British Journal of Anaesthesia, 2003, Vol. 90, No. 2 127-131
© 2003 The Board of Management and Trustees of the British Journal of Anaesthesia
Clinical Investigations |
Relationship between bispectral index, auditory evoked potential index and effect-site EC50 for propofol at two clinical end-points
1 University of Glasgow, Department of Anaesthesia, Glasgow Royal Infirmary, 10 Alexandra Parade, Glasgow G31 2ER, UK. 2 University of Hong Kong, Queen Mary Hospital, Pokfulam Road, Hong Kong, China
Corresponding author: University of Michigan, Department of Anesthesiology, 1H247UH, PO Box 0048, 1500 East Medical Center Drive, Ann Arbor, Michigan 48109-9091, USA. E-mail: smilne@umich.edu 
Declaration of interest. Aspect Medical provided hardware and disposables to conduct this study. The hardware and software system used to calculate the AEPex was licensed by Glasgow University to AstraZeneca. Professor Kenny has acted as a consultant to AstraZeneca.
Background. Many anaesthetists are deterred from using total i.v. anaesthesia because of uncertainty over the concentration of propofol required to prevent awareness. We predicted blood and effect-site concentrations of propofol at two clinical end-points: loss of consciousness and no response to a painful stimulus.
Methods. Forty unpremedicated Caucasian patients were anaesthetized with i.v. propofol delivered by a Diprifusor target-controlled infusion (TCI). Bispectral index (BIS) and auditory evoked potential index (AEPex) were measured and blood and effect-site propofol concentrations were predicted. Logistic regression was used to estimate population values for predicted blood and effect-site propofol concentrations at the clinical end-points and to correlate these with BIS and AEPex.
Results. The effect-site EC50 at loss of consciousness was 2.8 µm ml–1 with an EC05 and an EC95 of 1.5 and 4.1 µm ml–1, respectively. The predicted EC50 when there was no response to a tetanic stimulus was 5.2 µm ml–1 with an EC05 and an EC95 of 3.1 and 7.2 µm ml–1, respectively.
Conclusions. Unconsciousness and lack of response to a painful stimulus occur within a defined range of effect-site concentrations, predicted by Diprifusor TCI software.
Br J Anaesth 2003; 90: 127–31
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