Comparison of transcutaneous oxygen tension with arterial oxygen tension in newborn infants with severe respiratory illnesses.

Transcutaneous oxygen tension (tcPO2), measured by two skin electrodes of different design, and arterial oxygen tension (PaO2), measured by an intravascular oxygen electrode, were continuously recorded for periods of six hours in 15 newborn infants with serious respiratory illnesses. Ten of the infants needed mechanical ventilation and three needed continuous positive airway pressure. One skin electrode had three microcathodes surrounded by a heated ring-shaped anode, and the other had a large heated cathode. The temperature of both electrodes was set at 44 degrees C and they were calibrated in vitro. The tcPO2 recorded by the electrode with the microcathodes was found to estimate PaO2 reasonably accurately for the whole six-hour duration of the study. The tcPO2 recorded by the electrode with the large cathode gave a similar estimate of PaO2 for three hours, but then tcPO2 often fell relative to PaO2. This fall was probably caused by skin changes at the electrode site. For a variety of reasons, our results suggest that measurement of tcPO2 is unlikely to replace continuous intravascular measurement of PaO2 in infants with severe respiratory illnesses.