Objective: To characterize the effects of dexmedetomidine, with or without vatinoxan, on the minimum alveolar concentration of isoflurane (MAC ISO ) in cats. Study design: Randomized crossover experimental study. Animals: A group of six adult healthy male neutered cats. Methods: Cats were anesthetized with isoflurane in oxygen and instrumented. Dexmedetomidine was administered using a target-controlled infusion system to achieve 10 target plasma concentrations ranging from 0 to 40 ng mL –1 . Additionally, vatinoxan or an equivalent volume of saline was administered using a target-controlled infusion system to achieve a target plasma concentration of 4 μg mL –1 . Pulse rate (PR), respiratory rate, systolic arterial pressure (SAP), hemoglobin oxygen saturation, body temperature, end-tidal partial pressure of carbon dioxide and drug concentrations were measured. MAC ISO was determined at each target plasma dexmedetomidine concentration using the bracketing method and the tail clamp technique. Pharmacodynamic models were fitted to the plasma dexmedetomidine concentration-MAC ISO . Pharmacodynamic parameters were tested for equivalence, and if rejected, for difference. Results: Dexmedetomidine alone decreased MAC ISO in a plasma concentration-dependent manner. Maximum reduction was 77 ± 4%; the dexmedetomidine concentration producing 50% of the maximum decrease (IC 50 ) was 0.77 ng mL –1 . Vatinoxan increased MAC ISO in the absence of dexmedetomidine, decreased the potency of dexmedetomidine for its MAC ISO -reducing effect (IC 50 = 12 ng mL –1 ) and lessened the maximum MAC ISO reduction (60 ± 14%). PR decreased less and SAP increased less when dexmedetomidine was administered with vatinoxan compared with saline. Conclusion and clinical relevance: Vatinoxan altered the effect of dexmedetomidine on MAC ISO . A high plasma dexmedetomidine concentration in the presence of vatinoxan resulted in a large decrease in MAC ISO , with attenuation of dexmedetomidine-induced cardiovascular effects. The vatinoxan–dexmedetomidine combination may provide clinical benefits in isoflurane-anesthetized cats.
- minimum alveolar concentration
- α -agonist
- α -antagonist
ASJC Scopus subject areas