Effect of mepivacaine in an infraorbital nerve block on minimum alveolar concentration of isoflurane in clinically normal anesthetized dogs undergoing a modified form of dental dolorimetry

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Abstract
Objective—To evaluate the effects of a routinely used infraorbital nerve block, performed for dental procedures, on the anesthetic requirement for isoflurane in dogs. Design—Prospective controlled study. Animals—8 healthy adult Beagles. Procedures—Dogs were anesthetized with isoflurane, and the minimum alveolar concentration (MAC) of isoflurane was established. A modification of a well-established method of stimulating the dental pulp, dental dolorimetry, was used to deliver a noxious stimulus (electrical stimulation) for isoflurane MAC determination. Once the isoflurane MAC was established, an infraorbital nerve block was performed with mepivacaine. The isoflurane MAC was then determined with the addition of the nerve block. Measurements of heart rate and mean arterial blood pressure were obtained at specified time points (baseline and prevention and elicitation of purposeful movement) during the determination of MAC and in response to the noxious stimulus. Results—The mean ± SD isoflurane MAC without an infraorbital nerve block was 1.12 ± 0.13%. Isoflurane MAC with the regional mepivacaine anesthesia was 0.86 ± 0.11%. A significant reduction in isoflurane MAC (23%) was seen after the infraorbital nerve block, compared with results before the nerve block. With the exception of baseline measurements, no significant differences were found between treatments (isoflurane alone vs isoflurane with regional mepivacaine anesthesia) in heart rate or mean arterial blood pressure before or after the noxious stimulus. Conclusions and Clinical Relevance—The significant reduction in MAC of isoflurane supported the practice of the addition of regional anesthesia for painful dental procedures to reduce the dose-dependent cardiorespiratory effects of general anesthesia.

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