Awakening propofol concentration with and without blood-effect site equilibration after short-term and long-term administration of propofol and fentanyl anesthesia

Background: The propofol awakening concentration can vary. However, the effect site awakening propofol concentration will be a fixed value. The purpose of this study was to determine the awakening propofol concentrations obtained from infusion Schede using abrupt discontinuation of propofol (half-maximal effective concentration [EC(50)]) or a descending decrease in concentration to allow blood-effect site equilibration (EC(50)eq). Methods: Patients undergoing short-term (group 1) and long-term (group 2) elective surgery were anesthetized with computer-assisted continuous infusion of propofol and fentanyl with both groups receiving the same propofol (3 mu g/ml) and fentanyl (1 ng/ml) concentrations 20-30 min before the end of surgery until the end. Then both groups were further divided into two subgroups: subgroup A abrupt discontinuation, and subgroup B descending concentrations of propofol (15-min duration per concentration). In the A subgroups, the response to verbal command was evaluated every 30 s. In the B subgroups, the blood propofol concentrations just permitting and just preventing response to command were averaged individually. The EC(50) and EC(50)eq values were determined by probit analysis. Results: The EC(50) of group 1A was 1 mu g/ml which was significantly less than the 1.6 mu g/ml of group 2A (P < 0.05). The awakening time of group 1A was 5.2 +/- 1.8 min, which was significantly shorter than the 9.3 +/- 3.5 min of group 2A (means +/- SD). The EC(50)eq of both groups 1B and 2B was 2.2 mu g/ml. Conclusions: The EC(50)eq was independent of propofol infusion length, compared with the EC(50). Thus the potential for hysteresis during emergence from propofol anesthesia was confirmed.