Changes in the minimum alveolar concentration of isoflurane and some cardiopulmonary measurements during three continuous infusion rates of dexmedetomidine in dogs.
OBJECTIVE
To measure the change in the minimum alveolar concentration of isoflurane associated with three constant rate infusions of dexmedetomidine.


METHODS
Prospective, randomized, and blinded experimental trial. Animals Six healthy 6-year-old Beagles weighing between 13.0 and 17.7 kg.


METHODS
The dogs received each of four treatments; saline or dexmedetomidine at 0.1, 0.5 or 3 microg kg(-1) loading dose given intravenously (IV) over 6 minutes followed by infusions at 0.1, 0.5 or 3 microg kg(-1) hour(-1), respectively. There were 2 weeks between treatments. The dogs were mask-induced with and maintained on isoflurane in oxygen. Acetated Ringer's (5 mL kg(-1) hour(-1)) and saline or dexmedetomidine (each at 0.5 mL kg(-1) hour(-1)) were given IV. Pulse rate, blood pressure, samples for the measurement of blood gases, pH, lactate, packed cell volume (PCV), total protein (TP) and dexmedetomidine concentrations were obtained from an arterial catheter. Sixty minutes after induction minimum alveolar concentration (MAC) was determined by intermittently applying supramaximal electrical stimuli to the thoracic and pelvic limbs. Cardiopulmonary measurements and arterial blood samples were collected before each set of stimuli. Statistical analyses were conducted with analysis of variance or mixed models according to the experimental design.


RESULTS
There was a significant decrease in the MAC of isoflurane associated with 0.5 and 3 microg kg(-1) hour(-1) but not with 0.1 mg kg(-1)hour(-1). Serum concentrations of dexmedetomidine were not measurable at the 0.1 mg kg(-1) hour(-1) and averaged 0.198 +/- 0.081 and 1.903 +/-0.621 ng mL(-1) for the 0.5 and 3 microg kg(-1) hour(-1) infusion rates, respectively. Heart rate decreased with increasing doses of dexmedetomidine while blood pressure increased. Packed cell volume increased at 3 microg kg(-1) hour(-1) but not with other doses.


CONCLUSIONS
Dexmedetomidine infusions decrease the intra-operative requirement for isoflurane and may be useful in managing dogs undergoing surgery, where the provision of analgesia and limitation of the stress response is desirable.
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA, USA. pjpascoe@ucdavis.edu
Peter J
PJ
Pascoe
Marja
M
Raekallio
Erja
E
Kuusela
Brett
B
McKusick
Mikael
M
Granholm
D000758:Anesthesia / Q000662:veterinary; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics*; D000818:Animals; D001639:Bicarbonates / Q000097:blood; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000097:blood; D020927:Dexmedetomidine / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004347:Drug Interactions; D006339:Heart Rate / Q000187:drug effects; D006993:Hypnotics and Sedatives / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D007530:Isoflurane / Q000008:administration & dosage / Q000493:pharmacokinetics*; D019344:Lactic Acid / Q000097:blood; D010100:Oxygen / Q000097:blood; D012119:Respiration / Q000187:drug effects
D018685:Anesthetics, Inhalation; D001639:Bicarbonates; D006993:Hypnotics and Sedatives; D002245:Carbon Dioxide; D019344:Lactic Acid; D020927:Dexmedetomidine; D007530:Isoflurane; D010100:Oxygen