Fetal Acid-base Status Research Articles

Relationship Between Combined Fetal Biophysical Activities, Oligohydramnios, and Fetal Acid–Base Status

The purpose of this study was to determine the relationship between combined fetal biophysical activities, oligohydramnios, and fetal acid-base status at the time of testing. In a prospective study of 101 patients undergoing cesarean section before the onset of labor, a fetal biophysical profile was performed within 3 h before the cesarean section. Different combinations of fetal biophysical activities (fetal heart rate reactivity, fetal breathing movements, fetal body movements, and fetal tone) and oligohydramnios were correlated with umbilical cord blood gas and acid-base measurements (artery and vein). Fetal acidemia was defined as umbilical arterial blood pH <7.20. The group of fetuses with reactive nonstress test (NST) and/or fetal breathing present had significantly higher pH, pO2, bicarbonate, and base excess and significantly lower pCO2 levels compared with fetuses who had nonreactive NST, absent fetal breathing, and compromised or absent body movements and tone. These blood gas and acid-base diff...

Transcutaneous P co 2 during labor — a comparison with fetal blood gas analysis and transcutaneous P o 2

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 P co 2 ) was proposed as a continuous and non-invasive method revealing the acid-base status of the fetus. Nonetheless, intrapartum surveillance by measuring tc P co 2 is rarely used in clinical practice. To assess the value of fetal monitoring by tc P co 2 during parturition, tc P co 2 measurements were compared with the fetal acid-base status. Tc P co 2 was measured by a recently developed electrode during 21 deliveries. The tc P co 2 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 P co 2 was correlated with the P co 2 of the capillary blood ( r = 0.56; n = 33; P < 0.001) as well as with the P co 2 in the umbilical artery ( r = 0.75; n = 15; P < 0.01). The pH value of capillary blood was related to tc P co 2 ( r = − 0.56; n = 33; P < 0.001). However, tc P co 2 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 P o 2 ) below the P o 2 in the capillary and umbilical blood. The simultaneously measured tc P co 2 approximately equalled the capillary and umbilical P co 2 . Hence, tc P co 2 is rather independent of skin blood flow during uncomplicated deliveries. We conclude, that non-invasive and continuous measurement of fetal tc P co 2 provides information about the acid-base status of the fetus. Tc P co 2 cannot replace fetal blood analysis, though it may reduce the need for repeated fetal blood analysis during deliveries if signs of fetal distress occur.

The effect of nicardipine on maternal and fetal hemodynamics and uterine blood flow in chronically instrumented pregnant goats.

This study was designed to clarify the maternal and fetal hemodynamics of nicardipine (0.02 mg/kg) administered intravenously to unanesthetized, chronically instrumented pregnant goats. Nicardipine produced a significant increase in maternal heart rate and cardiac output, and a significant decrease in maternal mean arterial blood pressure and systemic vascular resistance. These changes persisted for about 30 minutes. There were no consistent changes in maternal pulmonary hemodynamics. Uterine arterial blood flow (UBF) decreased significantly (about 15%) after 5 minutes of the injection and returned to the control value within 30 minutes. A significant correlation between the decreases in UBF and maternal diastolic blood pressure was observed after 5 minutes of the injection. The fetal heart rate, blood pressure and acid-base status did not change after the injection of nicardipine. These observations of pregnant goats suggest that nicardipine might be a useful agent for the treatment of acutely hypertensive crises in pregnant patients.

Extraneous factors and their influences on fetal acid-base status.

The relevance of extraneous factors on fetal and neonatal respiratory gas exchange and acid-base balance must be considered when interpreting umbilical cord blood values. However, although many of these factors can alter these values to a minor degree, the clinical impact is negligible in the unstressed fetus. The more important clinical aspect of these findings is the reassurance that conditions commonly initiated through appropriate clinical endeavors, such as regional anesthesia or tocolysis, generally have no significant adverse effects on the fetus.

Fetal Surveillance in the Intensive Care Unit: Understanding Electronic Fetal Monitoring

Electronic fetal monitoring has become an integral component of current obstetric nursing care. The goals of surveillance are to establish fetal well-being and identify the fetus at risk for asphyxia and death. Fetal heart rate (FHR) responses provide a cardiovascular indication of fetal acid-base status. To evaluate FHR tracings and plan care accordingly, the nurse must understand the physiologic regularity mechanisms of the fetus, baseline patterns, and periodic changes of the fetal heart rate.

Response of Fetal Heart Rate to Scalp Stimulation Related to Fetal Acid-Base Status

The correlation of the response of the fetal heart rate (FHR) to scalp stimulation and the acid-base status of the fetal scalp blood (FSB pH) was studied in 104 term fetuses during labor. The mean FHR was determined for the 5-minute period before the preparation for fetal scalp blood pH determination and 1 minute following FSB pH. The analysis was performed for three pH groups: (a) Normal (pH more than 7.25, = 73); (2) preacidotic (pH 7.20 to 7.25, = 16); and (3) acidotic (pH less than 7.20, = 15). The pH was confirmed at delivery by determination of umbilical cord blood acid-base status. Regression analysis of the number of fetuses responding by changing their heart rate against time was significant only for the nonacidotic fetuses. There was no significant difference in the number of subjects whose mean FHR increased, decreased, or remained unchanged between the three pH groups. Furthermore, there was no difference between the three pH groups in the number of fetuses who demonstrated significant mean heart rate changes (p less than 0.05) following the stimulation compared to those who did not. Further analysis between fetuses in the three pH groups who increased FHR 15 beats/min or more following stimulation did not discriminate between groups. We conclude that scalp stimulation results in a FHR response in all three pH categories. However, the net change in the mean heart rate following the stimulation may be negative or positive. The magnitude and the direction of this change in FHR is not significantly related to FSB pH.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of fetal sepsis on umbilical cord blood gases

The relationship between fetal sepsis and acid-base status is unknown. We hypothesized that in utero sepsis would result in fetal metabolic acidemia. In a retrospective study during a 38-month period, the acid-base status at birth of neonates with in utero sepsis, documented by positive blood cultures, was reviewed. Compared with term neonates, preterm neonates had a 22-fold increase in the risk of bacteremia at birth. In spite of this increased risk of sepsis, there was no significant alteration in arterial pH in preterm septic neonates when compared with preterm controls. Fetal sepsis at term was accompanied by a statistically significant reduction in arterial pH (7.21 +/- 0.07) compared with controls (7.26 +/- 0.06, p less than 0.05). When controlled for other variables, the decrease in arterial pH at term was correlated with an increased duration of labor (7.3 +/- 0.7 in controls vs 10.8 +/- 0.9 hours in neonates with sepsis, p less than 0.05). The classic predictors of chorioamnionitis were found to be poor prognostic indicators of fetal bacteremia. Fetal sepsis at term is associated with a deterioration in the fetal acid-base status and a prolongation of labor.

Is fetal acidosis in the human fetus maternogenic during labor? A reanalysis

The purpose of this study was to investigate whether maternogenic fetal acidosis can occur at the time of labor and delivery and to evaluate the extent of the possible maternal contribution to fetal acidosis. We have therefore determined fetal and maternal lactate concentrations and acid-base status under various conditions in 589 women at the end of gestation and during labor. The results show that metabolic acidosis develops in all fetuses because of increased production of lactic acidosis is primarily of fetal origin: 1) the umbilical arteriovenous lactate differences were positive and large in steady-state conditions as well as in depressed newborns; 2) the conditions that could produce a net transfer of lactate from the mother to the fetus, namely a positive maternofetal gradient of lactate and proton, were rarely observed; and 3) the correlation between fetal and maternal lactate levels was very weak, with regression coefficients decreasing from near steady-state conditions to acute stress conditions, indicating that the increase in lactate in the fetus and mother occurs independently. This correlation indicates also that increased maternal lactate production under conditions of labor and delivery can make a contribution by affecting the rate of net transfer from fetus to mother. This is possible in approximately 6% of the fetuses.

Amnioinfusion increases amniotic pressure in pregnant sheep but does not alter fetal acid-base status

To investigate the recent suggestion that fetal hypoxemia and acidemia in polyhydramnios are secondary to raised amniotic pressure, 5 to 15 L of normal saline solution was infused intraamniotically at 100 ml/min in seven ewes. Amniotic pressure increased linearly by 1.0 +/- 0.013 (mean +/- SEM) mm Hg per liter infused. Infusion of 15 L produced a mean rise in amniotic pressure of 15.2 +/- 1.2 mm Hg (p less than 0.001) but no significant change in fetal pH, PCO2, PO2, fetal heart rate, or mean arterial pressure. A similar rise in amniotic pressure and lack of change in blood gas values occurred in two control ewes infused intraperitoneally. Rupture of the membranes occurred in two of three amnioinfusions of 15 L. We conclude that acute amnioinfusion raises amniotic pressure in sheep but does not alter fetal blood gas status.

Amnioinfusion increases amniotic pressure in pregnant sheep but does not alter fetal acid-base status

Amnioinfusion increases amniotic pressure in pregnant sheep but does not alter fetal acid-base status

Fetal blood sampling in patients undergoing elective cesarean section: A correlation with cord blood gas values obtained at delivery

The purpose of this study was to compare blood gas parameters obtained after delivery and cord clamping with those obtained in the intact fetal circulation. Eighteen patients undergoing elective cesarean section at term were studied. Before the induction of epidural anesthesia, cordocentesis was performed under ultrasonographic guidance. Subsequently, a second sample was obtained for cord blood gas analysis after delivery. Umbilical venous blood was analyzed for pH, Po2, Pco2, and base excess. When comparing samples obtained from the intact fetal circulation with those obtained after delivery, there was a significant difference in pH (7.36 ± 0.03 vs 7.31 ± 0.04; p \\lt 0.0001 ), Pco2 (41.15 ± 3.66 vs 46.29 ± 5.71; p \\lt 0.018), Po2 (32.92 ± 8.54 vs 26.97 ± 4.43, p \\lt 0.02), and base excess (- 0. 79 ± 1.19 vs -2.36 ± 1.48; p \\lt 0.0003). These results should be considered when cord blood gas values obtained at delivery are correlated with those from the prenatal fetal state. Blood gas values obtained at delivery may not reflect the true prenatal fetal acid-base status.

Cordocentesis in isoimmunization and fetal physiologic measurement, infection, and karyotyping

Diagnostic cordocentesis is indicated in situations that require fetal vascular access. These include detection of intrauterine TORCH infections, estimation of the extent of fetal anemia before initiating therapy for isoimmunization and determination of fetal hematocrit for appropriate timing of subsequent transfusions. It may also be applied to evaluate fetal acid-base status and rapid karyotyping in fetuses with structural anomalies, intrauterine growth retardation, or oligohydramnios. More recently, it has been used to assist in the diagnosis of intrauterine starvation. Therapeutic applications of cordocentesis include intrauterine transfusion and the administration of medications directly to the fetus. Complications inherent to this procedure include cord hematoma and placental abruption.

233 Fetal acid-base status: Does cesarean section without labor have an effect?

233 Fetal acid-base status: Does cesarean section without labor have an effect?

Limited role of fetal blood sampling in prediction of outcome in intrauterine growth retardation

Fetal acid-base status was evaluated on 66 blood samples taken for rapid karyotyping from 58 growth-retarded fetuses. Before blood sampling, doppler blood flow studies of the umbilical artery showed end-diastolic frequencies to be absent in 32 fetuses (group 1) and present in 26 (group 2). Fetuses with chromosomal (n=4) or structural (n=8) abnormalities were excluded from subsequent analysis. Gestational age at blood sampling (27·8 [95% Cl 26·5-29·1] vs 32·2 [30·4-34·1] weeks) and time from sampling to delivery (median 2 (range 0-35] vs 14 [0-77] days) were significantly lower in group 1 than group 2. There were no perinatal deaths in group 2 whereas mortality in group 1 was 65·4%. There were significant differences between the groups at blood sampling in pH, pO2, pCO2, base equivalents, and nucleated-red-cell count, but within group 1 these measurements were similar in surviving fetuses and those who died perinatally. Since acid-base determination does not predict perinatal outcome in growth-retarded fetuses, fetal blood sampling has a limited role in monitoring fetal wellbeing.

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.

Evaluation of Fetal and Neonatal Acid-Base Status

Determination of fetal acid-base status, either at birth, intrapartum, or antepartum, is the gold standard for the diagnosis of fetal asphyxia. Indirect methods such as Apgar scores and fetal heart rate monitoring show at best only minimal correlation. It is evident that intrauterine hypoxia is a rare cause of central nervous system injury, and the finding of a normal acid-base status at birth should lead the clinician to search for other causes of central nervous system injury or birth depression. A combination of techniques including fetal acid-base assessment, electronic fetal heart rate monitoring, and thorough neonatal evaluation probably provides the best predictor of long-term outcome. Newer methods of umbilical cord sampling and acid-base determinations in the intrauterine growth retarded fetus hold some hope for the future.

Noninvasive assessment of fetal aortic blood flow in normal and abnormal pregnancies.

Fetal blood flow measurements have a good capacity to predict unfavorable fetal outcome, especially chronic distress accompanied by IUGR. The descending thoracic aorta is of particular interest in these studies and the results reflect peripheral vascular resistance, both in the fetal placental circulation and in fetal abdominal and peripheral areas. A pathologic finding in blood velocity waveforms, especially an absent end-diastolic velocity, seems to be an early and consistent alteration that precedes the occurrence of a pathologic CTG pattern by at least several days. According to our experience, the main benefit of fetal blood flow studies is in differentiation between IUGR fetuses, in which growth retardation is accompanied by some degree of fetal hypoxia, and those cases in which the small size does not signify an immediate threat to fetal well-being. Nevertheless, there are still a number of diagnostic and practical problems. The individual fetal capability to tolerate impaired fetal placental circulation and hemodynamic redistribution is variable. Hence, it is impossible to make clinical decisions based only on hemodynamic findings; we also need diagnostic support from other methods (evaluation of fetal structures by ultrasound, CTG registration, rapid fetal karyotyping, and fetal acid-base status). In some cases, pathologic blood velocity waveforms develop as soon as at weeks 24-27, and because of the lack of reliable therapeutic methods to improve fetal condition, the selection of an ideal time of delivery is often a compromise between threatened fetal asphyxia and prematurity.(ABSTRACT TRUNCATED AT 250 WORDS)

Meconium in the Amniotic Fluid and Fetal Acid-Base Status

Of 323 pregnancies with meconium-stained amniotic fluid at 36-42 weeks' gestation, 68 (21%) had a pH less than 7.20 in umbilical arterial blood, 21 (7%) had a pH less than 7.15, and only three newborns (0.9%) had true metabolic acidemia. At birth, of the 74 newborns with normal electronic fetal heart rate (FHR) tracings, eight (11%) had an umbilical arterial pH less than 7.20. There was a significantly higher frequency of acidemia (defined as pH less than 7.20) in newborns with both baseline and periodic FHR abnormalities. Although there was a significant difference (P less than .05) in the frequency of meconium found below the cords in these neonates with an umbilical artery pH less than 7.20 compared with those with values exceeding 7.20, there was no significant difference in the frequency of clinical meconium aspiration syndrome. We conclude that meconium-stained amniotic fluid correlates poorly with infant condition at birth as reflected by umbilical cord acid-base measurements.

Assessment of the Fetus: Relevance to Brain Injury

This article reviews recent advances in the antepartum and intrapartum assessment of the fetus and their relationship to brain injury in the newborn. The antepartum assessment involves observation of fetal body and eye movements, the nonstress and contraction stress tests, measurement of amniotic fluid volume, the fetal biophysical score and measurement of fetoplacental blood physiology. There is evidence to suggest that seizures may either be epileptic in origin or initiated and mediated by nonepileptic mechanisms. Therapeutic decisions may be based on bedside assessment of the pathophysiology of observed seizures. Although EEG/video monitoring plays a role in the management of neonatal seizures, clinical evaluation of the seizures may provide initial data critical to decisions concerning immediate management.

Diagnostic cordocentesis: two years of experience

The first diagnostic cordocentesis was performed in our unit in October 1985, our 2-year experience is reported. 144 samplings were performed in 137 patients (139 fetuses — 2 patients had twin pregnancies) during gestational weeks 14 to 42. The first attempt was successful in 80% of the procedures, 4 samplings failed. There were no fetal deaths within 3 days after diagnostic cordocentesis, a transient fetal bradycardia was observed in 12.2% of the cases, bleeding occurred in 13.6% of the cases. The indications for cordocentesis were: risk of fetal infection, karyotyping, hemophilia A, alloimmunisation, search for paternity, assessment of fetal acid-base status. Our data confirm that cordocentesis is a safe and reliable diagnostic procedure providing guidelines for management of the pregnancy.