Clinical Practice
Precision and bias of target controlled propofol infusion for sedation

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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 μg 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 μg ml−1 one can predict the actual plasma concentration with 95% confidence only within a range of 0.44–1.38 μg ml−1.

Conclusions

This finding helps to explain differences in responses to propofol sedation; pharmacokinetic variability appears to be an important factor.

Keywords

anaesthetics, i.v., propofol
anaesthetic techniques, computer-assisted continuous infusion
equipment, infusion pump
model, computer
pharmacokinetics, model
statistics, regression analysis

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Presented in abstract format at the World Congress of Anaesthesiology, Paris, 2004.