TRANSCUTANEOUS BLOOD-GAS MONITORING

Transcutaneous monitoring of blood gas involves the measurement of oxygen and carbon dioxide diffusion through the skin and estimates the arterial partial pressures of these gases. A one- to two-centimeter patch of skin is sealed off from the environment and heated to increase oxygen and carbon dioxide diffusion. Both gases diffuse through a semipermeable membrane and enter the electrolyte solution that surrounds the electrodes. Oxygen reacts with the cathode and produces a proportionate number of electrons. The electrons produce a current that is proportional to the transcutaneous oxygen level. Carbon dioxide reacts with water in the electrolyte solution to produce hydrogen ions. A potential difference between electrodes is produced; this difference logarithmically reflects carbon dioxide. Transcutaneous blood gas monitoring has been used recently to evaluate skin viability in reconstructive surgery and wound management, particularly in anesthetized or critically ill patients.