EC50 of Remifentanil to Prevent Propofol Injection Pain

Background: Various strategies have been studied to reduce the propofol injection pain. This study was designed to find out effect-site target concentration (Ce) of remifentanil at which there was a 50% probability of preventing the propofol injection pain (EC50). Methods: Anesthesia was induced with a remifentanil TCI (Minto model). The Ce of remifentanil for the first patient started from 2.0 ng/ml. The Ce of remifentanil for each subsequent patient was determined by the response of the previous patient by Dixon up-and-down method with the interval of 0.5 ng/ml. After the remifentanil reached target concentrations, propofol was administered via a target-controlled infusion system based on a Marsh pharmacokinetic model using a TCI device (Orchestra$^{(R)}$; Fresenius-Vial, Brezins, France). The dose of propofol was effect site target-controlled infusion (TCI) of $3{\mu}g/ml$. Results: The EC50 of remifentanil to prevent the propofol injection pain was $1.80{\pm}0.35ng/ml$ by Dixon's up and down method. Conclusions: The EC50 of remifentanil to blunt the pain responses to propofol injection was $1.80{\pm}0.35ng/ml$ for propofol TCI anesthesia.