The Optimal Effect-site Concentration Of Remifentanil To Attenuate The Pain Caused By Propofol

Objective:To determine the optimal effect-site concentration of remifentanil for minimizing injection pain during induction with propofol. And complications ralated to remifentanil were assessed.Methods:Thirty ASA I-II patients, aged18-65years old, body mass index between18to25kg/m2, undergoing elective gynecological operation under general anesthesia were enrolled in this study. After entering the operating room, each patient was inserted with an18gauge venous cannula at his opisthenar. TCI pumps were used for plasma TCI of propofol and remifentanil. Marsh model was adopted for propofol while Minto model adopted for remifentanil. The target effect-site concentration (EC) of remifentanil for the first patient was set at3.0ng/ml. During remifentanil injection, remifentanil related complications were assessed by repeated observation and verbal questions until requilibrium between the plasma and effect-site concentration of remifentanil. As observed and recorded, the patient’s complications included the followings:hypotension (>20%decreased compared with baseline value), bradycardia (heart rate<50beats/min), chest wall rigidity (expressed as chest tightness and difficulty in breathing), desaturation (SpO2<95%), dizziness, nausea, cough, pruritus, and erythema. When the intended target EC of remifentanil was reached, TCI of propofol was started at a target EC of3.5μg/ml. During infusion of propofol, we repeatedly asked the patient’s feelings, observed their expressions and their body movements as well as recorded the level of pain(no pain, mild pain, moderate pain, severe pain). The infusions of propofol and remifentanil were continued until requilibrium between the plasma and effect-site concentration of propofol. Vecuronium0.1mg/kg and midazolan0.05mg/ml were given to facilitate tracheal intubation. The target EC of remifentanil was determined by the response of the previous patient using the midified Dixon’s up-and-down method. Then the bolus dose of remifentanil were increased/decreased by0.5ng/ml respectively each time.The values of HR, SBP, DBP and MAP(baseline, after taget EC of remifentanil was reached, after taget EC of propofol was reached) were record.Results:The EC of remifentanil in50%and95%of population (EC50and EC95) for minimizing injection pain of propofol were2.79ng/ml (95%confidence limits[CI] was2.33-3.16ng/ml) and3.69ng/ml (95%CI was3.27-6.30ng/ml) respectively. Significant hemodynamic fluctuations or severe respiratory complications was not found during remifentanil infusion.Conclusions:The optimal effect-site concentration of remifentanil for minimizing injection pain during induction with propofol was3.69ng/ml. Keeping this concentration of remifentanil, the injection pain caused by propofol infusion was significantly reduced; patients feel comfortable, as there’re no serious adverse reactions, either.