Ion-molecule reaction mass spectrometry may allow the continuous and noninvasive monitoring of expiratory propofol levels in patients undergoing general anesthesia.
Propofol in exhaled breath can be detected and monitored in real time by ion molecule reaction mass spectrometry (IMR-MS). In addition, propofol concentration in exhaled breath is tightly correlated with propofol concentration in plasma. Therefore, real-time monitoring of expiratory propofol could be useful for titrating intravenous anesthesia, but only if concentration changes in plasma can be determined in exhaled breath without significant delay. To evaluate the utility of IMR-MS during non-steady-state conditions, we measured the time course of both expiratory propofol concentration and the processed electroencephalography (EEG) as a surrogate outcome for propofol effect after an IV bolus induction of propofol. Twenty-one patients scheduled for routine surgery were observed after a bolus of 2.5 mg kg(-1) propofol for induction of anesthesia. Expiratory propofol was measured using IMR-MS and the cerebral propofol effect was estimated using the bispectral index (BIS). Primary endpoints were time to detection of expiratory propofol and time to onset of propofol's effect on BIS, and the secondary endpoint was time to peak effect (highest expiratory propofol or lowest BIS). Expiratory propofol and changes in BIS were first detected at 43 ± 21 and 49 ± 11 s after bolus injection, respectively (P = 0.29). Peak propofol concentrations (9.2 ± 2.4 parts-per-billion) and lowest BIS values (23 ± 4) were reached after 208 ± 57 and 219 ± 62 s, respectively (P = 0.57). Expiratory propofol concentrations measured by IMR-MS have similar times to detection and peak concentrations compared with propofol effect as measured by the processed EEG (BIS). This suggests that expiratory propofol concentrations may be useful for titrating intravenous anesthesia.
Analysis of volatile organic compounds (VOCs) in exhaled breath offers diagnostic potential in research and clinical medicine. Mass spectrometry of expiratory air allows VOC measurements in a concentration range from parts per trillion to parts per million. For the reduction of dilution-related measurement errors due to dead space admixture, the precise identification of the end-expiratory phase of expiration is essential. We used a combination of two integrated MS systems consisting of a conventional MS capable of fast CO(2) tracing controlling a second, highly sensitive MS for the measurement of VOCs based on ion-molecule-reaction-MS (IMR-MS). This study intended to test the applicability of a software-based method of CO(2)-controlled alveolar breath-gas sampling in 12 ventilated patients using acetaldehyde, acetone, ethanol and isoprene as target VOCs (IMR-MS compound integration time 500 ms, cycle time 2 ms, measurement time 120 min). CO(2)-controlled versus mixed inspiratory/expiratory results are as follows: acetaldehyde 71* (61-133) versus 63 (47-87); acetone 544* (208-1174) versus 504 (152-950); ethanol 133 (99-166) versus 123 (108-185); isoprene 118* (69-253) versus 58 (44-112) (values in ppbv as medians with 25-75%; *p < 0.05 versus mixed inspiratory/expiratory values). The applied software-based CO(2)-controlled sampling method of expiratory air resulted in significant higher concentrations of acetaldehyde, acetone and isoprene.
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