Objective: To characterize the effect of α2-adrenoceptor antagonism on the minimum alveolar concentration of isoflurane (MACISO) in cats. Study design: Prospective experimental study. Animals: A group of five healthy adult male neutered cats. Methods: Cats were anesthetized with isoflurane in oxygen and instrumented. MACISO was determined in duplicate in five cats, before and during administration of atipamezole (250 μg kg−1 followed by 250 μg kg−1 hour−1) using the bracketing technique and tail clamping. Estimates of MACISO obtained before and during administration of atipamezole were compared using a two-tailed paired t test. Results: MACISO during atipamezole administration (mean ± standard deviation 2.73% ± 0.07%) was significantly larger than before atipamezole administration (1.95% ± 0.13%; p < 0.0001). Conclusion and clinical relevance: The role of α2-adrenoceptors in inhaled anesthetic-induced immobility may be larger than previously thought. Antagonism of an α2-adrenoceptor agonist during inhalation anesthesia may result in an increase in MAC disproportionate to the MAC reduction induced by the agonist.
- minimum alveolar concentration
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