Transcutaneous monitoring is noninvasive and relatively simple to use. In neonates and small infants, this monitoring technique may provide very useful clinical information. Transcutaneous gas monitoring, using conventional electrochemical techniques, provides a means of trending the values of PaO2 and PaCO2 in most patients with relatively normal cardiovascular function. In patients with compromised cardiopulmonary function and in many adults, because of different skin structure, transcutaneous gas monitoring will not accurately reflect arterial blood gas tensions. Because transcutaneous gases depend on skin perfusion, however, it may be useful in monitoring tissue perfusion, especially in patients with peripheral vascular disease and tissue flaps. The heating of the monitoring probe necessitates frequent site changes to avoid thermal injury, which make it more labor intensive than other noninvasive monitoring methods.