Effect of nitrous oxide on the minimum alveolar concentration for sevoflurane and the minimum alveolar concentration derivatives that prevent motor movement and autonomic responses in dogs

Abstract

Objective-To investigate the effects of the concurrent administration of 70% N 2O on the minimum alveolar concentration (MAC) for sevoflurane in dogs, the MAC derivative that blocks motor movement (MAC NM), and the MAC derivative that blocks autonomic responses (MAC BAR). 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, MAC NM, and MAC BAR 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, MAC NM, and MAC BAR were determined again. Percentage changes from the respective baseline concentrations for MAC, MAC NM, and MAC BAR were calculated after the administration of N 2O. Results-Baseline median values for the MAC, MAC NM, and MAC BAR for sevoflurane were 1.75%, 2.00%, and 2.50%, respectively. Addition of 70% N2O significantly decreased MAC, MAC NM, and MAC BAR 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% N 2O caused a clinically important and significant decrease in the MAC, MAC NM, and MAC BAR for sevoflurane in dogs.