Arterial pH monitoring with monocrystalline antimony sensors. A study of sensitivity for PO2 variations.

Monocrystalline antimony catheter electrodes were studied intra-arterially in non-heparinized dogs. The sensitivity for variations in arterial PO2 (PaO2) was evaluated for this kind of metal-metal oxide pH sensor. The influence of PaO2 compensation on a previous pH sensitivity estimate was calculated. When the mV signal from the antimony sensor, after compensation for pH and temperature variations, was expressed as a function of log10 PaO2, a non-linear relation was found for the PaO2 range studied, 2.9-50 kPa. After calculations this range was divided into a lower and a higher sub-range. A first-order linear approximation was applied for these subranges. The sensitivity for oxygen was 70 mV/log10 PaO2 in the range 2.9kPa less than PaO2 less than 10 kPa, and 20.7 mV/log10 PaO2 in the range 10 kPA less than PaO2 less than 50 kPa. The non-logarithmic sensitivity for intra-arterial oxygen is contradictory to results from in vitro studies in test solutions. The present study indicates that the monocrystalline antimony pH sensor has a sensitivity for PaO2 variations which is closely correlated to the haemoglobin-oxygen dissociation function. When compensation for PaO2 variations was performed on an earlier evaluated study over a wide pH range but limited PaO2 range, the pH sensitivity previously found was not influenced.