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ANESTHETIC PHARMACOLOGY

Individual Effect-Site Concentrations of Propofol Are Similar at Loss of Consciousness and at Awakening

Department of Anesthesiology, Tokyo Women’s Medical University, Tokyo, Japan; Department of Anesthesiology, University of Yamanashi, Faculty of Medicine, Yamanashi, Japan; and Outcomes Research^TM Institute and Departments of Anesthesiology and Perioperative Medicine and Pharmacology, University of Louisville, Louisville, Kentucky.

Address correspondence and reprint requests to Professor Ozaki, Department of Anesthesiology, Tokyo Women’s Medical University, Tokyo 162–8666, Japan. Address e-mail to mozaki{at}anes.twmu.ac.jp

Reported effect-site concentrations of propofol at loss of consciousness and recovery of consciousness vary widely. Thus, no single concentration based on a population average will prove optimal for individual patients. We therefore tested the hypothesis that individual propofol effect-site concentrations at loss and return of consciousness are similar. Propofol effect-site concentrations at loss and recovery of consciousness were estimated with a target-control infusion system in 20 adults. Propofol effect-site concentrations were gradually increased until the volunteers lost consciousness (no response to verbal stimuli); unconsciousness was maintained for 15 min, and the volunteers were then awakened. This protocol was repeated three times in each volunteer. Our major outcomes were the concentration producing unconsciousness and the relationship between the estimated effect-site concentrations at loss and recovery of consciousness. The target effect-site propofol concentration was 2.0 ± 0.9 at loss of consciousness and 1.8 ± 0.7 at return of consciousness (P < 0.001). The average difference between individual effect-site concentrations at return and loss of consciousness was only 0.17 ± 0.32 µg/mL (95% confidence interval for the difference 0.09–0.25 µg/mL). Our results thus suggest that individual titration to loss of consciousness is an alternative to dosing propofol on the basis of average population requirements.

IMPLICATIONS: Propofol can be titrated to the concentration that produces consciousness in individual patients. Provided that the propofol effect-site concentration does not much exceed the concentration initially required to produce unconsciousness, patients can be expected to awaken quickly on completion of the procedure.

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