title: Minimum end-tidal sevoflurane concentration necessary to prevent movement during a constant rate infusion of morphine, or morphine plus dexmedetomidine in ponies.
abstract: OBJECTIVE
  To compare the effects of a constant rate infusion (CRI) of dexmedetomidine and morphine to those of morphine alone on the minimum end-tidal sevoflurane concentration necessary to prevent movement (MACNM ) in ponies.
  
  
  METHODS
  Prospective, randomized, crossover, 'blinded', experimental study.
  
  
  METHODS
  Five healthy adult gelding ponies were anaesthetized twice with a 3-week washout period.
  
  
  METHODS
  After induction of anaesthesia with sevoflurane in oxygen (via nasotracheal tube), the ponies were positioned on a surgical table (T0), and anaesthesia was maintained with sevoflurane (Fe'SEVO 2.5%) in 55% oxygen. Monitoring included pulse oximetry, electrocardiography and measurement of anaesthetic gases, arterial blood pressure and body temperature. The ponies were mechanically ventilated and randomly allocated to receive IV treatment M [morphine 0.15 mg kg⁻¹ (T10-T15) followed by a CRI (0.1 mg kg⁻¹ hour⁻¹)] or treatment DM [dexmedetomidine 3.5 μg kg⁻¹ plus morphine 0.15 mg kg⁻¹ (T10-T15) followed by a CRI of dexmedetomidine 1.75 μg kg⁻¹ hour⁻¹ and morphine 0.1 mg kg⁻¹ hour⁻¹]. At T60, a stepwise MACNM determination was initiated using constant current electrical stimuli at the skin of the lateral pastern region. Triplicate MACNM estimations were obtained and then averaged in each pony. Wilcoxon signed-rank test was used to detect differences in MAC between treatments (α = 0.05).
  
  
  RESULTS
  Sevoflurane-morphine MACNM values (median (range) and mean ± SD) were 2.56 (2.01-4.07) and 2.79 ± 0.73%. The addition of a continuous infusion of dexmedetomidine significantly reduced sevoflurane MACNM values to 0.89 (0.62-1.05) and 0.89 ± 0.22% (mean MACNM reduction 67 ± 11%).
  
  
  CONCLUSIONS
  Co-administration of dexmedetomidine and morphine CRIs significantly reduced the MACNM of sevoflurane compared with a CRI of morphine alone at the reported doses.
authors.affiliation: Department of Surgery and Anaesthesia of Domestic Animals, Faculty of Veterinary Medicine, University of Ghent, Merelbeke, Belgium.
authors.forename: Miguel
authors.initials: M
authors.lastname: Gozalo-Marcilla
authors.forename: Klaus
authors.initials: K
authors.lastname: Hopster
authors.forename: Frank
authors.initials: F
authors.lastname: Gasthuys
authors.forename: Anna Elisabeth
authors.initials: AE
authors.lastname: Krajewski
authors.forename: Andrea
authors.initials: A
authors.lastname: Schwarz
authors.forename: Stijn
authors.initials: S
authors.lastname: Schauvliege
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D000818:Animals; D020927:Dexmedetomidine / Q000008:administration & dosage / Q000494:pharmacology*; D004334:Drug Administration Schedule; D004359:Drug Therapy, Combination; D006736:Horses; D006993:Hypnotics and Sedatives / Q000008:administration & dosage / Q000494:pharmacology; D007275:Injections, Intravenous; D008738:Methyl Ethers / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology*; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D000077149:Sevoflurane
chemical_list: D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D006993:Hypnotics and Sedatives; D008738:Methyl Ethers; D000077149:Sevoflurane; D020927:Dexmedetomidine; D009020:Morphine
keywords: constant-rate infusion; dexmedetomidine; minimal alveolar concentration; morphine; ponies; sevoflurane