title: The effect of ketamine on the MACBAR of sevoflurane in dogs.
abstract: OBJECTIVE
  To determine the effect of intravenous ketamine on the minimum alveolar concentration of sevoflurane needed to block autonomic response (MAC(BAR)) to a noxious stimulus in dogs.
  
  
  METHODS
  Randomized, crossover, prospective design.
  
  
  METHODS
  Eight, healthy, adult male, mixed-breed dogs, weighing 11.2-16.1 kg.
  
  
  METHODS
  Dogs were anesthetized with sevoflurane on two occasions, 1 week apart, and baseline MAC(BAR) (B-MAC(BAR)) was determined on each occasion. MAC(BAR) was defined as the mean of the end-tidal sevoflurane concentrations that prevented and allowed an increase (≥15%) in heart rate or invasive mean arterial pressure in response to a noxious electrical stimulus (50 V, 50 Hz, 10 ms). Dogs then randomly received either a low-dose (LDS) or high-dose series (HDS) of ketamine, and treatment MAC(BAR) (T-MAC(BAR)) was determined. The LDS had an initial loading dose (LD) of 0.5 mg kg(-1) and constant rate infusion (CRI) at 6.25 μg kg(-1) minute(-1), followed, after T-MAC(BAR) determination, by a second LD (1 mg kg(-1)) and CRI (12.5 μg kg(-1) minute(-1)). The HDS had an initial LD (2 mg kg(-1)) and CRI (25 μg kg(-1) minute(-1)) followed by a second LD (3 mg kg(-1)) and CRI (50 μg kg(-1) minute(-1)). Data were analyzed with a mixed-model anova and are presented as LSM ± SEM.
  
  
  RESULTS
  The B-MAC(BAR) was not significantly different between treatments. Ketamine at 12.5, 25, and 50 μg kg(-1) minute(-1) decreased sevoflurane MAC(BAR), and the maximal decrease (22%) occurred at 12.5 μg kg(-1) minute(-1). The percentage change in MAC(BAR) was not correlated with either the log plasma ketamine or norketamine concentration.
  
  
  CONCLUSIONS
  Ketamine at clinically relevant doses of 12.5, 25, and 50 μg kg(-1) minute(-1) decreased sevoflurane MAC(BAR), although the reduction was neither dose-dependent nor linear.
authors.affiliation: Animal Emergency & Referral Associates, Fairfield, NJ, USA.
authors.forename: Lydia
authors.initials: L
authors.lastname: Love
authors.forename: Christine
authors.initials: C
authors.lastname: Egger
authors.forename: Barton
authors.initials: B
authors.lastname: Rohrbach
authors.forename: Sherry
authors.initials: S
authors.lastname: Cox
authors.forename: Meredith
authors.initials: M
authors.lastname: Hobbs
authors.forename: Thomas
authors.initials: T
authors.lastname: Doherty
mesh_terms: D000762:Anesthesia Recovery Period; D000769:Anesthesia, Inhalation / Q000662:veterinary*; D000771:Anesthesia, Intravenous / Q000662:veterinary*; D000778:Anesthetics, Dissociative / Q000097:blood / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001341:Autonomic Nervous System / Q000187:drug effects*; D001794:Blood Pressure / Q000187:drug effects; D018592:Cross-Over Studies; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D007649:Ketamine / Q000097:blood / Q000494:pharmacology*; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology*; D011446:Prospective Studies; D011650:Pulmonary Alveoli; D000077149:Sevoflurane
chemical_list: D000778:Anesthetics, Dissociative; D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007649:Ketamine