Median effective target plasma concentration of remifentanil inhibiting responses to skull-pin placement when combined with propofol in female patients undergoing neurosurgery

Objective To determine the median effective target plasma concentration (EC50) of remifentanil inhibiting responses to skull-pin placement when combined with propofol in the female patients undergoing neurosurgery. Methods Sixteen female patients, aged 20-60 yr, with body mass index of 18-30 kg/m2, of American Society of Anesthesiologists physical status Ⅰor Ⅱ, scheduled for elective neurosurgery under general anesthesia, were enrolled in this study.Anesthesia was induced with propofol and remifentanil given by target-controlled infusion and iv rocuronium 0.6 mg/kg.The target plasma concentration (Cp) of remifentanil and propofol was set at 5 ng/ml and 3 μg/ml, respectively.At 3 min after tracheal intubation, the target Cp of remifentanil was adjusted and set at 5 ng/ml in the first patient.The skull-pin was placed after the target effect-site and plasma concentrations were balanced.The Cp increased/decreased by 20% each time in the next patient depending on whether or not the response to skull-pin placement was positive.The ratio between the two successive concentrations was 1.2.The response to skull-pin placement was defined as positive when heart rate and/or mean arterial pressure increased by 20% of the baseline value within 1 min after placement.The EC50 and 95% confidence interval of remifentanil required to inhibit responses to skull-pin placement were calculated when combined with propofol. Results The EC50 (95% confidence interval) of remifentanil required to inhibit responses to skull-pin placement was 3.74 (3.43-4.09) ng/ml when combined with propofol. Conclusion When combined with propofol, the EC50 of remifentanil inhibiting responses to skull-pin placement is 3.74 ng/ml in the female patients undergoing neurosurgery. Key words: Piperidines; Propofol; Female; skull-pin; Dose-response relationship, drug; Drug delivery systems