• Rodney W Schnellbacher, James W Carpenter, Diane E Mason, Butch KuKanich, Hugues Beaufrère, and Courtney Boysen.
• Department of Clinical Science, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.
• Am. J. Vet. Res. 2013 Nov 1; 74 (11): 1377-84.

ObjectiveTo evaluate the effect of a continuous rate infusion (CRI) of lidocaine on the minimum alveolar concentration (MAC) of isoflurane in rabbits.AnimalsFive 12-month-old female New Zealand White rabbits (Oryctolagus cuniculus).ProceduresRabbits were anesthetized with isoflurane. Baseline isoflurane MAC was determined by use of the tail clamp technique. A loading dose of lidocaine (2.0 mg/kg, IV) was administered followed by a CRI of lidocaine at 50 μg/kg/min. After 30 minutes, isoflurane MAC was determined. Another loading dose was administered, and the lidocaine CRI then was increased to 100 μg/kg/min. After 30 minutes, isoflurane MAC was determined again. Plasma samples were obtained for lidocaine analysis after each MAC determination.ResultsBaseline isoflurane MAC was 2.09%, which was similar to previously reported values in this species. Lidocaine CRI at 50 and 100 μg/kg/min induced significant reductions in MAC. The 50 μg/kg/min CRI resulted in a mean plasma lidocaine concentration of 0.654 μg/mL and reduction of MAC by 10.5%. The 100 μg/kg/min CRI of lidocaine resulted in a mean plasma concentration of 1.578 μg/mL and reduction of MAC by 21.7%. Lidocaine also induced significant decreases in arterial blood pressure and heart rate. All cardiopulmonary variables were within reference ranges for rabbits anesthetized with inhalation anesthetics. No adverse effects were detected; all rabbits had an uncomplicated recovery from anesthesia.Conclusions And Clinical RelevanceLidocaine administered as a CRI at 50 and 100 μg/kg/min decreased isoflurane MAC in rabbits. The IV administration of lidocaine may be a useful adjunct in anesthesia of rabbits.

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