Discontinuous monitoring of propofol concentrations in expired alveolar gas and in arterial and venous plasma during artificial ventilation

Background: Analyzing propofol concentration in expired alveolar gas (C(p)A) may be considered as a convenient, noninvasive method to follow the propofol concentration in plasma (CpPL). In the current study, the authors established procedures to measure C(p)A and CpPL for the assessment of their relation in two animal models during anesthesia. Methods: Expired alveolar gas and mixed venous and arterial blood were simultaneously sampled during continuous application of propofol for general anesthesia to three goats and three pigs. Propofol infusion rates were varied to modify plasma concentrations. C(p)A, sampled cumulatively over several respiratory cycles, was quantified by thermal desorption gas chromatography-mass spectrometry. CpPL was determined using reversed phase high-performance liquid chromatography with fluorescence detection. Results: c(p)A ranged from 0 to 1.4 and from 0 to 22 parts per billion in goats and pigs, respectively, at CpPL of 0-8 mu g/ml. The relation between C(p)A and CpPL was linear; however, the slopes of the regression lines varied between animals. Conclusion: Propofol can be quantified in expired alveolar gas. The results stress the role of marked species-specific variability.