Measurement and processing of fetal transcutaneous Pco2 levels

Summary Because asphyxia is not the only factor influencing fetalheart rhythm, a non-optimal cardiotachogram is notnecessarily a sign of fetal distress. It makes furtherevaluation of the fetal condition advisable, especiallydetermination of the acid-base equilibrium.The method of fetal blood sampling, introduced bySALING, has a number of disadvantages for mother andfetus, because of the invasiveness for both. Further, themeasured acid-base equilibrium is only representativefor a very short period of time and often repeated micro-blood sampling is necessary.A major problem with regard to determination of theacid-base equilibrium in intermittently obtained fetalblood samples is the inclusion of air bubbles in thesample. When they are introduced into the electrodecuvettes, the measured values cannot be considered reli-able. The problem was solved in the Department ofObstetrics and Gynecology of the Vrije Universiteit ofAmsterdam with a "pipe"shaped special collecting ves-sel. Similar measuring results were obtained with theformerly used glass capillary method and the specialcollecting vessel method.Continuous, non-invasive methods have been pursuedto avoid the above mentioned problems. Fetal transcu-taneous Ρθ2 measurement has been possible for years,but does not provide adequate information during theimportant second stage of labor because of methodologi-cal problems.Continuous fetal tissue pH surveillance is possible, butit also has an invasive character and is technically diffi-cult to perform, leading to many methodological failu-res.Recently, continuous transcutaneous Pco2 measurementtcPco2 became available. A good correlation was foundwith simultaneously measured Pco2 levels in fetal bloodsamples and with those of umbilical artery blood.Presently, available literature indicates that acute de-terioration of the fetal condition during labor was al-ways preceded by a raise of fetal tcPco2. Therefore, fetaltcPco2 surveillance potentially is a valuable adjunct tomonitor the fetal condition, if reliable and adequateassessment can be obtained. The method will be evalu-ated in a multicenter study of the working group "NewMethods" of the European Community project "Perin-atal Monitoring".In our department we ar comparing the predictive valueof fetal tcPco2 measurement with that of the cardiota-chogram. Besides, we are studying the influence of ma-ternal tcPco2 on fetal tcPco2 levels. To reach our aim weneed to record: fetal heart rate, maternal uterine activity,fetal tcPco2, heat consumption of the fetal tcPco2 elec-trode, maternal tcPco2, heat consumption of the ma-ternal tcPco2 electrode and events during labor. Com-puterization of these data is desirable and has followingadvantages:— synchronisation of signals,— no limitation of the number of signals that can berecorded,— data reduction,— orderly and variable display,— quantitative analysis.Our technical service center developed a system in whichthe data are collected by a digital VT103 dataloggerand then transmitted to a P. D. P. 11/34 computer forfurther processing and evaluation.