Assessment of isoflurane-induced anesthesia in ferrets and rats

OBJECTIVE: To characterize isoflurane (ISO)-induced anesthesia in ferrets and rats. ANIMALS: 8 ferrets (Mustela putorius furo) and 8 Sprague-Dawley rats. PROCEDURE: Ferrets and rats were anesthetized in a similar manner, using ISO in oxygen. Minimum alveolar concentration (MAC) was determined, using the tail-clamp method. Immediately thereafter, assessments were recorded for 0.8, 1.0, 1.5, and 2.0 MAC (order randomized) of ISO. RESULTS: MAC of ISO was (mean +/- SEM) 1.74 +/- 0.03 and 1.58 +/- 0.05% for ferrets and rats, respectively. Mean arterial blood pressure (MAP) was 75.0 +/- 4.3 and 107.9 +/- 2.7 mm Hg at 0.8 MAC for ferrets and rats, respectively, and decreased in a parallel dose-dependent manner. Respiratory frequency decreased in rats as ISO dose increased; however, respiratory frequency increased in ferrets as ISO dose increased from 0.8 to 1.5 MAC but then decreased at 2.0 MAC. At 0.8 MAC, hypoventilation was much greater in ferrets (PaCO2 = 71.4 +/- 3.5 mm Hg), compared with rats (PaCO2 = 57.7 +/- 1.9 mm Hg). In both species, PaCO2 progressively increased as anesthetic dose increased. Eyelid aperture of ferrets increased in a dose-dependent manner. Pupil diameter in ferrets and rats increased as ISO dose increased. CONCLUSIONS AND CLINICAL RELEVANCE: The MAP and PaCO2 in ferrets and rats and eyelid aperture in ferrets consistently and predictably changed in response to changes in anesthetic dose of ISO. Magnitude of respiratory depression was greater in ferrets than rats. Changes in MAP and PaCO2 in ferrets and rats and eyelid aperture in ferrets are consistent guides to changes in depth of ISO-induced anesthesia.