Gas chromatograph-surface acoustic wave for quick real-time assessment of blood/exhaled gas ratio of propofol in humans.

Background: Although pilot studies have reported that exhaled propofol concentrations can reflect intraoperative plasma propofol concentrations in an individual, the blood/exhaled partial pressure ratio RBE varies between patients, and the relevant factors have not yet been clearly addressed. No efficient method has been reported for the quick evaluation of RBE and its association with inter-individual variables.
Methods: We proposed a novel method that uses a surface acoustic wave (SAW) sensor combined with a fast gas chromatograph (GC) to simultaneously detect propofol concentrations in blood and exhaled gas in 28 patients who were receiving propofol i.v. A two-compartment pharmacokinetic (PK) model was established to simulate propofol concentrations in exhaled gas and blood after a bolus injection. Simulated propofol concentrations for exhaled gas and blood were used in a linear regression model to evaluate RBE.
Results: The fast GC-SAW system showed reliability and efficiency for simultaneous quantitative determination of propofol in blood (correlation coefficient R(2)=0.994, P<0.01) and exhaled gas (R(2)=0.991, P<0.01). The evaluation of RBE takes <50 min for a patient. The distribution of RBE in 28 patients showed inter-individual differences in RBE (median 1.27; inter-quartile range 1.07-1.59).
Conclusions: Fast GC-SAW, which analyses samples in seconds, can perform both rapid monitoring of exhaled propofol concentrations and fast analysis of blood propofol concentrations. The proposed method allows early determination of the coefficient RBE in individuals. Further studies are required to quantify the distribution of RBE in a larger cohort and assess the effect of other potential factors.
Clinical Trial Registration: ChiCTR-ONC-13003291.
(© The Author 2014. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)