dexmedetomidine on the minimum alveolar concentration of isoflurane in dogs

Abstract

Objective-To evaluate the effects of epidural administration of 3 doses of dexmedetomidine on isoflurane minimum alveolar concentration (MAC) and characterize changes in bispectral index (BIS) induced by nociceptive stimulation used for MAC determination in dogs. Animals-6 adult dogs. Procedures-Isoflurane-anesthetized dogs received physiologic saline (0.9% NaCl) solution (control treatment) or dexmedetomidine (1.5 [DEX1.5], 3.0 [DEX3], or 6.0 [DEX6] mug/kg) epidurally in a crossover study. Isoflurane MAC (determined by use of electrical nociceptive stimulation of the hind limb) was targeted to be accomplished at 2 and 4.5 hours. Changes in BIS attributable to nociceptive stimulation and cardiopulmonary data were recorded at each MAC determination. Results-With the control treatment, mean +/- SD MAC values did not change over time (1.57 +/- 0.23% and 1.55 +/- 0.25% at 2 and 4.5 hours, respectively). Compared with the control treatment, MAC was significantly lower at 2 hours (13% reduction) but not at 4.5 hours (7% reduction) in DEX1.5-treated dogs and significantly lower at 2 hours (29% reduction) and 4.5 hours (13% reduction) in DEX3-treated dogs. The DEX6 treatment yielded the greatest MAC reduction (31% and 22% at 2 and 4.5 hours, respectively). During all treatments, noxious stimulation increased BIS; but changes in BIS were correlated with increases in electromyographic activity. Conclusions and Clinical Relevance-In dogs, epidural administration of dexmedetomidine resulted in dose-dependent decreases in isoflurane MAC and that effect decreased over time. Changes in BIS during MAC determinations may not represent increased awareness because of the possible interference of electromyographic activity.

Lidocaine, Dexmedetomidine and Their Combination Reduce Isoflurane Minimum Alveolar Concentration in Dogs

“…In addition, the combination LIDO-DEX produced a greater effect than the two drugs alone, in accordance with the hypothesis of this study. The range of MAC values reported here for isoflurane (1.28–1.58%) was similar to that shown in previous studies (1.34–1.57%) [2], [3], [4], [17]. One reason for small discrepancies among MAC studies is subjectivity in the interpretation regarding what constitutes movement after the application of a noxious stimulus.…”

“…This finding may be related to significantly decreased isoflurane concentrations, as reported previously [3], [7]. The dosage regimens reported here are commonly used during surgery in dogs when the provision of analgesia, sedation and limitation of the stress response is required [6], [11], [17].…”

“…DEX is widely used in small animal anaesthesia to provide sedation, anxiolysis and analgesia [6]. DEX bolus, CRI and epidural administration has been shown to reduce the anaesthetic requirement for the induction and maintenance of general anaesthesia in dogs [4], [6], [17]. To the best of our knowledge, the effect of a LIDO-DEX combination administered by bolus followed by CRI on the MAC ISO has not been reported in dogs.…”

An Update on Drugs Used for Lumbosacral Epidural Anesthesia and Analgesia in Dogs

“…Epidural dexmedetomidine (1 μg kg −1 ), the active isomer of medetomidine with a high alpha 2 -selectivity and efficacy, produced an antinociceptive effect and reduced heart rate, without changes in carbon dioxide response, behavior, and motor function (110). Epidural administration of dexmedetomidine to isoflurane-anesthetized dogs decreased the MAC of the inhalant anesthetic in a dose-dependent fashion (111). …”

Effects of Lidocaine, Dexmedetomidine or Their Combination on the Minimum Alveolar Concentration of Sevoflurane in Dogs

“…Studies in humans and in dogs suggest that low doses of alpha 2 -adrenergic agonists may produce the sparing effects of anesthetic requirements and analgesia with minimal impact on cardiovascular function [1,2,3, 24]. In dogs, dexmedetomidine has been shown to reduce the anesthetic requirement for induction and maintenance of general anesthesia [2, 8, 24, 34]. Therefore, it is expected that the balanced anesthesia using a combination of lidocaine and dexmedetomidine infusion may decrease sevoflurane requirement and therefore may reduce the incidence of its side effects.…”