Effects of intravenous administration of lidocaine on the minimum alveolar concentration of sevofurane in horses

Objective-To determine effects of a continuous rate infusion of lidocaine on the minimum alveolar concentration (MAC) of sevofurane in horses. Animals-8 healthy adult horses. Procedures-Horses were anesthetized via IV administration of xylazine, ketamine, and di-azepam; anesthesia was maintained with sevofurane in oxygen. Approximately 1 hour after induction, sevofurane MAC determination was initiated via standard techniques. Following sevofurane MAC determination, lidocaine was administered as a bolus (1.3 mg/kg, IV, over 15 minutes), followed by constant rate infusion at 50 μg/kg/min. Determination of MAC for the lidocaine-sevofurane combination was started 30 minutes after lidocaine infusion was initiated. Arterial blood samples were collected after the lidocaine bolus, at 30-minute intervals, and at the end of the infusion for measurement of plasma lidocaine concentrations. Results-IV administration of lidocaine decreased mean ± SD sevofurane MAC from 2.42 ± 0.24% to 1.78 ± 0.38% (mean MAC reduction, 26.7 ± 12%). Plasma lidocaine concentrations were 2,589 ± 811 ng/mL at the end of the bolus; 2,065 ± 441 ng/mL, 2,243 ± 699 ng/ mL, 2,168 ± 339 ng/mL, and 2,254 ± 215 ng/mL at 30, 60, 90, and 120 minutes of infusion, respectively; and 2,206 ± 329 ng/mL at the end of the infusion. Plasma concentrations did not differ significantly among time points. Conclusions and Clinical Relevance-Lidocaine could be useful for providing a more balanced anesthetic technique in horses. A detailed cardiovascular study on the effects of IV infusion of lidocaine during anesthesia with sevofurane is required before this combination can be recommended.