Intra-arterial blood gas sensors usually use a single or double fiber configuration. Typically, the matrix containing the indicator is attached to the end of the optical fiber. Because the solubility of O2 and CO2 gases, as well as the optical properties of the sensing chemistry itself, is affected by the temperature variations, fiber optic intravascular sensors include a thermocouple or thermistor wire running alongside the fiber cable to monitor and correct for temperature fluctuations near the sensor tip. A nonlinear response is characteristic of most chemical indicator sensors. Thus, the operating range of these sensors is normally optimized to match the range of concentrations according to the intended application.
Intra-arterial fiber optic blood gas sensors are typically placed inside a standard 20-gauge arterial cannula that is sufficiently small, thus allowing adequate spacing between the sensor and the catheter wall. The resulting lumen is large enough to permit the withdrawal of blood samples, introduction of a continuous or intermittent anticoagulant (e.g. heparin) flush and the recording of a blood pressure waveform. Additionally, the optical fibers are encased in a protective tubing to contain any fiber fragments in case they break off. The material in contact with the blood is typically treated with a covalently bonded layer of heparin, resulting in low susceptibility to fibrin deposition.
Also Read: The Operation of Fiber-optic Based Blood Gas Sensors
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