Effects of tramadol on the minimum alveolar concentration of sevoflurane in dogs

To evaluate the effect of tramadol on sevoflurane minimum alveolar concentration (MACSEVO) in dogs. It was hypothesized that tramadol would dose-dependently decrease MACSEVO. Randomized crossover experimental study. Six healthy, adult female mixed-breed dogs (24.2 ± 2.6 kg). Each dog was studied on two occasions with a 7-day washout period. Anesthesia was induced using sevoflurane delivered via a mask. Baseline MAC (MACB) was determined starting 45 minutes after tracheal intubation. A noxious stimulus (50 V, 50 Hz, 10 ms) was applied subcutaneously over the mid-humeral area. If purposeful movement occurred, the end-tidal sevoflurane was increased by 0.1%; otherwise, it was decreased by 0.1%, and the stimulus was re-applied after a 20-minute equilibration. After MACB determination, dogs randomly received a tramadol loading dose of either 1.5 mg kg−1 followed by a continuous rate infusion (CRI) of 1.3 mg kg−1 hour−1 (T1) or 3 mg kg−1 followed by a 2.6 mg kg−1 hour−1 CRI (T2). Post-treatment MAC determination (MACT) began 45 minutes after starting the CRI. Data were analyzed using a mixed model anova to determine the effect of treatment on percentage change in baseline MACSEVO (p < 0.05). The MACB values were 1.80 ± 0.3 and 1.75 ± 0.2 for T1 and T2, respectively, and did not differ significantly. MACT decreased by 26 ± 8% for T1 and 36 ± 12% for T2. However, there was no statistically significant difference in the decrease between the two treatments. Tramadol significantly reduced MACSEVO but this was not dose dependent at the doses studied.