Reducing System Response Time and Noise of Electrochemical Gas Sensors: Discussed for Propofol Monitoring in Breathing Gas

Electrochemical sensors are used in various gas measurement applications and are available for different gases. Depending on the application, the sensor might need to be installed far away from the actual measurement site, requiring the use of long sampling lines. Examples are portable gas measurement devices in which remote locations like tanks and chemical reactors need to be monitored. But also medical applications, where the sensors cannot be positioned in close vicinity to the patient, are common like, e.g., the side-stream measurement of breathing gas. Due to the characteristics of electrochemical sensors and to the adsorption and desorption behavior of sampling lines for different gases, the electrical sensor signal may indicate long response times. In this paper, we propose an on-line signal processing algorithm which is capable to significantly improve the performance. After characterizing the dynamic behavior of the sensor system, a properly designed deconvolution filter is used to reduce response time and signal noise. Within this article, we also provide an example of this algorithm for a novel electrochemical sensor for the measurement of the anesthetic agent propofol in exhaled air. For this application, the acceleration is prerequisite for the measurement chain to be of practical use in a clinical setting. Our goals, to establish a measurement three times faster than the physiologic parameter might change and to reduce non-physiological disturbances, were achieved with additional reserves.