A Real-time Monitoring System Based On Fast Gas Chromatography And Acoustic Wave Sensor (GC-SAW) For Exhaled Anesthetic Propofol

Nowadays propofol has become a widely used clinical anesthetic. And there is a requirement of more efficient method for real-time propofol monitoring. Due to the convenience, non-invasive and no side-effect, respiratory monitoring is becoming a new effective clinical monitoring method. For this reason, we proposed a real-time and on-site clinical exhaled propofol monitoring method which is based on fast gas chromatography and surface acoustic wave sensor (GC-SAW). The content of this article is divided into the following parts:1. The introduction of SAW and the structure of pneumatic system. Firstly by the principle of SAW, a SAW sensor which can be used in exhaled gas detection was designed. Its theoretical sensitivity is8756Hz/ng. Then provided a modularized gas chamber design for SAW to work in a stable environment. Finally the principle of GC, the system’s working process of gas sampling, adsorption enrichment and GC gas separation was introduced.2. Design of GC-SAW circuit. Two MSP430cored circuits was used in the system. With the innovative directly resistive-heating method, the temperature accuracy of GC column was0.1℃, while the heating speed had reached10℃/s, with an accuracy of0.5℃/s. Thus improved the efficiency and volume of the system to realize the real-time detection and portability. Besides we also achieved the precise temperature control of gas chamber and other modules. The temperature accuracy of gas chamber had reached0.02℃/s to eliminate the interference of the temperature. And with the novel ultrafast Tenax TA sorbent tube heating, the compounds desorbed within50ms, which dramatically improved the GC separation in a short column. What’s more, we completed the SAW sensor oscillation, frequency mixing and signal detection and realized the detection with a sampling rate of50/s and0.5Hz accuracy. Finally I introduced the control and communication circuit of six-way valves, mass flow controllers, cooling fans and pumps.3. Software systems of GC-SAW. We completed the programs of the two MSP430circuits. The convenient PC client software with a user friendly interface was completed. Communication protocols between MSP430and PC, efficient algorithm for SAW signal’s peak recognition and calculation, and function of automation were also realized.4. The clinical experiments by fast GC-SAW for exhaled propofol. By calibration, GC-SAW showed excellent linearity in the detection of propofol gas sample and blood sample. And the results of28patient’s exhaled and blood propofol detection demonstrated a strong correlation (0.949) with each other, as well as great correlations with pharmacokinetic models for exhaled gas and blood (0.995and0.992respectively). Besides6patients’ exhaled results showed a strong correlation with TCI. All the clinical experiments above proved the exhaled gas can effectively reflect the patient’s propofol changes and fast GC-SAW is a promising method for clinical exhaled propofol monitoring.