RESUMEN
BACKGROUND: The main advantage of drug administration by target-controlled infusion (TCI) is that it allows rapid adjustments of blood concentrations to individual patients requirements. In this study, we tried to confirm the side effects, relation, safety range and minimum effective analgesic concentration (MEAC) of fentanyl at the effect site. METHODS: Sixty ASA physical status 1 or 2 patients (age: 20 - 50 years) undergoing orthopedic surgery with regional anesthesia were randomly allocated to one of three groups according to effect site concentration of fentanyl (1, 1.5, or 2 ng/ml, n = 20 for each group). Total infusion time, total amount of drugs, vital signs, muscular rigidity, respiratory depression, level of consciousness, nausea, vomiting and pruritus was investigated. Meanwhile, we evaluated the MEAC by checking the effect site concentration of fentanyl when the patient complained of pain following propofol-fentanyl-N2O anesthesia using a computer assisted continuous infusion (n = 30). RESULTS: Demographic data and averaging scores of each parameter showed no difference among groups. However, incidences tended to increase above 1.5 ng/ml except with rigidity in the 1.5 ng/ml fentanyl group. The MEAC of fentanyl was checked as 0.61 +/- 0.18 ng/ml. CONCLUSIONS: Estimated MEAC of fentanyl was 0.61 +/- 0.18 ng/ml. There were increased side effects and complaints of patients above 1.5 ng/ml. The optimal initial postoperative target concentration of fentanyl was considered as 1 ng/ml.