CO₂Electrodes

Abstract

The CO 2 electrode is a membrane covered glass pH electrode with an internal electrolyte film containing NaCl and NaHCO 3 . The electrical output is a log function of p CO 2 (partial pressure) exposed to the sensor face. At 37°C, output is 60 mV for a 10‐fold change in p CO 2 . The CO 2 electrode was invented by Richard Stow, Ph.D. at Ohio State University Hospital in 1954 to help with management of paralyzed polio victims who were being artificially ventilated. His original device failed because his internal electrolyte was distilled water. Severinghaus added bicarbonate and salt to stabilize it. Manufacture of the device began in 1959. Transcutaneous (tc) CO 2 electrodes were introduced in the mid‐1970s when transcutaneous O 2 electrodes were found to adequately reflect arterial blood oxygen pressure ( p aO 2 ), especially in premature infants whose immature lungs required extra oxygen, but where too much oxygen caused blindness. The tc p CO 2 electrodes are combined with tc p O 2 electrodes in a single small sensor that is attached with adhesive to skin surfaces. These devices are internally heated to increase local skin blood flow. At 43–45°C, skin surface p O 2 resembles (arterial) p aO 2 , but skin surface tc p CO 2 is ∼ 1.4 times higher than p aCO 2 . The instrument is calibrated to correct this difference. Transcutaneous oxygen and carbon dioxide electrodes have found many uses in addition to their use for newborn infants. However, their usefulness fell after pulse oximetry became common in 1985. The electrodes need careful maintenance with membrane changes and limitation of time on a skin location, to avoid burns.

Carbon dioxide monitoring in the newborn infant

“…The sensors work by detecting changes in the electrode pH, 31 with heating of the transcutaneous sensors to a recommended temperature of 42–44°C at the surface of the skin inducing an increase in arterial blood flow to the capillary bed, thereby detecting the concentration of carbon dioxide as diffusion occurs at the skin surface 30,32,33 . Due to the high temperature and contribution of locally produce CO 2 from epidermal cells 32 carbon dioxide values produced by transcutaneous monitoring are higher than simultaneously measured arterial levels by a factor of about 1.4, 34 therefore, transcutaneous sensors are manufactured with a correction algorithm and perform internal calibration to account for such differences in measurement 35 …”