The influence of the progress of labor on the reliability of the transcutaneous P_CO2of the fetus

Abstract

Transcutaneous PCO2 measurements were performed on 105 fetuses during labor. A modified Severinghaus electrode was calibrated with 5% and 10% carbon-dioxide gas at 33 and 66torr. This corresponds to a drop in the PCO2 levels measured transcutaneously of about 13% and to an adjustment to the blood gas level. The levels measured transcutaneously were compared with data compiled from the fetal blood analysis and values of blood gas analysis from the umbilical artery immediately after delivery. The object of the study was to find out to what extent the progress of labor influences the conformity between the PCO2 levels measured transcutaneously and measured in blood. Comparing the data of the transcutaneous measurement (pb PCO2) with the pb PCO2 of the peripheral blood (pb PCO2) in cases without a caput succedaneum, we found a correlation coefficient of r = 0.79 and a slope of 1.1. On the other hand with the development of a caput succedaneum the correlation coefficient was lowered to r = 0.72 and the slope to 0.85. An influence of the propulsion of the fetal head in the birth canal on the accuracy of the transcutaneous measurement was also obvious. When the position of the fetal head was either above or in the interspinal plane, the correlation coefficient amounted to r = 0.85. With the progression below the interspinal plane, the correlation coefficient was clearly lowered. While our results show a good overall conformity between PCO2 levels measured transcutaneously and those from peripheral blood, our analysis shows also to what extent the conformity can be influenced both by the existence of a caput succedaneum and by the propulsion of the presenting part.

Transcutaneous carbon dioxide measurements in the fetus during labor

“…However, the correlation between second stage values and umbilical artery values was only slightly improved. This lack of correlation to umbilical artery measurements is in disagreement with the results of others [2,6,7,8]. This discrepancy might be caused by the small number of cases, in which tcPco2 was measured until just before delivery and correlated to umbilical artery Pco2 (n = 9).…”

“…Additionally, the absence of high values in our series (62 mmHg maximum) tends to lower the correlation coefficient. Our only technical problem was that the stabilization time was greater than that of others (average 27 minutes in our series versus 18 minutes [7]). In addition to our lack of training in a new technique, two technical components might explain these differences.…”

“…The interest focused then on the use of a transcutaneous Pco2 for fetal monitoring. This technique was mostly used by two teams in Berlin [6,7] and Copenhagen [2], which carried out an experimental study and demonstrated its reliability. The results obtained were so stimulating that an evaluation of the practicability of this electrode in an enlarged scale by teams less well aware of technical problems could be envisaged.…”

Evaluation of the discrepancy between pH and lactate in combined fetal scalp blood sampling

“…Factors other than hypoxia, such as contamination of amniotic fluid during sampling, might increase fetal lactate levels (13,14). If local perfusion is limited (such as with caput formation) then scalp lactate levels can increase without an underlying fetal compromise (9,15). Furthermore, the fetal acid‐base balance is influenced by maternal hyperventilation, catecholamine concentrations, and the administration of beta‐mimetic drugs or glucose (16).…”

Non-invasive continuous fetal transcutaneous pO 2 and pCO 2 monitoring during labor

“…O'CONNER et al [14] have named this phenomenon the "tonsure effect". Moreover, with development of a caput succedaneum, correlation coefficients between the transcutaneous blood were lowered for tcpO 2 (L FGREN, 1977) [9] and tcpCO 2 (SCHMIDT and SALING, 1985) [19], and as a result unreliable recordings were given. Our technique of applying the electrode with a vacuum gave 76% successful recordings, as good a result as in WEBER'S reports [26].…”