EC50 of remifentanil to prevent pain during injection of microemulsion propofol

ABSTRACT

BACKGROUND: Microemulsion propofol that is free from lipid has been recently developed. However, it produces injection pain which is even greater than that of lipid emulsion propofol. Remifentanil has been used to reduce injection pain of propfol. So we evaluated half maximal effective concentration (EC50) of remifentanil to prevent pain during an administration of microemulsion propofol. METHODS: Remifentanil was infused to reach target effect-site concentration (Ce) before microemulsion propofol administration of target plasma-site concentration 5.0 microg/ml. Ce of remifentanil for the first patient was 4 ng/ml. Ce of remifentanil for each subsequent patient was determined by the response of the previous patient by the Dixon's up-and-down method with an interval of 0.2 ng/ml. After remifentanil reached target concentration, microemulsion propofol was administered, and the pain response was observed. Estimated EC50 and EC95 of remifentanil were calculated by probit analysis. RESULTS: Predicted EC50 of remifentanil by using Dixon's up-and- down method was 5.18 +/- 0.19 ng/ml. EC50 of remifentanil was 5.16 ng/ml (95% confidence intervals, 4.98-5.41 ng/ml) and EC95 was 5.47 ng/ml (95% confidence intervals, 5.29-7.0 ng/ml) by probit analysis. CONCLUSIONS: The EC50 of remifentanil to prevent injection pain of microemulsion propofol was 5.16-5.18 ng/ml.