This study was aimed to evaluate Bispectral index (BIS) variables in dogs anesthetized with continuous infusion of propofol associated or not to nitrous oxide.

Fourteen dogs, adult healthy mongrel dogs, males or females, were equally divided into two groups (G1 and G2). The G1 animals received propofol (10 mg/kg) intravenously to induce the general anesthesia. Immediately after, the dogs were intubated, and received oxygen (30%) with nitrous oxide (70%). Concomitantly, continuous infusion of propofol (0.6 mg/kg/min) was initiated using an infusion pump. The G2 animals were submitted to the same protocol, but the gas mixture was substituted to oxygen (100%). BIS values (maximum, minimum and mean), suppression rate (SR), sign of quality (SQI) and electromyography (EMG) were evaluated 30 minutes after the infusion beginning (M1), and at each 10 minutes, during 50 minutes (M2, M3, M4, M5, and M6, respectively). Statistical analyses of the data were performed using analysis of variance (ANOVA), followed by the Tukey test (p<0.05).

There were no differences between groups at the same time, and similarly did not denote differences occurring with the time within the same group.

The present results led us to conclude that nitrous oxide do not interfere in BIS values in dogs anesthetized with continuous infusion of propofol. Then, these new monitoring method could be used to improve the anesthetic management with these protocols.