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

Abstract

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 [EC50]) or a descend- ins decrease in concentration to allow blood-effect site equilibration (EC50eq). 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 μg/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 EC50 and EC50eq values were determined by probit analysis. Results: The EC50 of group 1A was 1 μg/ml, which was significantly less than the 1.6 μg/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 EC50eq of both groups lB and 2B was 2.2 μg/ml. Conclusions: The EC50eq was independent of propofol infusion length, compared with the EC50. Thus the potential for hysteresis during emergence from propofol anesthesia was confirmed.