Normal range of fetal transcutaneous carbon dioxide tension during labour

Fetal transcutaneous carbon dioxide tension (tc-PCO2) was monitored during 122 deliveries, using an electrode temperature of 44 degrees C in 80 cases and of 41 degrees C in 42 cases. Significant correlations between tc-PCO2 and umbilical artery blood PCO2 were found using both electrode temperatures, but the regression lines indicated a larger and more inconstant CO2-contribution from skin metabolism when the low electrode temperature was used. Normal range of tc-PCO2 was calculated at 41 degrees C and 44 degrees C electrode temperatures. Mean values of fetal tc-PCO2 were found to increase during normal labour, and especially in fetuses developing acidosis, but only four of six infants born with acidaemia had tc-PCO2 values exceeding the normal range.     

Normal range of fetal transcutaneous carbon dioxide tension during labour

Summary. Fetal transcutaneous carbon dioxide tension (tc-Pco), was monitored during 122 deliveries, using an electrode temperature of 44°C in 80 cases and of 41°C in 42 cases. Significant correlations between tc- P co₂ and umbilical artery blood P co₂ were found using both electrode temperatures, but the regression lines indicated a larger and more inconstant CO₂-contribution from skin metabolism when the low electrode temperature was used. Normal range of tc- P co₂ was calculated at 41°C and 44°C electrode temperatures. Mean values of fetal tc- P co₂ were found to increase during normal labour, and especially in fetuses developing acidosis, but only four of six infants born with acidaemia had tc- P co₂ values exceeding the normal range.     

Continuous fetal intrapartum monitoring in supraventricular tachycardia by atraumatic measurement of transcutaneous carbon dioxide tension

A case of premature beats and paroxysmal supraventricular tachycardia without resulting congestive heart failure was diagnosed in a fetus of 38 weeks of gestation by echocardiography. Transplacental antiarrhythmic therapy was initiated, but a complete cardioversion was not achieved. Due to these arrhythmias adequate fetal heart rate monitoring during labor was not possible. By using continuous transcutaneous measurement of fetal carbon dioxide tension the fetus was delivered spontaneously, having been adequately monitored in spite of the effect on the fetal heart rate of the arrhythmias.     

Effects of maternal oxygen administration on fetal oxygenation during reductions in umbilical blood flow in fetal lambs

In 11 chronically catheterized fetal lambs (123 +/- 6, mean +/- SD, days of gestation; term = 147 days), we measured fetal oxygen delivery and oxygen consumption before and during reductions in umbilical blood flow (Qumb). Qumb was reduced by inflation of a balloon occluder located just proximal to the origin of the common umbilical artery. Measurements were made while the unanesthetized maternal sheep received either room air or 100% oxygen to breathe. In oxygen-treated fetuses, oxygen concentrations in umbilical venous blood (Cuvo2) and arterial blood (Cao2) were increased over a wide range of Qumb when compared with those of room air-treated fetuses. Because of these responses, fetal oxygen delivery (Do2 = Qumb X Cuvo2) and oxygen consumption [Vo2 = Qumb(Cuvo2-Cao2)] were greater in oxygen-treated fetuses than in room air-treated fetuses during episodes of reduced Qumb. In oxygen-treated fetuses, Vo2 decreased from normal levels only when Qumb was less than or equal to 75 ml/min/kg of fetus, whereas in room air-treated fetuses Vo2 decreased at Qumb less than or equal to 150 ml/min/kg. Our data indicate that oxygen administration to the pregnant sheep increases oxygen delivery to the fetus during times of reduced umbilical perfusion and that this supplemental oxygen supply provides an oxygen reserve with which the fetus can maintain oxidative metabolism. These data may be relevant to those clinical conditions, such as umbilical cord compression in labor, that are associated with reductions in umbilical blood flow.     

Effect of maternal carbon dioxide inhalation on human fetal breathing movements in term and preterm labor

Induced maternal hypercapnia is a potent stimulus to fetal breathing movements in nonlaboring pregnant women. To determine the effect of maternal CO2 administration on fetal breathing movements during spontaneous labor, 14 healthy pregnant volunteers at term and 34 in preterm labor were recruited. If fetal breathing movements were markedly decreased or absent, the subjects were administered a prepared gas mixture of 3% CO2 in air. In term labor and in true preterm labor, fetal breathing movements were markedly decreased and could not be induced by maternal hypercapnia. Among women with suspected preterm labor, initial absence of fetal breathing movements and failure to evoke this response by maternal hypercapnia predicted delivery within 48 hours with a sensitivity of 80% and specificity of 95.5%. Induced maternal hypercapnia fails to stimulate fetal breathing movements in true term and preterm labor and may assist in distinguishing between true and false preterm labor.     

Continuous, noninvasive measurement of fetal oxygen and carbon dioxide levels in labor by use of mass spectrometry

Clinical evaluation of the continuous, simultaneous measurement of fetal scalp surface oxygen and carbon dioxide partial pressures by mass spectrometry was undertaken for 52 labors. The mass spectrometer (MM8-80, V.G. Gas Analysis, Winsford, England) was easy to operate and had good long-term stability. The mean drifts for both oxygen and carbon dioxide over the study periods were less than 2 mm Hg. The mean (+/- SD) cervical dilatation at the time of transducer application was 6.1 (+/- 1.9) cm and the mean (+/- SD) duration of the studies was 169 (+/- 122) minutes; 10.5% of the transducer applications were unsuccessful. Falls in fetal scalp surface oxygen levels and rises in carbon dioxide levels were more frequent with late than with variable and with variable than with early fetal heart rate decelerations and with increasing severity and frequency of decelerations. Fetal scalp surface pressure changes also occurred with fetal heart rate variability changes, including some related to behavioral state changes. There was not a constant reciprocal relationship between oxygen and carbon dioxide changes, and fetal heart rate patterns were not related to actual blood gas levels. Fetal scalp surface measurements were related to both fetal blood sample and umbilical artery results. Trends in both oxygen and carbon dioxide levels during the course of labor were compared and related to other fetal variables, and most of the time the scalp surface measurements were an accurate guide to systemic blood gas levels. Maternal oxygen administration resulted in significant increase in fetal scalp surface oxygen levels, and on two of eight occasions it also led to decreases in fetal carbon dioxide levels. Scalp surface gas measurement by means of mass spectrometry is a powerful new method of intrapartum fetal monitoring, which should increase the precision of fetal surveillance as well as allow the accurate assessment of both established and new methods for optimizing labor and delivery.     

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.     

Tampon-induced changes in vaginal oxygen and carbon dioxide tensions

Vaginal oxygen and carbon dioxide tensions were measured continuously in a group of normal young women on the second day of menstruation during a 90-minute period. PO2 averaged 3 mm Hg (+/- 11 SD) and PCO2 averaged 64 mm Hg (+/- 13 SD). The value rose to that of atmospheric air when a tampon was inserted and gradually fell, giving a mean value of 112 mm Hg (+/- 18 SD) during the following 90 minutes; preinsertion values were reached in about 8 hours. Carbon dioxide rose rapidly to almost preinsertion values (mean value of 50 mm Hg +/- 12 SD) during the 90-minute period and remained steady at this level during extended periods. As in vitro studies have indicated an oxygen-dependent production of a toxin-like protein from Staphylococcus aureus, it is suggested that intravaginal tampons may be a risk factor in the development of toxic shock syndrome by supplying oxygen, thus changing the vaginal microenvironment from anaerobic to aerobic.     

Effect of prolonged asphyxia on skin blood flow in fetal lambs

Objective: To determine the effect of a prolonged period of asphyxia on skin blood flow, a potential indicator of fetal cardiovascular responses to asphyxia, in the chronically catheterized fetal lamb. Methods: Eight chronically instrumented pregnant ewes were studied at 118 +/- 1 days' gestation. After a control period, fetal acid-base status was assessed and regional blood flows were determined with dye-labeled microspheres. Fetal asphyxia was then induced by partial umbilical cord occlusion, decreasing fetal arterial oxygen pressure to 15 torr while maintaining pH above 7.28. Fetal cardiovascular status was monitored continuously. Fetal acid base status was evaluated every 10-15 minutes during cord occlusion. Regional blood flow determinations were repeated after 90 minutes of stable asphyxia. Results are expressed as the mean +/- standard error. Student t test for paired data was used to compare hemodynamic, acid-base, and regional blood flow determinations before cord occlusion and after 90 minutes of asphyxia.Results: There was a significant increase in blood flow to the fetal scalp from a control value of 52 +/- 8 mL per minutes per 100 g to 175 +/- 30 mL per minute per 100 g at 90 minutes of asphyxia (P =.01). Similarly, there was an increase in blood flow to the skin overlying the fetal hindquarter from 39 +/- 12 mL per minute per 100 g during control to 153 +/- 47 mL per minute per 100 g at asphyxia (P =.038). Conclusion: In the chronically instrumented fetal lamb, a 90-minute period of asphyxia produced by partial cord occlusion resulted in a significant increase in blood flow to the fetal skin.     

Fetal transcutaneous carbon dioxide tension during the second stage of labour

Summary. Fifteen women were studied during the second stage of labour by measuring simultaneously fetal transcutaneous carbon dioxide tension (Tc Pco₂ and maternal end-expiratory Pco₂ . A linear increase of Tc Pco₂ with time was observed, predominantly because of changing maternal respiration patterns. The degree of maternal hyperventilation had no adverse effect on the status of the newborn infant.     

Fetal transcutaneous carbon dioxide tension during the second stage of labour

Fifteen women were studied during the second stage of labour by measuring simultaneously fetal transcutaneous carbon dioxide tension (Tc PCO2 and maternal end-expiratory PCO2. A linear increase of Tc PCO2 with time was observed, predominantly because of changing maternal respiration patterns. The degree of maternal hyperventilation had no adverse effect on the status of the newborn infant.     

Effects of reductions in hemoglobin-oxygen affinity and hematocrit level on oxygen consumption and acid-base state in fetal lambs

To determine whether the high oxygen affinity of fetal blood, compared with that of the adult, is advantageous to the fetus during fetal anemia we studied 16 chronically catheterized fetal lambs. Half of the lambs had hemoglobin-oxygen affinity reduced acutely by isovolemic exchange transfusion with fresh adult whole blood; the other half served as controls. In both groups of fetuses, we measured fetal oxygen delivery, oxygen consumption, and acid-base state at normal fetal hematocrit levels and during reductions in the hematocrit level of 30% (moderate anemia) and 60% (severe anemia) produced by isovolemic exchange transfusions with plasma. At normal fetal hematocrit levels, reductions in hemoglobin-oxygen affinity had no effect on fetal oxygen consumption or acid-base state. During moderate anemia, fetal oxygen delivery decreased in both series of fetuses, but oxygen consumption and base excess fell only in those fetuses whose circulations contained adult hemoglobin. During severe anemia, oxygen consumption and base excess decreased in both groups of fetuses, although these changes were more pronounced in fetuses with adult hemoglobin than in those with fetal hemoglobin. Our data indicate that, even though a high hemoglobin-oxygen affinity may not be essential to a healthy fetus, it is critical for normal metabolism in a fetus subjected to a hypoxic stress such as anemia.     

Effects of position changes on transcutaneous carbon dioxide tension in neonates with respiratory distress

Routine neonatal care includes frequent position changes. Recent research has concluded that positions other than supine may result in beneficial physiologic responses. Specifically, several studies suggest that neonates may ventilate more effectively in a prone rather than in a supine position. This study tested the hypothesis that transcutaneous carbon dioxide tension (TcPCO2) would be lower in the prone than in the supine position in neonates with respiratory distress. Fourteen ventilated infants were studied. TcPCO2 was measured and recorded in prone, supine, and right-side-lying positions for each subject. There were no statistically significant differences in mean TcPCO2 values between the three positions (F = .45; df 2,39; P = .64). The relationship between TcPCO2 and PaCO2 values was stable (r = .88) during the studies. The results indicate that changing a neonate's position does not significantly alter transcutaneous carbon dioxide tension.     

The continuous measurement of transcutaneous carbon dioxide tension (TcPCO2), an atraumatic tool to verify fetal acidosis?

TcPCO2 monitoring of the fetus during labour was evaluated as an atraumatic tool to identify or exclude fetal acidosis in 224 high-risk deliveries. A heated electrochemical sensor with a measuring temperature of 39 degrees C (n = 105) or 44 degrees C (n = 119) was applied to the fetal scalp. There was a statistically significant correlation between the TcPCO2 and the fetal blood pH at both temperatures. The sensitivity of the method was 0.90 and 0.61 at the two measuring temperatures of 44 degrees or 39 degrees respectively and the specificity was 0.93 and 0.79 respectively. The negative predictive value was high (0.99 and 0.95 respectively), but the respective positive predictive values were only 0.53 and 0.24. We conclude that the continuous measurement of the TcPCO2 is a valid additional tool to exclude fetal acidosis in most cases where fetal distress is indicated by the heart rate pattern but a TcPCO2 value above the cut-off point should be verified by an additional method to avoid unnecessary operative deliveries.     

The continuous measurement of transcutaneous carbon dioxide tension (TcPCO2), an atraumatic tool to verify fetal acidosis?

Summary. Tc P CO₂ monitoring of the fetus during labour was evaluated as an atraumatic tool to identify or exclude fetal acidosis in 224 high-risk deliveries. A heated electrochemical sensor with a measuring temperature of 39°C ( n = 105) or 44°C( n =119) was applied to the fetal scalp. There was a statistically significant correlation between the Tc P CO₂ and the fetal blood pH at both temperatures. The sensitivity of the method was 0.90 and 0.61 at the two measuring temperatures of 44° or 39° respectively and the specificity was 0.93 and 0.79 respectively. The negative predictive value was high (0.99 and 0.95 respectively), but the respective positive predictive values were only 0.53 and 0.24. We conclude that the continuous measurement of the Tc P CO₂ is a valid additional tool to exclude fetal acidosis in most cases where fetal distress is indicated by the heart rate pattern but a Tc P CO₂ value above the cut-off point should be verified by an additional method to avoid unnecessary-operative deliveries.     

The role of carbon dioxide in the generation of human fetal breathing movements

To determine the role of carbon dioxide in the generation of fetal respiratory movements, the effect of induced maternal hypocapnia and hypercapnia on fetal breathing movements, gross body movements, and fetal heart rate was studied in 12 healthy pregnant women near term. Patients were studied for a 1-hour control period breathing room air followed by four randomized 15-minute study periods with patients breathing either room air, a prepared gas mixture with 2% or 4% carbon dioxide, or undergoing controlled hyperventilation as determined by monitoring end-tidal PCO2. The percentage of time fetal breathing movements correlated significantly with maternal end-tidal PCO2 (r = 0.62, p less than 0.01), increasing with maternal breathing of 2% and 4% carbon dioxide and decreasing with maternal hyperventilation. Fetal gross body movements, fetal heart rate, and fetal heart rate variability showed no significant changes. It is concluded that as in adults, the carbon dioxide level in fetuses is an important stimulus for the generation of respiratory movements, acting independent of a change in behavioral state. It is hypothesized that tonic carbon dioxide level input is an important determinant of fetal respiratory center drive, but little or no phasic carbon dioxide input exists because of continuous placental excretion, thus resulting in the episodic occurrence of breathing movements with changes in the fetal behavioral state.