Measurement and processing of fetal transcutaneous Pco2levels

Publisher Website
Google Scholar
Abstract
Because asphyxia is not the only factor influencing fetal heart rhythm, a non-optimal cardiotachogram is not necessarily a sign of fetal distress. It makes further evaluation of the fetal condition advisable, especially determination of the acid-base equilibrium. The method of fetal blood sampling, introduced by SALING, has a number of disadvantages for mother and fetus, because of the invasiveness for both. Further, the measured acid-base equilibrium in only representative for a very short period of time and often repreated microblood sampling is necessary. A major problem with regard to determination of the acid-base equilibrium in intermittently obtained fetal blood samples is the inclusion of air bubbles in the sample. When they are introduced into the electrode cuvettes, the measured values cannot be considered reliable. The problem was solved in the Department of Obstetrics and Gynecology of the Vrije Universiteit of Amsterdam with a "pipe" shaped special collecting vessel. Similar measuring results were obtained with the formerly used glass capillary method and the special collecting vessel method. Continuous, non-invasive methods have been pursued to avoid the above mentioned problems. Fetal transcutaneous PO2 measurement has been possible for years, but does not provide adequate information during the important second stage of labor because of methodological problems. Continuous fetal tissue pH surveillance is possible, but it also has an invasive character and is technically difficult to perform, leading to many methodological failures. Recently, continuous transcutaneous PCO2 measurement tcPCO2 became available. A good correlation was found with simultaneously measured PCO2 levels in fetal blood samples and with those of umbilical artery blood. Presently, available literature indicates that acute deterioration of the fetal condition during labor was always preceded by a raise of fetal tcPCO2. Therefore, fetal tcPCO2 surveillance potentially is a valuable adjunct to monitor the fetal condition, if reliable and adequate assessment can be obtained. The method will be evaluated in a multicenter study of the working group "New Methods" of the European Community project "Perinatal Monitoring". In our department we are comparing the predictive value of fetal tcPCO2 measurement with that of the cardiotachogram. Besides, we are studying the influence of maternal tcPCO2 on fetal tcPCO2 levels. To reach our aim we need to record: fetal heart rate, maternal uterine activity, fetal tcPCO2, heat consumption of the fetal tcPCO2 electrode, maternal tcPCO2 heat consumption of the maternal tcPCO2 electrode and events during labor. Computerization of these data is desirable and has the following advantages: synchronisation of signals, no limitation of the number of signals that can be recorded, data reduction, orderly and variable display, quantitative analysis. Our technical service center developed a system in which the data are collected by a digital VT 103 datalogger and then transmitted to a P. D. P. 11/34 computer for further processing and evaluation.