The measuring electrode buffer for a pCO2 electrode is usually which buffer?

• A. Bicarbonate buffer
• B. Saline
• C. Phosphate buffer
• D. Citrate buffer

Answer: (A)

The measuring electrode buffer for a pCO2 electrode is a bicarbonate buffer. The sensor works by letting CO2 diffuse into the buffer, where CO2 plus water forms carbonic acid that quickly dissociates to H+ and HCO3-. This changes the pH in a way that is directly related to the CO2 level, and the pH electrode then converts that change into a pCO2 reading. Using bicarbonate is essential because it is the natural CO2/HCO3− buffering system in blood, so the relationship between CO2 concentration and pH is predictable and reliable for measurements. Saline would not buffer pH, and phosphate or citrate buffers do not participate in the CO2 hydration/ dissociation in the same physiologically relevant way, making them unsuitable for this purpose.