Sensing blood gases

Lubbers / Opitz 1975 quenching of pyrenebutyric acid in teflon-covered solution applied to blood gas sensing... 

How can phase-modulation fluorometry contribute to this health-care need It now seems possible to construct a lifetime-based blood gas catheter (Figure 1.3), or alternatively, an apparatus to read the blood gas in the freshly drawn blood at the patient s bedside. To be specific, fluorophores are presently known to accomplish the task using a 543-nm Green Helium-Neon laser,(18 19) and it seems likely that the chemistries will be identified for a laser diode source. The use of longer wavelengths should minimize the problems of light absorption and autofluorescence of the samples, and the use of phase or modulation sensing should provide the robustness needed in a clinical environment. For the more technically oriented researcher, we note that the... 

Quality Control Data. Data obtained from assays of blood gas and pH control materials may be handled in the same way as data from other clinical chemistry determinations (i.e., mean, SD, and coefficient of variation, and control and confidence limits for construction of Levey-Jennings plots). As stability of commercial aqueous control materials is generally several months, vendors often provide data reduction programs that standardize and simplify documentation. However, the resulting reports are temporally delayed and are most useful for meeting accreditation requirements as opposed to real-time corrective or preventive action. They are however useful to compare long-term performances with other laboratories. Equally important features of quality assurance to an active blood gas service are the sixth sense of practiced operators for detecting subtle manifestations of deterioration of instrument performance and the suspicion of trouble expressed by clinicians. 

Sensor temperature coefficient and time response are also variables to be understood. Temperature may shift the pKa of the dye and change the cell thickness, and will certainly affect the actual value of the blood gas variables of the blood that is adjacent to the sensor. For these reasons, a complete blood gas sensor includes a local temperature sensor, particularly if the sensor is to be placed in a peripheral artery where local temperature may not be equal to central body temperature. The chemical sensor temperature coefficient must be well characterized so that it will accurately measure the local blood gas value. Bench analysers usually measure blood samples at 37 °C so the in vivo system must then adjust the measured value to that temperature. The temperature coefficient of the blood gas variables, in blood, may be several percent per degree, and, in the case of Foj, depend very strongly on the actual value. Thus, to make the in vivo sensor agree with bench analysers, local temperature sensing must have an accuracy of better than 1 °C. Size and accuracy requirements can be met by a miniature thermocouple. The system designer has to make sure that the temperature circuit can handle the microvolt signals with adequate accuracy and stability as well as meet patient electrical isolation requirements. 

Another microcell has been proposed that may be used as a microcell for pseudo-continuous sensing, or as a disposable blood gas analyzer [13], Three sensor spots, responsive to, respectively, pH, oxygen and carbon dioxide, are placed in a 30-pL... 

In 1954, the first pC02 sensor was introduced by Stow and Randall [18]. Severinghaus and Bradley [19] have optimized this sensing concept and pubhshed a CO2 sensor suitable for routine laboratory use one year later. These Severinghaus-type probes are still the sensors of choice for PCO2 monitoring in modem blood gas analyzers. 

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