K. Langner

Correlation between transcutaneous pCO2 and the corresponding values of fetal blood — a study at a measuring temperature of 39 °C

Continuous transcutaneous monitoring of fetal carbon dioxide partial pressure (tcpCO2) may become an important new method for investigating the physiology and pathophysiology of the fetus during labor, as well as an additional tool for fetal surveillance. In order to contribute to the standardization of this newly developed method, we measured tcpCO2 during labor in 105 fetuses. We then compared the transcutaneous pCO2 with the pCO2 of fetal blood gas analysis; the correlation between these two parameters was significant. The relationship between transcutaneous pCO2 and the pH from fetal scalp blood is described, as is the influence of the stage of labor on the correlation between transcutaneous monitoring and blood samples. tcpCO2 during labor appears to be a helpful additional tool, especially in fetuses with pathologic heart rate patterns in whom multiple fetal blood gas analysis would otherwise be necessary.

The influence of the progress of labor on the reliability of the transcutaneous PCO2 of the fetus.

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.

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.

The influence of oxygen administration to the mother during labor on the fetal transcutaneously measured carbon-dioxide partial pressure.

The aim of this study was to plot the course of the transcutaneously measured PCO2 (tcPCO2) in the fetus during oxygenation of the mother. In our examination 35 parturients with a suspicious or pathologic CTG were given pure oxygen for 10 minutes at a flow speed of 10 l/min. The fetal tcPCO2 was measured with a TCM 3 measuring device from Radiometer. The measuring temperature was 41 degrees C. The fetal tcPCO2 was 67.2 +/- 3.9 mmHg before the O2 application, during the O2 application it was 67.3 +/- 14.1 mmHg and for the period after the O2 application we found an average measurement of 66.7 +/- 13.9 mmHg. Further we investigated whether, depending on the original levels of the fetal tcPCO2 an O2 application to the mother had a measurable effect on the fetal tcPCO2 levels. The average levels of the tcPCO2 in the fetuses with pathological original levels of greater than or equal to 60 mmHg or with normal levels of less than 60 mmHg did not show any significant differences before, during or after the O2 application. Our own results and reports given in the literature about an increase in the fetal O2 partial pressure during maternal oxygenation lead to the conclusion that in cases with fetal hypoxia, the O2 application to the mother--in addition to other measures for intrauterine reanimation or speedy termination of labor--could be of advantage.

Effect of continuous lumbar epidural anaesthesia during labour on fetal transcutaneous carbon dioxide.

The effect of epidural anaesthesia during labour on fetal transcutaneous carbon dioxide (tcPCO2) was observed on 27 fetuses. Our results show that in the course of epidural anaesthesia there is an increase in fetal tcPCO2. We can see a slight increase even before administering the test dose, while preparatory measures are undertaken for the epidural anaesthesia. After administering the test dose and after giving the main dose there is a further increase in fetal tcPCO2, which continues for up to 30 min after the main dose has been given. The results suggest that it is important to consider any pathological conditions in the fetus, so as to avoid the possibility of additionally endangering the fetus during epidural anaesthesia.

In-vivo NMR spectroscopy of the fetal lung in guinea-pigs.

We have been successful in achieving phosphorus NMR in-vivo spectra of the fetal lung in an animal model. We used pregnant guinea-pigs with a gestational age of 45 to 65 days. The spectra were recorded on a Bruker tomograph (BMT 24/30) with a field strength of 2.35 T. The spectra showed a typical pattern. After recording the animals were sacrificed and the lungs were prepared for electron microscopic examinations. In the spectra peaks were found which appeared to be phosphorylcholine and phosphatidylcholine. For one peak it could be observed that the relative signal intensity increased with increasing gestational age as well as with increasing lung maturity. This could not be observed for other peaks. So the lecithin of the surfactant in the tissue of the fetal lung appears to be directly accessible through phosphorus in-vivo NMR spectroscopy. The peaks found appear already before the lamellar bodies are present in the pneumocytes type II.

Glycosylated hemoglobin (HbA1), glucose tolerance and neonatal outcome in gestational diabetic and non-diabetic mothers

Glycosylated hemoglobin (HbA1) was determined in three subject groups: 69 non-diabetic mothers who were delivered of normal weight infants at term (Group I), 33 non-diabetic mothers who were delivered of macrosomic infants (greater than 4000 g) at term (Group II), 51 gestational diabetics in the 3rd trimester--before onset of the diabetes therapy (Group III). In all three groups diagnostic assessment of glucose regulation was done by means of the oral glucose tolerance test during the 3rd trimester. Glycosylated hemoglobin was assayed by cation-exchange chromatography in small disposable columns. The mean values and standard deviations of HbA1 were 6.51 +/- 0.46% in Group I, 6.59 +/- 0.42% in Group II and 7.11 +/- 0.56% in Group III. Between the HbA1 values of Group III (gestational diabetes) on the one hand and those of the non-diabetic groups I and II on the other, there were highly significant differences (p less than 0.001; x2-test). HbA1 values above 7.4%--i.e. above mean + 2 s. d. of HbA1 in the non-diabetic mothers--were with 95% probability abnormal and indicative of gestational diabetes. HbA1 values between 7.0% and 7.4% were suspected of impaired glucose tolerance and gestational diabetes respectively. Between the HbA1 levels in the non-diabetic groups and those in the gestational diabetic group there was a vast zone with overlapping values. HbA1 data situated in this transitional area could be found both in non-diabetic subjects and also in those with abnormal glucose regulation. HbA1 values below 6.0% excluded gestational diabetes or otherwise impaired glucose tolerance with a high degree of probability.