Severinghauselektrode

Severinghauselektrode, commonly referred to in English as the Severinghaus CO2 electrode, is a gas-sensing device used to determine the partial pressure of carbon dioxide (pCO2) in blood as part of arterial blood gas analysis. The electrode operates with a CO2-permeable membrane that separates a bicarbonate buffer from the blood sample. CO2 diffuses across the membrane into the buffer, where it forms carbonic acid and lowers the pH. An internal pH-sensitive glass electrode measures this pH change, and the resulting signal is converted to pCO2 using the known buffer composition and temperature, via the Henderson–Hasselbalch relationship.

History and development: The Severinghauselektrode was developed by Louis H. Severinghaus and colleagues in the late 1950s to early 1960s as a practical means to measure CO2 directly in blood. It represented a key advance in rapid blood gas analysis and became a standard component of many automated blood gas analyzers for several decades.

Construction and operating principles: A typical Severinghaus electrode consists of a sealed chamber containing a fixed bicarbonate buffer, a CO2-permeable membrane on one side, and a pair of electrodes—a pH-sensitive glass electrode and a reference electrode—inside the chamber. CO2 from the blood diffuses through the membrane into the buffer, lowering the pH. The pH electrode yields a signal that, after temperature compensation and calibration, is converted into pCO2. The system requires regular calibration with gas standards or bicarbonate solutions to maintain accuracy.

Applications and limitations: Severinghaus electrodes have been used in hospital-based and point-of-care blood gas analyzers to provide rapid pCO2 measurements alongside pO2 and pH. Limitations include membrane fouling and drift, the need for routine calibration and maintenance, and buffer stability concerns. With advances in optical and amperometric CO2 sensing, Severinghaus-type sensors remain part of historical and some contemporary systems, though many platforms employ alternative sensing technologies.