Relationship between bispectral index, auditory evoked potential index and effect-site EC50 for propofol at two clinical end-points

Br J Anaesth. 2003 Feb;90(2):127-31. doi: 10.1093/bja/aeg035.


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 EC(50) at loss of consciousness was 2.8 micro m ml(-1) with an EC(05) and an EC(95) of 1.5 and 4.1 micro m ml(-1), respectively. The predicted EC(50) when there was no response to a tetanic stimulus was 5.2 micro m ml(-1) with an EC(05) and an EC(95) of 3.1 and 7.2 micro m 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.

MeSH terms

  • Adult
  • Ambulatory Surgical Procedures / methods
  • Anesthesia, Intravenous*
  • Anesthetics, Intravenous / administration & dosage
  • Anesthetics, Intravenous / blood*
  • Awareness / physiology
  • Dose-Response Relationship, Drug
  • Electroencephalography*
  • Evoked Potentials, Auditory / drug effects*
  • Evoked Potentials, Auditory / physiology
  • Female
  • Humans
  • Logistic Models
  • Male
  • Middle Aged
  • Physical Stimulation
  • Propofol / administration & dosage
  • Propofol / blood*


  • Anesthetics, Intravenous
  • Propofol