Intravenous Administration of Ropivacaine Reduces Minimal Alveolar Concentration of Sevoflurane in Rats

Background: Whether intravenous infusion of ropivacaine at a constant rate can affect the minimum alveolar concentration (MAC) of sevoflurane in rats and different concentration can produce different effects. Methods: We used the Dixon “up-and-down” method to determine the MAC of sevoflurane in three groups (20 subjects per group). After a 30-minute equilibration, the medica-tions (saline, 0.5% ropivacaine or 1.0% ropivacaine) were continuously infused at a rate of 0.5 mL/h/kg for 30 minutes, and the response to the supramaximal noxious stimulus was recorded (movement versus no movement). Results: The MAC was 2.34 ± 0.26% (95% confidence interval [CI], 2.22-2.46) in the saline group, 1.22 ± 0.31% (95%CI, 1.07-1.37) in the 0.5% ropivacaine group, and 1.06 ± 0.42% (95%CI, 0.86-1.26) in the 1.0% ropivacaine group. The MAC of the 0.5% ropivacaine (mean difference of 1.12% sevoflurane [95% adjusted CI, 0.86-1.38]; P < 0.01) and 1.0% ropivacaine groups (mean difference of 1.28% sevoflurane [95% adjusted CI, 1.02-1.54]; P < 0.01) were significantly lower than that of the saline group. Conclusion: Intravenous administration of 0.5% and 1.0% ropivacaine both decreased the MAC of sevoflurane in rats, and 1.0% ropivacaine showed more decline. (Funded by the Distinguished Professorships Awards from the China Medical Board.) ABSTRACT