Precision and bias of target controlled propofol infusion for sedation.

Background: The purpose of this study is to test precision and systematic bias of a target controlled infusion (TCI) of propofol in human volunteers at two sedative concentrations.
Methods: We studied the 'Diprifusor' model (Marsh Pharmacokinetics and a Graseby 3400 infusion pump) in 18 human volunteers at two sedative target plasma concentrations (0.5 and 1.0 microg ml(-1)). Twenty minutes after infusion start or change and 20 min after discontinuation of the infusion plasma propofol concentrations were measured using liquid chromatography-mass spectroscopy (LC-MS). Plasma propofol concentrations were compared with concentrations predicted by the TCI system. Agreement of those two measures (precision and bias) was determined using regression analysis.
Results: We found little systematic bias but poor precision. When setting the TCI system to deliver a plasma concentration of 1.0 microg ml(-1) one can predict the actual plasma concentration with 95% confidence only within a range of 0.44-1.38 microg ml(-1).
Conclusions: This finding helps to explain differences in responses to propofol sedation; pharmacokinetic variability appears to be an important factor.