title: The effect of dobutamine and bolus crystalloid fluids on the cardiovascular function of isoflurane-anaesthetised horses.
abstract: BACKGROUND
  Cardiac output does not always increase with dobutamine administration in anaesthetised horses and information on peripheral perfusion is lacking.
  
  
  OBJECTIVE
  To determine the effect of intravenous (i.v.) dobutamine infusion with and without a concurrent 20 mL/kg bodyweight (bwt) bolus of crystalloid fluids on the cardiovascular function of acepromazine premedicated, hypotensive, isoflurane-anaesthetised horses.
  
  
  METHODS
  Randomised, cross-over experiment.
  
  
  METHODS
  A total of 6 horses aged 5-13 years, weighing 464-578 kg were premedicated with acepromazine 0.02 mg/kg bwt and then sedated with xylazine 0.8 mg/kg bwt i.v. Anaesthesia was induced with ketamine 2.2 mg/kg bwt and diazepam 0.08 mg/kg bwt i.v. and maintained with isoflurane, adjusted to achieve a target mean arterial pressure (MAP) (60 mmHg ± 5%) 60 min post-induction of anaesthesia (T0). One of 2 treatments was then given. In treatment D, dobutamine was initially infused at 0.5 μg/kg bwt/min and adjusted to achieve a target MAP (80 mmHg ± 5%) within 30 min of infusion initiation. In treatment D+F dobutamine was administered as described for treatment D, with 20 mL/kg bwt Hartmann's solution infused i.v. over 20 min. Cardiac index (CI), haemoglobin concentration ([Hb]), arterial oxygen content (CaO2), oxygen delivery index (DO2I) and bilateral femoral arterial blood flow (FBF) were recorded at T0, 30 min following dobutamine initiation (T1) and 15 min following dobutamine cessation (T2). Data were analysed using a mixed-effect linear model (P<0.05 considered significant).
  
  
  RESULTS
  A significant increase in DO2I (P = 0.008, T0/T1), CaO2(P = 0.0002, T0/T1) and [Hb] (P<0.0001, T0/T1) and in CaO2(P = 0.0005, T1/T2) and [Hb] (P = 0.002,T1/T2) occurred during treatment D. A significant increase in FBF (P = 0.005, upper limb; P = 0.042 lower limb, T0/T1) occurred during treatment D+F. Significant differences between treatments were recorded at T1 ([Hb] P = 0.0001, CaO2P = 0.0003) and T2 ([Hb] P = 0.013). There was no change in CI during either treatment.
  
  
  CONCLUSIONS
  The increase in FBF seen with co-administration of fluids and dobutamine may provide a beneficial effect on muscle compared with the use of dobutamine alone.
authors.affiliation: College of Veterinary Medicine, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia.
authors.forename: C M
authors.initials: CM
authors.lastname: Loughran
authors.affiliation: College of Veterinary Medicine, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia.
authors.forename: A L
authors.initials: AL
authors.lastname: Raisis
authors.affiliation: College of Veterinary Medicine, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Hosgood
authors.affiliation: College of Veterinary Medicine, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia.
authors.forename: C J
authors.initials: CJ
authors.lastname: Secombe
authors.affiliation: College of Veterinary Medicine, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia.
authors.forename: G D
authors.initials: GD
authors.lastname: Lester
mesh_terms: D000769:Anesthesia, Inhalation / Q000662:veterinary; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002316:Cardiotonic Agents / Q000008:administration & dosage / Q000494:pharmacology; D018592:Cross-Over Studies; D000077324:Crystalloid Solutions; D004280:Dobutamine / Q000008:administration & dosage / Q000494:pharmacology*; D006736:Horses / Q000502:physiology*; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D007552:Isotonic Solutions / Q000008:administration & dosage / Q000494:pharmacology*; D010100:Oxygen / Q000097:blood; D015532:Rehydration Solutions / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D018685:Anesthetics, Inhalation; D002316:Cardiotonic Agents; D000077324:Crystalloid Solutions; D007552:Isotonic Solutions; D015532:Rehydration Solutions; D004280:Dobutamine; D007530:Isoflurane; D010100:Oxygen
keywords: anaesthesia; horse; hypotension; inotrope; vasoactive agent