Validation of several types of noxious stimuli for use in determining the minimum alveolar concentration for inhalation anesthetics in dogs and rabbits.

OBJECTIVE: To compare 3 types of noxious stimuli applied to various anatomic areas of anesthetized dogs and rabbits for determination of the minimum alveolar concentration (MAC). ANIMALS: 10 dogs and 10 rabbits. PROCEDURE: Dogs were anesthetized with isoflurane and halothane in a randomized order. Rabbits were anesthetized with isoflurane. The MAC was determined by skin incision on the lateral aspect of the chest; clamping of the tail, paw of the forelimb, and paw of the hind limb; and application of electrical current to the oral mucosa (dogs only), forelimb, and hind limb. The MAC was the end-tidal concentration midway between the value permitting and preventing purposeful movement in response to noxious stimuli.
RESULTS: In dogs, mean +/- SEM MAC for isoflurane was 1.27 +/- 0.05% for clamping stimuli, 1.36 +/- 0.04% for oral electrical stimulation, 1.35 +/- 0.04% for electrical stimulation to the limbs, and 1.01 +/- 0.07% for surgical incision. The MAC for halothane was 0.97 +/- 0.03% for tail clamping, 0.96 +/- 0.03% for clamping of the limbs, 1.04 +/- 0.03% for electrical stimulation, and 0.75 +/- 0.06% for surgical incision. In rabbits, MAC for isoflurane was 2.08 +/- 0.02% for clamping stimuli, 2.04 +/- 0.02% for electrical stimulation, and 0.90 +/- 0.02% for surgical incision. The MAC for surgical incision was significantly lower than values for the other methods in both species. CONCLUSIONS AND CLINICAL RELEVANCE: Use of electrical current and clamping techniques resulted in similar MAC values. Surgical incision underestimated MAC values in dogs and rabbits.