Purpose: Various strategies have been studied to reduce the discomfort of rocuronium injection. This study was designed to determine the effect-site target concentration (Ce) of remifentanil at which there was a 50% probability of preventing movement from pain in response to the injection of rocuronium (EC(50)).
Methods: Anesthesia was induced with a propofol target-controlled infusion (TCI, Marsh model) and remifentanil TCI (Minto model). Effect-site target concentration of propofol was 3 microg/ml. Ce of remifentanil for the first patient started at 2.0 ng/ml. Ce of remifentanil for each subsequent patient was determined by the response of the previous patient by the Dixon up-and-down method with an interval of 0.5 ng/ml. After both drugs reached target concentration, rocuronium 0.8 mg/kg was administered, and the pain response was observed.
Results: The EC(50) of remifentanil was 1.5 +/- 0.45 ng/ml by Dixon's up-and-down method. From probit analysis, the EC(50) of remifentanil was 1.37 ng/ml (95% confidence limits, 0.69-2.15 ng/ml), and the EC(95) was 3.19 ng/ml (95% confidence limits, 2.31-11.24 ng/ml).
Conclusion: The EC(50) of remifentanil to blunt the withdrawal responses to rocuronium injection was 1.37-1.5 ng/ml during 3 microg/ml propofol TCI anesthesia.