TRANSCUTANEOUS PCO2 DURING LABOR - A COMPARISON WITH FETAL BLOOD-GAS ANALYSIS AND TRANSCUTANEOUS PO2

Reduction of lethal and compromised fetal outcome is a benefit of rising socio-economic standards and better health care, including technologies such as cardiotocography and fetal blood analysis. The pursuit of higher standards in obstetrics leads to new and improved techniques. The transcutaneously measured carbon dioxide tension (tc PCO2) was proposed as a continuous and non-invasive method revealing the acid-base status of the fetus. Nonetheless, intrapartum surveillance by measuring tc PCO2 is rarely used in clinical practice. To assess the value of fetal monitoring by tc PCO2 during parturition, tc PCO2 measurements were compared with the fetal acid-base status. Tc PCO2 was measured by a recently developed electrode during 21 deliveries. The tc PCO2 electrode was disinfected, calibrated and applied to the presenting part of the fetus after rupture of membranes. The acid-base status of the fetus was determined with a commercial blood gas analyser in capillary blood (n = 33) and umbilical artery samples (n = 15). Tc PCO2 was correlated with the PCO2 of the capillary blood (r = 0.56; n = 33; P < 0.001) as well as with the PCO2 in the umbilical artery (r = 0.75; n = 15; P < 0.01). The pH value of capillary blood was related to tc PCO2 (r = -0.56; n = 33; P < 0.001). However, tc PCO2 did not show a significant relation with the pH value in the umbilical artery (r = -0.34; n = 15). Variations in skin blood flow are known to decrease the transcutaneously measured oxygen tension (tc PO2) below the PO2 in the capillary and umbilical blood. The simultaneously measured tc PCO2 approximately equalled the capillary and umbilical PCO2. Hence, tc PCO2 is rather independent of skin blood flow during uncomplicated deliveries. We conclude, that non-invasive and continuous measurement of fetal tc PCO2 provides information about the acid-base status of the fetus. Tc PCO2 cannot replace fetal blood analysis, though it may reduce the need for repeated fetal blood analysis during deliveries if signs of fetal distress occur.