Fig. 4. Predicted concentration of fentanyl in the plasma over time after administration of an IV bolus of 2 µg/kg followed by demand boluses of 15 µg every 15 minutes and background infusion of 15 µg/h. (A) The entire time–concentration curve. (B) Time–concentration curve of time to reach MEAC. (C) Time–concentration curve of time to reach 90% steady-state concentration of fentanyl. MEAC: minimum effective analgesic concentration, MEC: minimum effective concentration. Demand bolus, background infusion rate, and lock-out time of postoperative IV patient-controlled analgesia (IV PCA) were set at 1 ml, 1 ml/h, and 15 minutes, respectively. The concentration of fentanyl in IV PCA was 15 µg/ml. The pharmacokinetic model of Scott et al. was applied to this simulation [44]. Vertical dotted lines indicated time to reach MEAC (6 hours) and 90% steady-state concentration (18.5 hours). Time 0 indicates 1 hour before the end of surgery.
