Breath-by-breath measurement of intraoperative propofol by unidirectional anisole-assisted photoionization ion mobility spectrometry via real-time correction of humidity

Development and validation of a novel UV-TOF MS method for real-time exhaled propofol analysis in Beagles

Propofol, a fast-acting anesthetic, requires precise titration to minimize adverse effects. While plasma-based monitoring is slow, exhaled propofol offers a real-time, non-invasive alternative, though its clinical application remains limited. This study evaluates ultraviolet time-of-flight mass spectrometry (UV-TOF MS) for real-time monitoring, presenting its calibration and validation in Beagle dogs. Calibration showed excellent linearity (R2 = 0.9939) over 3.23-46.13 ppbv. The intra-day imprecision at propofol concentrations of 4.61 and 23.06 ppbv was below 5.83% and 7.75%, respectively, while the inter-day imprecision was 9.69% and 9.75%, respectively. Carry-over effects were minimal, with signal recovery within 40-60 s, measuring 8.7%, 9.1%, and 4.7% at 4.61, 9.30, and 23.06 ppbv, respectively. In Beagle dogs, Cexhaled exhibited a moderately strong linear correlation with Cplasma (R2 = 0.7950) and a moderate correlation with sedative effects, as indicated by the bispectral index (R2 = 0.5501) after a single bolus injection. Pharmacokinetic (PK) analysis revealed a delay in peak concentration (Tmax) for Cexhaled (2.00 ± 0.21 min) compared to Cplasma (1.00 ± 0.00 min). While AUC values were not directly comparable, both exhibited R_AUC > 80%, indicating reliable drug kinetic reflection. Mean residence time (MRT) and elimination rate constants (λz) showed no significant differences. These results suggest that exhaled breath analysis provides pharmacokinetic insights comparable to plasma, with a slight delay in peak concentration. UV-TOF MS proved to be an efficient method for detecting exhaled propofol, offering potential for real-time anesthesia monitoring in clinical settings.

Developing a PK-PD model for propofol in exhaled air and the BIS following fospropofol disodium in beagles

BACKGROUND

Fospropofol, a water-soluble prodrug of propofol, is metabolized into propofol by alkaline phosphatase after administration. This study aimed to develop a pharmacokinetic-pharmacodynamic (PK-PD) model that correlates the propofol concentration in exhaled air (Ce-pro-f) with its anesthetic effects, as measured by the bispectral index (BIS) in beagles.

METHODS

Beagles receiving a single intravenous infusion of fospropofol at varying doses were divided into three groups (n = 6): the DBL-fospro group (15 mg/kg), the DBM-fospro group (30 mg/kg), and the DBH-fospro group (60 mg/kg). Propofol levels were monitored using VUV-TOF MS from pre-administration to recovery. Correlations between Ce-pro-f and blood concentration (Cblood-pro), as well as between Ce-pro-f and the BIS were investigated. PK, PD, and PK-PD models describing the relationship between Ce and BIS were also analyzed.

RESULTS

Propofol concentration in exhaled air can be quantified using VUV-TOF MS at a mass-to-charge ratio of 177.6. After fospropofol injection, the peak Ce-pro-f was delayed compared to Cblood-pro. The PK model of Ce-pro-f can be described using a noncompartmental approach, corresponding to the linear PK characteristics. Additionally, Ce-pro-f showed a moderate to strong negative correlation with BIS values. In the PK-PD model, the PK component was well characterized by a two-compartment model incorporating a first-order delay to account for the time lag of Ce-pro-f relative to Cblood-pro. The PD component was well fitted by the inhibitory sigmoid Emax model, with an indirect connection model selected to explain the observed lag between BIS signals and Ce-pro-f peaks.

CONCLUSIONS

This study is the first to develop a PK-PD model for exhaled propofol in beagles after fospropofol disodium administration. The PK profile was described by a two-compartment model with a first-order delay, and the PD profile was modeled using an inhibitory sigmoid Emax model with an indirect connection model to capture the lag between BIS and exhaled propofol peaks.

Online monitoring of propofol concentrations in exhaled breath

Propofol, a widely used intravenous anesthetic agent, requires accurate monitoring to ensure therapeutic efficacy and prevent oversedation. Recent developments in modern analytical instrumentation have led to significant breakthroughs in on-line analysis of exhaled breath. This review discusses several sophisticated analytical methods that have been explored for noninvasive, real-time monitoring of propofol concentrations, including proton transfer reaction mass spectrometry, selected ion flow tube mass spectrometry, ion mobility spectrometry, and gas chromatography coupled to surface acoustic wave sensors. These techniques have demonstrated good correlations between plasma and exhaled propofol concentrations and between exhaled propofol concentrations and its cerebral effects. Despite these advances, the use of these technologies in clinical settings is hampered by challenges such as equipment noise, bulkiness, and high cost, as well as limitations related to endotracheal intubation, strong adsorption of propofol to components of the respiratory circuit, variability in respiratory patterns, susceptibility to changes in pulmonary ventilation and blood flow, inconsistencies in calibration methods, and the influence of other drugs and temperature fluctuations on measurement accuracy. Overcoming these technical and procedural challenges is critical to advancing the clinical application of breath analysis for propofol monitoring. This article reviews published studies and summarizes the progress and ongoing challenges in the field.

Humidity and measurement of volatile propofol using MCC-IMS (EDMON)

The bedside Exhaled Drug MONitor - EDMON measures exhaled propofol in ppbv every minute based on multi-capillary column - ion mobility spectrometry (MCC-IMS). The MCC pre-separates gas samples, thereby reducing the influence of the high humidity in human breath. However, preliminary analyses identified substantial measurement deviations between dry and humid calibration standards. We therefore performed an analytical validation of the EDMON to evaluate the influence of humidity on measurement performance. A calibration gas generator was used to generate gaseous propofol standards measured by an EDMON device to assess linearity, precision, carry-over, resolution, and the influence of different levels of humidity at 100% and 1.7% (without additional) relative humidity (reference temperature: 37°C). EDMON measurements were roughly half the actual concentration without additional humidity and roughly halved again at 100% relative humidity. Standard concentrations and EDMON values correlated linearly at 100% relative humidity (R²=0.97). The measured values were stable over 100min with a variance ≤ 10% in over 96% of the measurements. Carry-over effects were low with 5% at 100% relative humidity after 5min of equilibration. EDMON measurement resolution at 100% relative humidity was 0.4 and 0.6 ppbv for standard concentrations of 3 ppbv and 41 ppbv. The influence of humidity on measurement performance was best described by a second-order polynomial function (R²≥0.99) with influence reaching a maximum at about 70% relative humidity. We conclude that EDMON measurements are strongly influenced by humidity and should therefore be corrected for sample humidity to obtain accurate estimates of exhaled propofol concentrations.

High-resolution mass spectrometry exhalome profiling with a modified direct analysis in real time ion source

RATIONALE

Exhaled breath contains many substances that are closely related to human metabolism. Analysis of its composition is important for human health, but it is difficult. Since the volatile molecules in breath samples are exhaled instantaneously, easily diffused and modified, and at low level of presence, they are difficult to identify and quantify.

METHODS

A modified direct analysis in real time ion source was used for high-resolution mass spectrometry measurement of human metabolites in exhaled breath through online monitoring and offline analysis, in both positive and negative ion modes. The improved system enabled the breath volatiles as well as condensates to be directly sampled, rapidly transmitted and efficiently ionized in a confined region, and then detected using an Orbitrap mass analyzer.

RESULTS

The molecular features with online and offline analysis of exhaled breath were demonstrated with obvious differences. A total of about 65 metabolites in positive ion mode and about 55 metabolites in negative ion mode were identified based on accurate m/z values. Exhalome profile and the composition proportion of different classes of compounds were obtained. The relative contents of metabolites from breath varied during different time periods throughout a day.

CONCLUSIONS

A more complete picture of the human breath metabolome was provided combining the results obtained from both online and offline analysis. The developed method allows analysis of breath samples with different status rapidly and directly, and it features simple operation and metabolite identification, requiring little or no sample preparation.