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 R-BE varies between patients, and the relevant factors have not yet been clearly addressed. No efficient method has been reported for the quick evaluation of R-BE 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 R-BE. 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 R-BE takes <50 min for a patient. The distribution of R-BE in 28 patients showed inter-individual differences in R-BE (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 R-BE in individuals. Further studies are required to quantify the distribution of R-BE in a larger cohort and assess the effect of other potential factors.