Objective—To investigate the effects of the concurrent administration of 70% N2O on the minimum alveolar concentration (MAC) for sevoflurane in dogs, the MAC derivative that blocks motor movement (MACNM), and the MAC derivative that blocks autonomic responses (MACBAR).
Animals—7 adult sexually intact male mixed-breed dogs.
Procedures—For each dog, anesthesia was induced with sevoflurane delivered via a face mask. Initially, the baseline MAC, MACNM, and MACBAR for sevoflurane were determined by use of a noxious stimulus (50 V, 50 Hz, and 10 milliseconds) applied subcutaneously over a midulnar region. Nitrous oxide (70%) was added to the breathing circuit, and MAC, MACNM, and MACBAR were determined again. Percentage changes from the respective baseline concentrations for MAC, MACNM’ and MACBAR were calculated after the administration of N2O.
Results—Baseline median values for the MAC, MACNM, and MACBAR for sevoflurane were 1.75%, 2.00%, and 2.50%, respectively. Addition of 70% N2O significantly decreased MAC, MACNM, and MACBAR by 24.4%, 25.0%, and 35.2%, respectively, and these values did not differ significantly from each other.
Conclusions and Clinical Relevance—Supplementation with 70% N2O caused a clinically important and significant decrease in the MAC, MACNM’ and MACBAR for sevoflurane in dogs.