The cardiovascular status of isoflurane-anaesthetized horses with and without dexmedetomidine constant rate infusion evaluated at equivalent depths of anaesthesia.
OBJECTIVE
To compare cardiac index and oxygen extraction at equivalent depths of anaesthesia between isoflurane-anaesthetized horses and horses anesthetized with isoflurane and dexmedetomidine CRI.


METHODS
Sequential, blinded, randomized, balanced, crossover study.


METHODS
Eight horses weighing a mean ± standard deviation of 478 ± 58 kg.


METHODS
Horses were premedicated with 0.03 mg kg(-1) acepromazine intramuscularly (IM) and 8 μg kg(-1) dexmedetomidine intravenously (IV). Anaesthesia was induced with 2.5 mg kg(-1) ketamine and 0.1 mg kg(-1) midazolam IV and maintained with isoflurane in oxygen and air. Horses were mechanically ventilated. Fractional concentration of end-tidal isoflurane (Fe'Iso) was stabilized at 1.7% with a CRI of 0.9% NaCl (IsoNaCl), or at 1.1% with 1.75 μg kg(-1)  hour(-1) dexmedetomidine (IsoDex). Mean arterial blood pressure was maintained above 60 mmHg by dobutamine infusion. Following nociceptive electrical stimulation, Fe'Iso was stabilized at a 0.1% lower concentration and nociceptive stimulation was repeated. This procedure was continued until the horse moved. Fe'Iso values prior to the concentration at which movement occurred were considered to indicate equivalent depths of anaesthesia between treatments. Cardiac index and oxygen extraction were compared at equivalent depths of anaesthesia using a paired Student's t-test.


RESULTS
Cardiac index differed between IsoNaCl at 61 ± 12 mL kg(-1)  minute(-1) and IsoDex at 48 ± 10 mL kg(-1)  minute(-1) (p = 0.047). In addition, oxygen extraction differed between IsoNaCl at 3.4 ± 0.8 mL kg(-1)  minute(-1) and IsoDex at 4.5 ± 0.5 mL kg(-1)  minute(-1) (p = 0.0042). Two horses receiving IsoNaCl were administered dobutamine at equivalent depths of anaesthesia (7.0 and 28.8 μg kg(-1)  hour(-1) , respectively).


CONCLUSIONS
Cardiovascular function in horses receiving isoflurane and 1.75 μg kg(-1)  minute(-1) dexmedetomidine is more compromised than in horses receiving a higher concentration of isoflurane and 0.9% NaCl CRI.
Department of Companion Animal Clinical Sciences, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway.
Åse I
ÅI
Risberg
Department of Food Safety and Infection Biology, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway.
Birgit
B
Ranheim
Centre for Epidemiology and Biostatistics, Faculty of Veterinary Medicine and Life Sciences, Norwegian University of Life Sciences, Oslo, Norway.
Randi I
RI
Krontveit
Department of Companion Animal Clinical Sciences, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway.
Andreas
A
Lervik
Department of Companion Animal Clinical Sciences, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway.
Henning A
HA
Haga
D000075:Acepromazine / Q000008:administration & dosage; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage*; D000758:Anesthesia / Q000379:methods / Q000662:veterinary*; D000762:Anesthesia Recovery Period; D018685:Anesthetics, Inhalation; D000818:Animals; D062186:Arterial Pressure / Q000187:drug effects; D002320:Cardiovascular Physiological Phenomena / Q000187:drug effects; D002319:Cardiovascular System / Q000187:drug effects*; D018592:Cross-Over Studies; D020927:Dexmedetomidine / Q000008:administration & dosage*; D018492:Dopamine Antagonists / Q000008:administration & dosage; D006736:Horses; D007530:Isoflurane; D007649:Ketamine; D008874:Midazolam; D010147:Pain Measurement / Q000379:methods / Q000662:veterinary; D011229:Preanesthetic Medication / Q000662:veterinary
D018712:Analgesics, Non-Narcotic; D018685:Anesthetics, Inhalation; D018492:Dopamine Antagonists; D000075:Acepromazine; D020927:Dexmedetomidine; D007649:Ketamine; D007530:Isoflurane; D008874:Midazolam
anaesthesia; dexmedetomidine; horse; isoflurane