The effect of remifentanil infusion on sevoflurane minimum alveolar concentration-no movement (MACNM) and bispectral index in dogs

Objective To determine the effect of remifentanil infusion on the minimum alveolar concentration of sevoflurane preventing movement (SEVOMACNM) and bispectral index (BIS) in dogs.Study design Prospective, unmasked study.Animals A total of 10 adult Beagle dogs weighing 9.0 +/- 1.1 kg.Methods Dogs were anesthetized with sevoflurane and baseline SEVOMACNM was determined. Remifentanil was infused at 5, 10 and 20 mu g kg-1 hour-1, in sequence, with 20 minutes washout between infusions. Variables moni-tored throughout anesthesia included heart rate (HR), oscillometric blood pressure, end-tidal partial pressure of carbon dioxide, end-tidal sevoflurane concentration (FE0Sevo) and BIS. SEVOMACNM after remifentanil infusion (SEVOMACNM-REMI) determination started 20 minutes after the start of each infusion. Venous blood samples were collected for plasma remifentanil concentration determina-tion at baseline, SEVOMACNM-REMI determination time points, and 20 minutes after each infusion was stopped. A mixed model analysis was used to determine the effect of remifentanil infusion on response variables. The relation-ships between BIS and FE0Sevo, plasma remifentanil con-centrations and the percentage decrease in baseline SEVOMACNM were evaluated (p < 0.05).Results The overall SEVOMACNM at baseline was 2.47 +/- 0.11%. Addition of remifentanil at all infusion rates signif-icantly decreased SEVOMACNM, but the medium and high doses resulted in significantly greater decreases in SEVOMACNM than the lower dose. There was no difference in SEVOMACNM percentage change between infusions 10 and 20 mu g kg-1 hour-1. Plasma remifentanil concentra-tions were significantly different in all infusion rates. Base -line BIS value was 70 +/- 1 and was lower than the BIS values recorded during all remifentanil infusions. BIS values were not significantly different among infusion rates. HR was lower and mean arterial pressure was higher during remifentanil infusions than at baseline.Conclusions and clinical relevance All remifentanil in-fusions decreased SEVOMACNM in dogs. Remifentanil infu-sion at any rate studied did not reduce BIS values.

Automated summary

This study aimed to determine the effect of remifentanil infusion on the minimum alveolar concentration of sevoflurane preventing movement (SEVOMACNM) and bispectral index (BIS) in dogs. The results showed that remifentanil infusion significantly decreased SEVOMACNM, but had no effect on BIS.