Performance evaluation of a whole blood propofol analyser

The authors evaluated an analyser for the determination of propofol concentrations in whole blood. The Pelorus 1000 (Sphere Medical) measures propofol concentrations in around 5 min without the requirement for sample preparation. The performance of the analyser was characterised with respect to linearity, precision in control solutions and whole blood and method comparison to an HPLC based reference method. In addition, the effects of substances considered to potentially affect the assay method were investigated. The analyser was found to be linear up to 12 μg/ml (R2 = 0.9993), with a lower limit of quantification of 0.75 μg/ml. Total within device imprecision in control solutions was 0.11 μg/ml at 5.32 μg/ml and 0.17 μg/ml at 10.3 μg/ml. Within run precision in whole blood was 0.04 μg/ml at 2.84 μg/ml and 0.08 μg/ml at 6.68 μg/ml and for the reference method was 0.06 μg/ml and 0.12 μg/ml respectively. In comparison to the reference method, the overall bias of the Pelorus 1000 system over the range is estimated to be 0.15 μg/ml (95% confidence interval -0.11-0.41 μg/ml). The only cross interference of note is to a highly elevated level of conjugated bilirubin, while low haematocrit levels lead to a 0.13 μg/ml under reading with respect to the HPLC reference. The system fulfils the requirements for measurement of propofol concentrations in whole blood samples with precision and accuracy suitable for elucidating propofol pharmacokinetics at clinically relevant concentrations. With no requirement for sample preparation and a fast time to results, the analyser opens up the possibility of studies to measure and respond to blood propofol concentrations in patients in close to real time.