• Klaus Hopster, Christina Müller, Charlotte Hopster-Iversen, Jessica Stahl, Karl Rohn, and Sabine Kästner.
• Equine Clinic, University of Veterinary Medicine Hanover, Foundation, Hanover, Germany.
• Vet Anaesth Analg. 2014 Jan 1;41(1):25-35.

ObjectivesTo compare cardiovascular effects and recovery quality and duration of total intravenous anaesthesia (TIVA) with xylazine-ketamine-midazolam or dexmedetomidine-ketamine-midazolam.Study DesignProspective, randomized experimental cross-over trial.AnimalsEight adult warmblood horses.MethodsAfter sedation with acepromazine and either xylazine [0.5 mg kg(-1) , intravenously (IV)] or dexmedetomidine (3.5 μg kg(-1) IV) anaesthesia was induced with ketamine and midazolam and maintained with a constant rate infusion (CRI) of xylazine (1 mg kg(-1)  hour(-1) ) [XKM] or dexmedetomidine (7 μg kg(-1)  hour(-1) ) [DKM] in combination with midazolam (0.1 mg kg(-1)  hour(-1) ), and ketamine infusion (initially 3 mg kg(-1)  hour(-1) ) for 120 minutes. Ketamine infusion rate was increased in response to positive reactions to electrical nociceptive stimulation performed every 30 minutes. Heart rate (HR), mean arterial blood pressure (MAP) and cardiac output (Q˙t) were measured before treatment (baseline), after sedation (not Q˙t), and during anaesthesia. Xylazine, dexmedetomidine, midazolam and ketamine kinetics were calculated, from plasma drug concentrations. Twenty minutes after end of TIVA, flumazenil (0.01 mg kg(-1) IV) was administered. Recovery quality and duration were assessed. Two-way analysis of variance with repeated measurements or Wilcoxon signed rank test as relevant were used to analyse data with an alpha of 5%.ResultsCompared to baseline, MAP did not change, while similar, but limited, decreases in HR and Q˙t were observed in both TIVA's. Mean ketamine doses of 3.7 mg kg(-1)  hour(-1) were required with both treatments. Plasma concentrations of dexmedetomidine and xylazine showed high intra- and inter-individual changes with elimination half-lifes of 46 ± 7 minutes and 64 ± 13 minutes, respectively. Recovery quality was good to excellent with mean duration of 37 ± 16 and 46 ± 21 minutes after stopping TIVA with XKM and DKM, respectively.Conclusions And Clinical RelevanceBoth drug combinations are suitable to maintain anaesthesia for two hours, with good cardiovascular and good to excellent recovery conditions.© 2013 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.

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