Reliability of transcutaneous measurement of oxygen and carbon dioxide partial pressure with a combined Po2-Pco2 electrochemical sensor in the fetus during labor.

A combined single electrochemical sensor designed to measure synchronously and transcutaneously oxygen partial pressure and carbon dioxide partial pressure (RADIOMETER prototype) was applied onto the scalp in 21 fetuses during labor. The values of tcPo2 respectively tcPco2 were compared with the values of fetal blood analysis (FBA) and blood from the umbilical artery (UA): Comparing the tcPco2 with the values of the FBA we found the values to be very consistent (r = 0.95, p less than 0.001). For the comparison of the tcPco2 with the values of the umbilical artery, the correlation coefficient was lower (r = 0.76, p less than 0.05). The transcutaneous measurement of Po2 as compared with the values of the fetal blood analysis was also quite accurate (r = 0.83, p less than 0.001). Looking at the values of the transcutaneous measurement during the expulsion of the fetus and its comparison with the values of the umbilical artery, it was an interesting finding that values of the transcutaneous estimation of Po2 were much lower in some cases and no statistical correlation was found (p greater than 0.05). We conclude that the combined electrochemical sensor for measuring tcPco2 and tcPo2 is a new additional tool for studying the physiology and pathophysiology of the fetus during labor, but as the accuracy of Po2 and Pco2 in the fetal blood is influenced by the progress of labor, the special characteristic of the transcutaneous measurement has to be taken into account when values are interpreted.