Effect of maternal oxygenation on fetal blood gas status in shiba goat fetuses

The purpose of this study is to investigate the effect of maternal oxygen administration on the fetal blood gas status. Five Shiba goat fetuses were used whose gestational days were 134 +/- 4 days. Maternal and fetal pH, pO2, pCO2, B.E., and hematocrit were measured every 30 minutes during 4 l/min oxygen administration for 60 minutes. Maternal arterial blood pO2 increased from 95.5 +/- 19.6 mmHg to 262.6 +/- 75.8 mmHg at 30 minutes and to 207.8 +/- 110.1 mmHg at 60 minutes. Fetal arterial blood pO2 increased significantly from 18.4 +/- 3.0 mmHg to 24.4 +/- 5.8 mmHg and 23.6 +/- 6.9 mmHg, respectively. There was a significant positive correlation between maternal pO2 and fetal pO2. The increase in fetal pO2 was small when the control pO2 was less than 17 mmHg. Although maternal pH did not change significantly, fetal pH decreased significantly from 7.29 +/- 0.07 to 7.25 +/- 0.07 at 60 minutes. Also fetal hematocrit decreased significantly from 33.9 +/- 5.2% to 32.8 +/- 5.4% at 60 minutes. Neither maternal nor fetal pCO2 and B.E. changed significantly. Therefore, we concluded that the effect of maternal oxygen administration on fetal pO2 was small when the fetus was already hypoxic. Also 60 minutes' oxygen administration may cause the decrease in fetal pH and hemodilution.     

The effects of maternal exercise on fetal oxygenation and feto-placental growth

Sustained bouts of maternal exercise during pregnancy cause an acute reduction in oxygen and nutrient delivery to the placental site. The decreased flow also initiates a slight fall in intervillous and fetal pO2 which initiates a fetal sympathetic response. This, coupled with hemoconcentration and improved placental perfusion balance, maintains fetal tissue perfusion and oxygen uptake. Exercise training during pregnancy (regular bouts of sustained exercise) increases resting maternal (and perhaps fetal) plasma volume, intervillous space blood volume, cardiac output and placental function. These changes buffer the acute reductions in oxygen and nutrient delivery during exercise and probably increase 24 h nutrient delivery to the placental site. Thus, the effect of any given exercise regimen on fetal growth and size at birth is dependent on the type, frequency, intensity and duration of the exercise as well as the time point in the pregnancy when the exercise is performed. Maternal carbohydrate intake is yet another modifying factor. Beginning a moderate exercise regimen increases both anatomic markers of placental function and size at birth while maintaining a rigorous exercise regimen throughout pregnancy selectively reduces growth of the fetal fat organ and size at birth. Likewise, decreasing exercise performance in late-pregnancy increases size at birth while increasing exercise performance decreases it. Finally, the infants born of exercising women who eat carbohydrates which elevate 24 h blood glucose levels are large at birth irrespective of exercise performance.     

Intrapartum maternal glucose infusion and fetal acid-base status.

OBJECTIVE: To compare the effects of an intrapartum infusion of a lactated Ringer solution or a glucose-boosted saline solution on the acid-base status of umbilical arterial blood. METHOD: In a prospective clinical trial 178 women in labor were randomized to receive intravenously either a lactated Ringer solution or a saline solution boosted with 5% glucose. Umbilical arterial blood was then assessed for acid-base status. RESULTS: There were significant differences between the lactated Ringer group and the glucose group in umbilical artery pH values (7.25+/-0.07 vs. 7.28+/-0.06; P=0.008), pCO2 values (44.8+/-5.6 mm Hg vs. 41.6+/-4.1 mm Hg; P=0.001), and base excess (-7.3+/-2.1 mEq/L vs. -6.6+/-1.8 mEq/L; P=0.02). CONCLUSION: Intrapartum intravenous fluid containing a 5% glucose solution reduces umbilical cord acidemia and hypercarbia.     

The influence of maternal epidural analgesia upon intrapartum fetal oxygenation

Objective. The use of maternal epidural analgesia in labor may be associated with non-reassuring fetal heart rate (FHR) patterns. We aimed to assess changes in fetal oxygen saturation (FSpO₂) during epidural analgesia in labor.

Methods. This was a prospective observational study. Twenty healthy parturients were enrolled following the inclusion criteria. Informed consent was obtained. Mode of delivery, use of oxytocin, maternal blood pressure, umbilical cord blood analysis, Apgar score, and neonatal outcomes were evaluated. Ropivacaine at a low concentration of 0.1% (1 mg/mL) co-administered with an opioid (fentanyl 2.5 µg/mL) was used. The values of fetal oxygen saturation were registered continuously 10 minutes before the administration of the analgesic drug and during the following 30 minutes after administration. Pulse oximetry was used simultaneously with cardiotocography (CTG).

Results. The average value for fetal oxygen saturation before the analgesic drug administration was 44.3 ± 8.8%; during the first 10 minutes following administration it was 41.3 ± 7.2% (p = 0.25) and during the following 20 minutes it was 43.05% ± 6.9% (p = 0.63). There was no direct relationship between non-reassuring CTG pattern appearance and FSpO₂ <30% (RR = 1.11, 95% CI 0.76–1.64). No significant correlation was found between FSpO₂ values within the first 30 minutes of epidural analgesia and neonatal acidotic status (pH ≤7.00; RR = 0.33, 95% CI 0.04–3.09, and base excess ≤?12 mmol/L; RR = 1, 95% CI 0.21–4.71).

Conclusions. There were no differences in FSpO₂ values in the first 30 minutes following administration of analgesic drugs and most of the cases with non-reassuring CTG patterns had values of FSpO₂ constantly ≥30%.     

Does fetal acidosis develop with maternal glucose infusion during normal labor?

The actual effects of glucose infusion on fetal acid-base status were studied during 125 normal deliveries in which plasma glucose and acid-base parameters were determined after maternal infusion of either 10% glucose or Ringer's solution. After 80 minutes, mean (+/- SD) plasma glucose levels were significantly higher in the glucose group (N = 59) than in the Ringer's group (N = 66), both for the mother (183.6 +/- 46.8 versus 95.3 +/- 18.0 mg/dL) and the fetus (108.4 +/- 41.4 versus 64.8 +/- 16.2 mg/dL). Fetal plasma lactate concentrations did not differ between the glucose and the Ringer's groups, but were significantly lower in the fetuses delivered by elective cesarean section in both groups. With glucose administration, fetal pCO2 was higher and pH values were lower than in the Ringer's group. However, the magnitude of acid-base status changes, indicated by both pH and pCO2 shifts (ie, the difference between umbilical artery and scalp values), failed to differ between the two groups. In fetuses with progressing hypoxia, no differences in any of the acid-base parameters were observed between glucose and Ringer's administration. These data indicate that at a glucose infusion rate of 30 g/hour, fetal acidosis, when it occurs, results from hypoxia rather than from maternal glucose administration.     

The influence of maternal epidural analgesia upon intrapartum fetal oxygenation.

OBJECTIVE: The use of maternal epidural analgesia in labor may be associated with non-reassuring fetal heart rate (FHR) patterns. We aimed to assess changes in fetal oxygen saturation (FSpO(2)) during epidural analgesia in labor. METHODS: This was a prospective observational study. Twenty healthy parturients were enrolled following the inclusion criteria. Informed consent was obtained. Mode of delivery, use of oxytocin, maternal blood pressure, umbilical cord blood analysis, Apgar score, and neonatal outcomes were evaluated. Ropivacaine at a low concentration of 0.1% (1 mg/mL) co-administered with an opioid (fentanyl 2.5 microg/mL) was used. The values of fetal oxygen saturation were registered continuously 10 minutes before the administration of the analgesic drug and during the following 30 minutes after administration. Pulse oximetry was used simultaneously with cardiotocography (CTG). RESULTS: The average value for fetal oxygen saturation before the analgesic drug administration was 44.3 +/- 8.8%; during the first 10 minutes following administration it was 41.3 +/- 7.2% (p = 0.25) and during the following 20 minutes it was 43.05% +/- 6.9% (p = 0.63). There was no direct relationship between non-reassuring CTG pattern appearance and FSpO(2) <30% (RR = 1.11, 95% CI 0.76-1.64). No significant correlation was found between FSpO(2) values within the first 30 minutes of epidural analgesia and neonatal acidotic status (pH or=30%.     

Acute effects of maternal ethanol infusion on fetal cardiac performance

In adult animals and man, both acute and chronic ethanol intake is associated with depression of myocardial performance. Accordingly, the cardiac effects of maternal ethanol infusions, in a manner comparable to common obstetric practice for inhibition of premature labor, were evaluated in six chronically instrumented fetal sheep. Fetal and ewe arterial Po₂, Pco₂, and pH values remained within normal limits with infusion rates of 15 c.c. per kilogram of 10 per cent ethanol over two hours (blood ethanol = 110 mg. per cent) and 15 c.c. per kilogram over one hour (blood ethanol = 210 mg. per cent). Fetal instrument evaluation (for 14 to 30 days after operation) provided data concerning pressures and cardiac dimensions which allowed analysis of left ventricular performance. Ethanol produced a significant depression of the extent (p < 0.01) and velocity (p < 0.001) of left ventricular myocardial fiber shortening as well as in the mean rate of left ventricular circumferential fiber shortening (p < 0.01). These indices of cardiac contractility were depressed in the absence of changes in end diastolic diameter, left atrial pressure, and systemic arterial pressure. Thus, the practice of inhibition of premature labor with ethanol might contribute to depressed myocardial performance in the neonatal period.     

The effect of acute maternal hypoxia on fetal oxygenation and the umbilical circulation in the sheep

The mean oxygen consumption was 8.4 ± 1.9 ml/min/kg in the near-term fetal sheep. In response to acute maternal hypoxia fetal O₂ consumption decreased to lower than 50% of the control values. The decrease was rapidly instituted, proportional to the degree of hypoxia, sustained for up to 47 min and stable over this period. With increasing duration of hypoxia, a progressive metabolic acidosis developed. Recovery of oxygen consumption occurred rapidly after hypoxia ceased, though the acidosis was not resolved until 2 h later. Umbilical blood flow was maintained during maternal hypoxia and umbilical arterial and venous pressures increased. A fetal bradycardia invariably accompanied the hypoxia.     

Decreased urine production in the near-term fetal lamb after maternal ethanol infusion

Intravenous infusion of 1 gm ethanol/kg maternal body weight over 1 hour to three conscious catheterized near-term pregnant ewes decreased fetal urine production for 3 hours (overall decrease of 54% from control). This effect in the near-term fetus is opposite to the ethanol-induced diuresis that occurs in adults.     

The effects of xylazine on uterine activity, fetal and maternal oxygenation, cardiovascular function, and fetal breathing

Various pharmacologic agents used in the experimental study of physiologic processes may have pronounced effects on the systems under study. We have studied the effects of xylazine (Rompun) on myometrial activity, fetal and maternal pH, blood gases, heart rate, and fetal breathing movements in chronically catheterized fetal sheep. Xylazine is widely used as a premedication for various forms of animal operations, including the instrumentation of the chronically catheterized fetal sheep preparation. Animals were studied on postoperative day 5. Xylazine had pronounced effects on maternal PaO2 and heart rate that lasted for at least 3 hours. Fetal heart rate and PaO2 returned to preinjection levels within 60 minutes. Myometrial activity doubled in the first 60 minutes after administration of xylazine and did not return to preinjection levels for 3 hours. Fetal diaphragmatic electromyographic activity was almost completely absent in the first and second hours, with a return to normal within 4 hours. These changes were absent in the saline solution-injected control animals. The observed changes in uterine activity and fetal breathing may have been direct effects of xylazine itself or the result of increased uterine activity. The different duration of changes in the ewe and fetus suggests a compensatory mechanism at the uteroplacental level or in the fetoplacental unit.     

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.     

The effect of labour and maternal oxytocin infusion on fetal plasma oxytocin concentration

It is not known whether human labour is associated with increased fetal oxytocin production or transfer of oxytocin across the placenta. Previous reports are contradictory, due in part, to the influence of maternal analgesia on fetal production. We determined plasma oxytocin concentration in the umbilical artery and vein of women after vaginal delivery and after caesarean section with general anaesthesia before or after the onset of labour. The results demonstrate that fetal production of oxytocin is not influenced by general anaesthesia, thus enabling comparison of labour and nonlabour samples at caesarean section. Labour was not associated with an increase in fetal oxytocin production. Oxytocin was also measured in the umbilical artery and vein during maternal oxytocin infusion to assess placental transfer. The results do not support transfer of oxytocin across the placenta in women.     

The effect of labour and maternal oxytocin infusion on fetal plasma oxytocin concentration

It is not known whether human labour is associated with increased fetal oxytocin production or transfer of oxytocin across the placenta. Previous reports are contradictory, due in part, to the influence of maternal analgesia on fetal production. We determined plasma oxytocin concentration in the umbilical artery and vein of women after vaginal delivery and after caesarean section with general anaesthesia before or after the onset of labour. The results demonstrate that fetal production of oxytocin is not influenced by general anaesthesia, thus enabling comparison of labour and nonlabour samples at caesarean section. Labour was not associated with an increase in fetal oxytocin production. Oxytocin was also measured in the umbilical artery and vein during maternal oxytocin infusion to assess placental transfer. The results do not support transfer of oxytocin across the placenta in women.     

Effects of maternal ethanol infusion on fetal cardiovascular and brain activity in lambs

Ethanol (1 gm/kg of maternal body weight administered over 1 hour) was infused intravenously into 11 chronically prepared pregnant ewes between 128 to 137 days' gestation. Fetal breathing movements were suppressed for 9 hours following ethanol administration, and both high- and low-voltage fetal electrocortical activity were suppressed for 3 hours and replaced by intermediate-voltage electrocortical activity. Fetal blood gases and pH were not altered. These data support the hypothesis that ethanol suppresses fetal breathing movements by a direct central mechanism rather than indirectly by alteration of electrocortical activity.