Labor and fetal heart rate decelerations: relation to fetal metabolic acidosis

Although intrauterine fetal compromise during labor accounts for a small proportion of cerebral palsy cases, fetal hypoxic-ischemic encephalopathy remains an important and sometimes preventable etiology. This paper reviews the mechanisms regulating fetal heart rate responses, pathogenesis of fetal metabolic acidosis, and thresholds for metabolic acidosis associated with hypoxic-ischemic encephalopathy. The knowledge of normal changes in fetal metabolic acidosis during labor together with changes in association with fetal heart rate decelerations, can aid in the interpretation and management of fetal heart rate tracings.     

羊膜腔输注药物治疗羊水过少并发胎儿窘迫的临床效果观察

目的探讨羊膜腔输液、羊水置换及羊膜腔输注碱性药物治疗胎儿窘迫酸中毒的临床效果。方法对40例羊水过少、产程中胎心监护出现胎心律异常波形、Ⅱ度以上羊水胎粪污染产妇,在持续内监护下行羊膜腔输液、羊水置换治疗,其中20例分娩前行羊膜腔输入5%NaHCO3150ml(研究组),20例分娩前行静脉注射5%NaHCO3150ml(对照组),分娩后立即抽取两组新生儿脐动脉血行血气分析,并对两组新生儿行Apgar评分比较。结果(1)羊膜腔输液治疗:两组40例产妇中胎心律异常波形消失27例(27/40,68%),胎心律异常波形明显减少8例(8/40,20%),治疗有效率为88%(35/40);无变化或加重5例(5/40,13%)。(2)羊水置换治疗:两组40例产妇平均每例羊水置换Ⅱ~Ⅲ度胎类污染羊水900ml,最少700ml,最多1200ml。经羊水置换后抽出羊水清亮者21例(21/40,53%),羊水Ⅰ度污染者13例(13/40,33%),有效率为85%(34/40);仍有羊水Ⅱ度污染6例(6/40,15%)。(3)研究组脐动脉血二氧化碳分压(PCO2)、氧分压(PO2)、碳酸氢盐(HCO3-)、剩余碱(ABE)、标准碱(SBE)等指标明显好于对照组,两组比较,差异均有统计学意义(P<0·05,P<0·01)。(4)研究组新生儿出生后1分钟Apgar评分平均为(9·2±1·1)分,对照组平均为(8·7±1·7)分,两组比较,差异有统计学意义(P<0·05)。结论羊膜腔输液及羊水置换是治疗因胎儿窘迫及预防新生儿胎粪吸入综合征的有效方法,羊膜腔输注碱性药物能有效纠正胎儿酸中毒。     

Comparison of intrapartum fetal heart rate tracings in patients with neonatal seizures vs. no seizures: what are the differences?

OBJECTIVE: To determine which intrapartum fetal heart rate parameters in the presence of severe neonatal acidosis (pH < 7.0) appropriately predicts the development of neonatal seizures in the context of hypoxic ischemic encephalopathy (HIE). METHODS: The intrapartum fetal heart rate tracings of 25 neonates who developed neonatal seizures secondary to HIE were compared with 25 matched neonates with similar pH and gestational age who did not develop seizures. All patients had at least 2 hours of intrapartum fetal heart rate patterns available for review. We compared the fetal heart rate parameters of prolonged deceleration, variable and late decelerations, variability, accelerations, fetal heart rate baseline and duration of the fetal heart rate abnormality. Comparison between the groups was done using chi-square for nominal data and student t-tests for continuous data. RESULTS: Neonates with seizures 2 degrees HIE had a significantly longer duration of abnormal fetal heart rate patterns (72 +/- 12 minutes vs 48 +/- 12 minutes, p < 0.001). DISCUSSION: This study demonstrated that in the setting of neonatal acidosis the development of seizures is related to the period of stress (duration of the abnormal fetal heart rate pattern).     

The slope of fetal heart rate deceleration is predictive of fetal condition during repeated umbilical cord compression in sheep

The relationship between components of fetal heart rate deceleration and fetal arterial blood gas values or plasma catecholamine concentrations was investigated by repeated complete umbilical cord compression in chronically instrumented fetal lamb. Fetal arterial pH and bicarbonate levels decreased, while plasma norepinephrine and epinephrine concentrations increased more than tenfold. The slope of the descending limb of the fetal heart rate deceleration curve decreased and correlated strongly with fetal arterial pH, bicarbonate, and logarithmic plasma norepinephrine and epinephrine concentrations. Fetal arterial pH and bicarbonate levels were significantly lower in the group with lower fetal heart rate deceleration slope, and a greater plasma catecholamine concentration in this group suggested a redistribution of blood flow to vital organs. Therefore, during repeated umbilical cord compression, the fetal acid-base and hormonal state was predicted by the fetal heart rate deceleration slope. This relationship may be applicable to human fetuses in the diagnosis of fetal distress caused by umbilical cord compression during labor.     

The Influence of Maternal Bearing-down Efforts during Second Stage on Fetal Well-being

ABSTRACT: Fetal heart rate patterns, and intrauterine and maternal blood pressures were recorded during various types of maternal bearing-down efforts. Bearing-down efforts which lasted more than 5 seconds resulted in late decelerations of the fetal heart rate, marked falls in the maternal systolic and diastolic blood pressures and resultant delayed recovery of the fetal heart rate, with fetal hypoxia and acidosis in some cases. When women are not urged to bear down long and hard, their spontaneous efforts are usually within physiologic limits-5–6 seconds long-and fetal acidosis is thereby avoided.     

Metformin-associated lactic acidosis in a pregnant patient

Metformin-associated lactic acidosis is a rare but serious condition and potentially even more hazardous during pregnancy. We reported a case of lactic acidosis in a 28-year-old pregnant woman (gravida 3, para 0, abortion 2, ante-partum 22 weeks) after ingestion of 39.50 g (approximately 80 tablets) metformin in a suicide attempt. She had no pre-existing systemic illness. Analysis of arterial blood gases revealed a high anion gap (28.1 mEq/l) and a normal osmol gap (8 mEq/l) metabolic acidosis. Other etiologies of high anion gap and normal osmol gap metabolic acidosis were excluded by laboratory investigation. The patient was treated on an emergency basis and received aggressive fluid management, intravenous sodium bicarbonate (1 mEq/kg) and activated charcoal, orally. The fetal condition was monitored intensively. The fetus was delivered smoothly via vaginal delivery in a healthy state at the 38th gestational week. Clinical follow-up over the next 2 years confirmed no congenital abnormality. We present a case of successful management of metformin-associated lactic acidosis during pregnancy, treated simply, with intravenous sodium bicarbonate and intensive fetal monitoring. This relatively noninvasive method is an effective treatment option. However, hemodialysis still has a valuable role in the management of acidosis which proves refractory to conservative treatment, such as that described.     

产程中的胎儿监护

胎心率受到自主神经系统、化学感受器等多因素影响,是胎儿心脏和延髓对母胎血供、酸中毒和缺氧情况的反映。产时胎心监护用于评估胎儿宫内情况,可分为三级胎心率。根据产时胎心监护对患者进行科学分级管理,将有利于及时识别和处理胎儿宫内缺氧和酸中毒,预防胎儿死亡。     

Permeability of the human placenta to bicarbonate: in-vitro perfusion studies

Summary. The effect of maternal acidosis on fetal acid-base balance was studied in a dual circuit perfusion of a single cotyledon in normal, term, human placentas. Both the fetal and maternal (intervillous) circulations were perfused with a Krebs-Ringer solution adjusted to pH values between 7.35 and 7.45. After a control period, the perfusate in the maternal circulation was replaced by an acidified medium (mean pH 7.06) for 30 min. This was followed by a second control period of 30 min during which the acidified maternal perfusate was replaced with the original medium. During the 30 min of maternal acidosis, fetal vein pH was not significantly altered despite the large decrease in maternal artery pH, but there was an efflux of total CO₂ (tCO₂) from the placenta into the maternal circulation which was not matched by an influx of tCO₂ from the fetal circulation. The tCO₂ transferred was in the form of bicarbonate rather than dissolved CO₂, but the maximal rate of tCO₂ transfer of in the form of bicarbonate was lower than the rate of placental transfer of tCO₂ necessary in vivo . It is probable therefore that bicarbonate does not play a major role in placental CO₂ transfer but the placental tissue bicarbonate pool may play an important part in buffering the fetus against changes in maternal pH or blood gas status.     

Relationship between cyclic variation of fetal heart rate patterns and cord pH in preterm gestations

The presence or absence of cyclic variation (cyclicity) of fetal heart rate patterns was prospectively investigated in fetuses between 25 and 32 weeks' gestation. All fetuses were delivered by cesarean section before the onset of labor. The relationship between the presence or absence of fetal heart rate cyclicity and fetal acidosis, as determined by cord pH measurements, was investigated. The sensitivity, specificity, positive predictive value, and negative predictive value of this method in predicting fetal acidosis were: 100, 90, 50, and 100%, respectively. All fetuses with reactive nonstress tests also had fetal heart rate cyclicity present and none were acidotic at birth. The majority of fetuses (68.8%) with nonreactive nonstress tests had fetal heart rate cyclicity present and none were acidotic; fetuses with nonreactive nonstress tests and absence of fetal heart rate cyclicity were acidotic in 50% of the cases. These preliminary data suggest that the presence or absence of fetal heart rate cyclicity may help to select the healthy preterm fetuses with nonreactive nonstress testing who are in good condition and therefore in no need for further testing.     

Changes in fetal acid-base chemistries following tromethamine (THAM) or bicarbonate infusions into fetal circulation of amniotic fluid

Direct infusions of equimolar quantities of bicarbonate and tromethamine into rhesus monkey fetal circulation near term resulted in roughly equivalent increases in fetal pH. However, intra-amniotic infusion of tromethamine was not followed by alkaline changes in the fetus and in most instances was followed by a progressive fetal acidosis. This sharply contrasts with previous experimental success in elevating fetal pH via amniotic fluid bicarbonate infusions.     

ST segment analysis as an adjunct to electronic fetal monitoring, Part I: background, physiology, and interpretation

Fetal electrocardiogram (ECG) ST segment analysis (STAN) was approved in 2005 in the United States as an adjunct to electronic fetal heart rate monitoring to determine whether obstetrical intervention is warranted when there is an increased risk for developing metabolic acidosis. STAN has utility in the reduction of fetal acidosis at birth, decreased need for fetal scalp blood sampling during labor, and decreased need for operative vaginal delivery and emergency cesarean delivery for fetal indications. This article discusses specific fetal ECG changes and their significance and the use of the STAN system.     

Treatment of acute intrapartum fetal distress by beta 2-sympathomimetics

Patients with a diagnosis of severe intrapartum fetal distress by fetal heart rate and capillary blood pH monitoring received beta 2-sympathomimetics to inhibit uterine contractions (tocolysis) while the obstetric team was preparing to deliver the fetus. Fetal heart rate and acidosis significantly improved after tocolysis; these fetuses were subsequently delivered in very good metabolic and clinical condition. The favorable effect of tocolysis on fetal homeostasis is attributed to the suppression of the ischemic effect of contractions on the placental circulation. The few fetuses having an extremely compromised placental function showed no improvement in heart rate or acidosis with tocolysis and were immediately delivered. Considering the mild side effects observed, the lack of maternal complications, and the remarkable perinatal outcome obtained, we recommend using tocolysis before delivering distressed fetuses.     

The scalp stimulation test: a clinical alternative to fetal scalp blood sampling

Intrapartum fetal heart rate response to various scalp stimuli and its correlation with scalp pH was studied in a prospective manner. One hundred fetuses with heart rate tracings judged by the resident responsible for the patient to be suggestive of fetal asphyxia were entered into the study. Each fetus was subjected to firm digital pressure on the head followed by a gentle pinch of the scalp with an atraumatic clamp. Scalp blood sampling was then performed in the usual manner. Response to either of these stimuli by an acceleration of the fetal heart rate of 15 bpm lasting at least 15 seconds was uniformly associated with a scalp blood pH of greater than or equal to 7.19. Fifty-one fetuses so stimulated responded with an acceleration. Of the remaining fetuses, 19 had a scalp pH less than 7.19 and 30 were associated with a pH greater than 7.19. Clinical application of such a scalp stimulation test could, therefore, reduce the necessity for scalp blood sampling by approximately 50% in the presence of a fetal heart rate pattern suggesting acidosis. Such a provocative test may also be very useful with an abnormal fetal heart rate pattern suggestive of acidosis when the cervix is sufficiently dilated to permit scalp blood sampling.     

Marked fetal acidosis and specific changes in power spectrum analysis of fetal heart rate variability recorded during the last hour of labour

OBJECTIVE: To assess whether intrapartum acidosis affects specific components of fetal heart rate variability. DESIGN: Prospective clinical study. SETTING: Twelve Nordic delivery units. SUBJECTS: Fetal heart rate variability was studied in 334 fetuses divided into two groups according to cord pH value: the acidotic group (cord arterial pH < 7.05 at birth, n= 15) and the control group (cord arterial pH > or =7.05 at birth, n= 319). METHODS: In spectral analysis of fetal heart rate variability, frequencies were integrated over the total frequency band (0.04-1.0 Hz), low-frequency band (0.04-0.15 Hz) and high-frequency band (0.15-1.0 Hz). We also calculated the low-to-high frequency ratio. MAIN OUTCOME MEASURES: The spectral bands of fetal heart rate variability were compared between the acidotic and control fetuses. RESULTS: We found that during the last hour of monitoring, baseline fetal heart rate gradually decreased, whereas total, low-frequency and high-frequency fetal heart rate variability initially increased but then, near the delivery, decreased in the acidotic fetuses when compared with the controls. Low-to-high frequency ratio was greater in the acidotic group during the whole study period (P= 0.002). Cord artery pH was inversely associated with total fetal heart rate variability (P < 0.001), low-frequency fetal heart rate variability (P < 0.001) and low-to-high frequency ratio (P= 0.004). CONCLUSIONS: Marked fetal acidosis was associated with frequency-specific changes in fetal heart rate variability as reflecting the compensation ability of autonomic nervous activation during the last hour of labour.     

Intramuscular pethidine (meperidine) during labor associated with metabolic acidosis in the newborn

Analyses of fetal heart rate (FHR) variability, visual evaluation of FHR decelerations, and respiratory gas analyses of the umbilical vein were performed in 27 labors, where one dose (50 or 75 mg) of intramuscular pethidine was used for pain relief, in 47 labors with one paracervical blockade (6 ml 0.5% marcaine) and in a control group of 135 labors without any pain relief. Umbilical vein pH, standard bicarbonate and base excess were lowest in the pethidine group and highest in the PCB group. The duration of labor was shortest in the control group, but there was no difference in the duration of labor of the two anesthesized groups. Intramuscular pethidine seems to associate with umbilical metabolic acidosis and PCB should be preferred to it, when an obstetrician is available.     

Effect of acetaminophen on fetal acid-base balance in chorioamnionitis

The effect of antipyretic treatment with acetaminophen on fetal status was examined in eight laboring women febrile with chorioamnionitis. After a fetal heart rate tracing and scalp blood gas level were obtained near maximum maternal fever, a 650-mg acetaminophen suppository was administered. If the temperature remained greater than 101 degrees F, the dose was repeated in one to two hours. The fetal heart rate tracing was analyzed again after the mother's fever was reduced by acetaminophen. All patients delivered within four hours of the first dose. Umbilical artery blood gases were obtained at delivery. Significant improvements in the bicarbonate concentration and base deficit were noted at the time of delivery as compared to the scalp gas at the height of the maternal fever. The fetal heart rate tracings at the height of the maternal fever, characterized by tachycardia, poor variability and late decelerations, changed to a normal heart rate pattern without decelerations when the mother's fever was reduced. Hence, in the laboring gravida with chorioamnionitis, reducing maternal fever with acetaminophen improves fetal status and thereby may reduce the probability of cesarean section for fetal distress.     

Usefulness of the examination of fetal blood oxygen saturation (FSpO2) and fetal heart rate (FHR) as a prognostic factor of the newborn outcome

OBJECTIVES: Cardiotocography has become the standard for fetal monitoring in labor. False-positive findings during electronic fetal heart rate monitoring may were not associated with neonatal acidemia. Because of the poor specificity of fetal heart rate monitoring in predicting fetal distress, new methods are being investigated as a way to improve the accuracy of assessing the infant's condition during labor. DESIGN: The aim of this study was to determinate the efficiency of fetal blood oxygen saturation (FSpO2) and computer analysis of the fetal heart rate (Co-CTG) in the late 1-st stage of labor as a prognostic factor of newborn acidemia. MATERIALS AND METHODS: Total 62 subjects were studied. During labors and deliveries fetal oxygen saturation was continuously recorded, with use of Nellecor N-400 fetal pulse oximeter and continous CTG were performed by Hewlett Packard 50A. Transdermal fetal oxygen saturation measurements and CTG results obtained during the labors was analyzed using MONAKO system (ITAM Zabrze). The results were compared with the values of pH and base deficit in the umbilical artery measured just after delivery. RESULTS: The sensitivity, specificity, negative, positive predictive values and Youden factor based on FHR and FSpO2, for prognosis of neonatal acidosis were: 65%, 80%, 16%, 97.5% 60% and 0.135 respectively FHR; and 100%, 60%, 100%, 96.8% and 0.968 respectively FSpO2. CONCLUSIONS: 1. The examination of fetal blood oxygen saturation in the labor is a useful prognostic factor of the newborn outcome. 2. The best predictive value for intrapartum fetal asphyxia with metabolic acidosis was found when fetal pulse oximetry is added to cardiotocography.     

Single injection of terbutaline in term labor. I. Effect on fetal pH in cases with prolonged bradycardia

Thirty-three patients with prolonged fetal bradycardia (fetal heart rate baseline less than 100 bpm for a minimum of 3 minutes or less than 80 bpm for at least 2 minutes) in labor were studied. They were treated with a bolus injection of terbutaline if the bradycardia persisted at less than 80 bpm for 2 minutes and other efforts to improve the fetal heart rate (oxygen, positional changes) had failed. After the bolus injection a scalp blood pH (or a cord arterial pH in abdominal deliveries) was obtained within 30 minutes. Fetal acidosis was common if the bradycardia lasted 10 minutes or more, particularly if the rate was less than 80 bpm with a flat baseline for 4 minutes or more. The fetal heart rate improved after injection in 30 cases; 23 patients had vaginal delivery of infants in good condition. Ten underwent cesarean section: three for no improvement in fetal heart rate, two for cord prolapse, four for later ominous fetal heart rate, and one for failure to progress. These results suggest that tocolysis in selected cases can be of benefit for the fetus with prolonged bradycardia. In cases with an ominous fetal heart rate pattern preceding the bradycardia and in abruptio placentae immediate operative intervention without delay is probably better. Administration of terbutaline should be regarded as a temporary measure until it is apparent that the fetal heart rate has recovered. Preparation for emergency delivery should be made while a recovery is awaited.     

Fetal acidosis in prolonged pregnancy cannot be attributed to cord compression alone

Fetal heart rate abnormalities associated with prolonged pregnancy have been attributed to umbilical cord vulnerability rather than placental insufficiency. Although intrapartum fetal heart rate patterns indicative of umbilical cord compression are common beyond 41 weeks' gestation, fetal intolerance to labor develops only in a subset of such patients. To test the hypothesis that suboptimal placental function contributes to reduced amniotic fluid volume and, ultimately, to fetal intolerance to labor, we prospectively collected biochemical and clinical data on 112 prolonged pregnancies. Data analysis was blinded to outcome and included cord blood acid-base measurements and intrapartum fetal heart rate interpretation. We observed a high incidence of umbilical cord compression (46.4%), but this finding was not predictive of emergent delivery in 32 of 52 cases (61.5%). Fetal acidosis (arterial pH less than 7.20) occurred more often in patients with cord compression, but the anticipated increase in carbon dioxide tension was not observed. Instead, a primary metabolic or combined acidosis was encountered in those fetuses delivered emergently. The additional findings of lower amniotic fluid volume and diminished birth weight in those patients delivered for fetal intolerance to labor suggest a direct role for suboptimal placental function in selected patients with prolonged pregnancy.     

Fetal heart rate patterns in the small-for-gestational-age human fetus

A total of 24 pregnant women with growth-retarded fetuses were studied to examine the distribution of fetal heart rate accelerations between 30 and 40 weeks' gestation, as compared with those of fetuses of normal growth that were matched for gestational age and length of fetal heart rate tracings. Growth-retarded fetuses had significantly lower PO2 levels in the umbilical artery at birth (3 mm Hg less) than did healthy fetuses (p less than 0.05), but without metabolic acidosis. There was a larger proportion of small amplitude (less than 10 beats/min) and a smaller proportion of large amplitude (greater than 20 beats/min) fetal heart rate accelerations in the small-for-gestational-age fetuses than in the fetuses of normal growth. Although the number of accelerations was significantly reduced (50% less) in growth-retarded fetuses compared with healthy fetuses, there was no significant difference in the mean basal fetal heart rate and the mean number of decelerations between the two groups. Currently used definition of an acceleration as greater than or equal to 15 beats/min for greater than or equal to 15 seconds was applicable only in fetuses of normal growth. We hypothesized that a decrease in absolute acceleration frequency might be a useful index to detect the chronically hypoxemic fetus before severe metabolic acidosis and irreversible damage occurred.