title: Effects of a constant-rate infusion of dexmedetomidine on the minimal alveolar concentration of sevoflurane in ponies.
abstract: BACKGROUND
  Dexmedetomidine has been administered in the equine as a constant-rate infusion (CRI) during inhalation anaesthesia, preserving optimal cardiopulmonary function with calm and coordinated recoveries. Inhalant anaesthetic sparing effects have been demonstrated in other species, but not in horses.
  
  
  OBJECTIVE
  To determine the effects of a CRI of dexmedetomidine on the minimal alveolar concentration (MAC) of sevoflurane in ponies.
  
  
  METHODS
  Six healthy adult ponies were involved in this prospective, randomised, crossover, blinded, experimental study. Each pony was anaesthetised twice (3 weeks washout period). After induction with sevoflurane in oxygen (via nasotracheal tube), the ponies were positioned on a surgical table (T0), and anaesthesia was maintained with sevoflurane (expired sevoflurane fraction 2.5%) in 55% oxygen. The ponies were randomly allocated to treatment D (dexmedetomidine 3.5 µg/kg bwt i.v. [T10-T15] followed by a CRI of dexmedetomidine at 1.75 µg/kg bwt/h) or treatment S (bolus and CRI of saline at the same volume and rate as treatment D). After T60, MAC determination, using a classic bracketing technique, was initiated. Stimuli consisted of constant-current electrical stimuli at the skin of the lateral pastern region. Triplicate MAC estimations were obtained and averaged in each pony. Monitoring included pulse oximetry, electrocardiography, anaesthetic gas monitoring, arterial blood pressure measurement and arterial blood gases. Normocapnia was maintained by mechanical ventilation. Analysis of variance (treatment and period as fixed factors) was used to detect differences between treatments (α= 0.05).
  
  
  RESULTS
  An intravenous (i.v.) dexmedetomidine CRI decreased mean ± s.d. sevoflurane MAC from 2.42 ± 0.55 to 1.07 ± 0.21% (mean MAC reduction 53 ± 15%).
  
  
  CONCLUSIONS
  A dexmedetomidine CRI at the reported dose significantly reduces the MAC of sevoflurane.
authors.affiliation: Department of Surgery and Anaesthesia of Domestic Animals, Faculty of Veterinary Medicine, University of Ghent, Merelbeke, Belgium. miguel.gozalomarcilla@ugent.be
authors.forename: M
authors.initials: M
authors.lastname: Gozalo-Marcilla
authors.forename: K
authors.initials: K
authors.lastname: Hopster
authors.forename: F
authors.initials: F
authors.lastname: Gasthuys
authors.forename: L
authors.initials: L
authors.lastname: Hatz
authors.forename: A E
authors.initials: AE
authors.lastname: Krajewski
authors.forename: S
authors.initials: S
authors.lastname: Schauvliege
mesh_terms: D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000493:pharmacokinetics*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics*; D000818:Animals; D020927:Dexmedetomidine / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004334:Drug Administration Schedule; D004347:Drug Interactions; D005260:Female; D006736:Horses; D007275:Injections, Intravenous; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage / Q000493:pharmacokinetics*; D011650:Pulmonary Alveoli; D000077149:Sevoflurane
chemical_list: D018712:Analgesics, Non-Narcotic; D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D020927:Dexmedetomidine