The Interaction between Remifentanil and Propofol during Total Intravenous Anesthesia and the Adequate Effect Site Concentration

Kim, Won Ho; Ahn, Hyun Joo

Abstract

BACKGROUND: This study was performed to evaluate the interaction between remifentanil and propofol by comparing median-effect concentration (EC50) of single and co-administration, and to find adequate combination doses for general anesthesia for gastrectomy.
METHODS
Thirty-six ASA physical status 1 or 2 patients scheduled for gastrectomy were randomly assigned to the remifentanil, propofol, or combination group.To obtain the dose-effect curve of remifentanil or propofol only, the effect site concentration of each drug was escalated until bispectral index (BIS) was reached 40 by a target-controlled infusion (TCI) during the steady operational period.For the combination group, 0.25, 0.5, 1, 2, and 2.5 timed EC50 of each drug were co-administered.The heart rate, mean arterial pressure and BIS were measured during the study period.The interaction between remifentanil and propofol was analyzed with using isobologram.
RESULTS
The EC50 of remifentanil for hypnosis (BIS 40) was 1.96 ng/ml, and that of propofol was 1.35microgram/ml.In the combination group, the EC50 of remifentanil was 0.81 ng/ml and that of propofol was 0.56microgram/ml.EC90 of remifentanil and propofol alone were 13.43 ng/ml and 4.88microgram/ml. For EC90 of the combination group, remifentanil 3.54 ng/ml and propofol 2.50 microgram/ml were required.The distance from the theoretical additive line in the isobologram was larger in the higher doses (EC50 < EC75 < EC90).
CONCLUSIONS
This study shows that remifentanil and propofol reveal synergism by isobolographic analysis during intravenous anesthesia.