The electrode used by a transcutaneous CO2 monitor is the:

The electrode used by a transcutaneous CO2 monitor is the:

• A. Severinghaus electrode
• B. Clark electrode
• C. Vernier electrode
• D. Clark-Severinghaus electrode

Answer: (B)

Transcutaneous CO2 sensing uses the Severinghaus electrode. CO2 diffuses through a membrane into a bicarbonate-containing electrolyte; the dissolved CO2 forms carbonic acid, lowering the pH. A pH-sensitive electrode then converts that pH change into an electrical signal that correlates with the partial pressure of CO2 (pCO2). The Clark electrode, by contrast, measures oxygen via amperometric reduction, so it’s not the CO2 sensor. Some transcutaneous probes combine both sensors in one head (Clark-Severinghaus), but for measuring CO2 specifically, the Severinghaus element is the one that detects CO2 levels.

Transcutaneous CO2 sensing uses the Severinghaus electrode. CO2 diffuses through a membrane into a bicarbonate-containing electrolyte; the dissolved CO2 forms carbonic acid, lowering the pH. A pH-sensitive electrode then converts that pH change into an electrical signal that correlates with the partial pressure of CO2 (pCO2). The Clark electrode, by contrast, measures oxygen via amperometric reduction, so it’s not the CO2 sensor. Some transcutaneous probes combine both sensors in one head (Clark-Severinghaus), but for measuring CO2 specifically, the Severinghaus element is the one that detects CO2 levels.