Online breath analysis of propofol during anesthesia: clinical application of membrane inlet-ion mobility spectrometry

Background Breath analysis of propofol is a potential noninvasive method for approximating the plasma propofol concentration. There have been various reported techniques for measuring the exhaled propofol concentration at steady state; however, the propofol concentration undergoes marked changes during clinical anesthesia. Therefore, this study investigated the use of membrane inlet‐ion mobility spectrometry (MI‐IMS) to monitor exhaled propofol discontinuously and continuously during propofol anesthesia. Methods The study included 19 patients of American Society of Anesthesiologists physical status I or II. In experiment I (discontinuous study), breath and blood samples were collected discontinuously, with stable target propofol concentrations of 2.8 μg/ml, 3.2 μg/ml, 3.5 μg/ml, and 3.8 μg/ml. In experiment II (continuous study), propofol concentration was maintained at 3.5 μg/ml after induction, and exhaled breath was collected continuously every 3 min during propofol infusion. Relationships of the exhaled propofol concentration with the plasma propofol concentration, measured by high‐performance liquid chromatography and the continuously measured bispectral (BIS) index were investigated. Results Comparison of the exhaled and plasma propofol concentrations revealed a bias ± precision of 2.1% ± 14.6% (95% limits of agreement: − 26.5–30.7%) in experiment I and − 10.4% ± 13.2 (− 36.3–15.4%) in experiment II. In both experiments, exhaled propofol concentrations measured by MI‐IMS were consistent with, the propofol effect represented by the BIS index. Conclusions MI‐IMS may be a suitable method to predict plasma propofol concentration online during propofol anesthesia. Monitoring exhaled propofol may improve the safety of propofol anesthesia.