Arterial pH monitoring with monocrystalline antimony sensors

Abstract

Monocrystalline antimony catheter electrodes were studied intra-arterially in non-heparinized dogs. The sensitivity for variations in arterial Po₂ (P_ao₂) was evaluated for this kind of metal-metal oxide pH sensor. The influence of P_ao₂ 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 P_ao₂, a non-linear relation was found for the P_ao₂ 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 P_ao₂ in the range 2.9 kPa < P_ao₂ < 10 kPa, and 20.7 mV/log₁₀ P_ao₂ in the range 10 kPa < P_ao₂ < 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 P_ao₂ variations which is closely correlated to the haemoglobin-oxygen dissociation function. When compensation for P_ao₂ variations was performed on an earlier evaluated study over a wide pH range but limited P_ao₂ range, the pH sensitivity previously found was not influenced.

Key-words:

• blood gases
• in vivo
• metal-metal oxide
• oxygen sensitivity
• pH electrode
• polycrystalline antimony