Abstract
Antimony oxide (Sb-SbOx) and pH-sensitive glass electrodes, combined with reference electrodes, surrounded by electrolyte and covered with gas permeable membrane (gpm) were used for transcutaneous PCO2(PtcCO2) measurement. A servo-controlled heater unit maintained sensor temp, and produced local hyperemia. A thermistor was placed under the gpm to measure true sensor temp. O2 sensitivity of Sb-SbOx electrode was reduced greatly in the 65-175 mm Hg PO2 range by cell loading, but below 65 mm Hg, O2 sensitivity was significant. The pH-sensitive glass electrode was preferred due to its insensitivity to O2. After the sensor was placed on the skin of rabbits, it was calibrated in situ and its temp, coefficient established. This was repeated at the end of the 6-hr. experiment. For the best correlation between PaCO2 and PtcCO2, the skin surface temp, was maintained between 40-42°C, as lower temps, made ptcCO2 higher. Based on in situ calibration, the fitted regression line had a slope of 1.029, intercept of -4.39, and SE of 4.14 mm Hg PCO2. In the range of 21-75 mm Hg, PtcCO2 was 2.2 - 3.8 mm Hg below PaCO2. Based on in situ calibration with one point PaCO2, calibration, the line had a slope of 1.0, intercept of 0.6, SE of 3.4 mm Hg PCO2, and linear regression coefficient of 1.0. These data indicate the usefulness of PtcCO2 monitoring to indicate PaCO2 changes under normal physiologic conditions.
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