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ANESTHETIC PHARMACOLOGY

The Effects of Intravenous Lidocaine Administration on the Minimum Alveolar Concentration of Isoflurane in Cats

Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis

Address correspondence to Bruno Pypendop, DrMedVet, DrVetSci, Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA 95616. Address email to bhpypendop{at}ucdavis.edu

Lidocaine decreases the minimum alveolar concentration (MAC) of inhaled anesthetics and has been used clinically to reduce the requirements for other anesthetic drugs. In this study we examined the effects of lidocaine on isoflurane MAC in cats. Six cats were studied. In Experiment 1, the MAC of isoflurane was determined. An IV bolus of lidocaine 2 mg/kg was then administrated and venous plasma lidocaine concentrations were measured to determine pharmacokinetic values. In Experiment 2, lidocaine was administered to achieve target plasma concentrations between 1 and 11 µg/mL and the MAC of isoflurane was determined at each lidocaine plasma concentration. Actual lidocaine plasma concentrations were 1.06 ± 0.12, 2.83 ± 0.39, 4.93 ± 0.64, 6.86 ± 0.97, 8.86 ± 2.10, and 9.84 ± 1.34 µg/mL for the target concentrations of 1, 3, 5, 7, 9, and 11 µg/mL, respectively. The MAC of isoflurane in this study was 2.21% ± 0.17%, 2.14% ± 0.14%, 1.88% ± 0.18%, 1.66% ± 0.16%, 1.47% ± 0.13%, 1.33% ± 0.23%, and 1.06% ± 0.19% at lidocaine target plasma concentrations of 0, 1, 3, 5, 7, 9, and 11 µg/mL, respectively. Lidocaine, at target plasma concentrations of 1, 3, 5, 7, 9, and 11 µg/mL, linearly decreased isoflurane MAC by –6% to 6%, 7% to 28%, 19% to 35%, 28% to 45%, 29% to 53%, and 44% to 59%, respectively. We conclude that lidocaine decreases the MAC of isoflurane.

IMPLICATIONS: IV lidocaine decreased the minimum alveolar concentration of isoflurane in a linear and dose-dependent fashion in cats. These results suggest that IV lidocaine might be useful whenever decreasing the requirements for inhaled anesthetics is desirable.

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