Relationship between bispectral index, auditory evoked potential index and effect-site EC50 for propofol at two clinical end-points.
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.
Milne
S E
SE
University of Glasgow, Department of Anaesthesia, Glasgow Royal Infirmary, 10 Alexandra Parade, Glasgow G31 2ER, UK.
Troy
A
A
Irwin
M G
MG
Kenny
G N C
GN
D000328:Adult; D000556:Ambulatory Surgical Procedures / Q000379:methods; D000771:Anesthesia, Intravenous; D018686:Anesthetics, Intravenous / Q000008:administration & dosage / Q000097:blood*; D001364:Awareness / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D010812:Physical Stimulation; D015742:Propofol / Q000008:administration & dosage / Q000097:blood*
D018686:Anesthetics, Intravenous; D015742:Propofol