Comparison of the effects of xylazine bolus versus medetomidine constant rate infusion on the stress response, urine production, and anesthetic recovery characteristics in horses anesthetized with isoflurane

Abstract

Objective—To compare the effect of xylazine bolus versus medetomidine constant rate infusion (MCRI) on serum cortisol and glucose concentrations, urine production, and anesthetic recovery characteristics in dorsally recumbent, spontaneously breathing, isoflurane-anesthetized horses. Design—Prospective, randomized crossover study. Animals—10 healthy Standardbreds. Procedures—Horses were premedicated with xylazine or medetomidine IV. Anesthesia was induced with diazepam and ketamine and maintained with isoflurane for 150 minutes. For the xylazine treatment, end-tidal isoflurane concentration was maintained at 1.7% and xylazine (0.2 mg/kg [0.09 mg/lb]), IV) was administered as a bolus at the end of anesthesia. For the MCRI treatment, end-tidal isoflurane concentration was maintained at 1.4% and medetomidine (0.005 mg/kg/h [0.0023 mg/lb/h], IV) was infused throughout anesthesia. Serum cortisol and glucose concentrations were measured before, during, and after anesthesia. Urine specific gravity and volume were measured during anesthesia. Unassisted anesthetic recoveries were recorded by a digital video camera for later evaluation by 2 observers who were blinded to treatment. Results—Serum cortisol concentration was lower and serum glucose concentration was higher with MCRI treatment, compared with xylazine treatment. Time to sternal recumbency was longer with MCRI treatment, but no difference was seen between treatments for times to extubation, first movement, or standing. Objective (mean attempt interval) and subjective (visual analog score) recovery scores were significantly better with MCRI treatment, compared with xylazine treatment. Conclusions and Clinical Relevance—In isoflurane-anesthetized horses, premedication and administration of medetomidine as a constant rate infusion resulted in decreased serum cortisol concentration, increased serum glucose concentration, and superior anesthetic recovery characteristics, compared with conventional treatment with xylazine.

Continuous positive airway pressure (CPAP) decreases pulmonary shunt in anaesthetized horses

“…; Creighton et al. ). The additional use of a colloid after 2 hours of anaesthesia was based on personal experience in which long periods of anaesthesia showed substantial drops in CVP using this specific protocol.…”

“…We therefore conclude that CPAP has no clinically relevant effect on _ DO 2 and CO. The fluid regime used in our study was based on an expected high urinary output attributable to the use of a medetomidine CRI (Bettschart-Wolfensberger et al 2005;Creighton et al 2012). The additional use of a colloid after 2 hours of anaesthesia was based on personal experience in which long periods of anaesthesia showed substantial drops in CVP using this specific protocol.…”

Pharmacokinetics of ketamine and three metabolites in Beagle dogs under sevoflurane vs. medetomidine comedication assessed by enantioselective capillary electrophoresis

“…One possibility is the increased formation of hydroxyketamine metabolites, another is the increased elimination of unmodified ketamine through the kidneys. The α 2 -receptor agonist medetomidine causes the inhibition of the release of vasopressin and the increase of the excreted urine volume [38]. Furthermore, hyperglycemia mediated contemporaneously through the α 2 -receptor in the β-cells in the endocrine pancreas results in polyuria [39].…”

Effects of Medetomidine Constant Rate Infusion on Sevoflurane Requirement, Cardiopulmonary Function, and Recovery Quality in Thoroughbred Racehorses Undergoing Arthroscopic Surgery

“…In the previous comparison study of 1.7% of isoflurane versus 1.4% of isoflurane with medetomidine CRI, administration of medetomidine as CRI preserved more brisk eye reflexes when horses were maintained at 20%-30% lower inhalant anesthetic concentration, although the horses were at a similar plane of anesthesia during both treatments [13,20]. Traditionally, the depth of anesthesia in horses has been evaluated on the basis of ocular signs, such as spontaneous palpebral reflex and nystagmus.…”