Relationship of fetal bradycardia to maternal administration of lidocaine in sheep.

The casual relationship between the use of lidocaine and fetal bradycardia and the effect of the drug on maternal and fetal hemodynamics were studied on 13 chronically instrumented pregnant sheep. Lidocaine was infused intravenously to the mother for 60 minutes during arterial lidocaine concentrations were maintained at 2 to 5 microgram per milliliter in the mother and at less than 2 microgram per milliliter in the fetus. A decrease in uterine blood flow and an increase in uterine vascular resistance and uterine activity occurred immediately following the administration of lidocaine to the ewe. These changes were followed by a transient fetal bradycardia in 12 out of 17 experiments, accompanied by a decrease in fetal PaO2 values. These phenomena were seen in the absence of such predisposing conditions as maternal hypotension and fetal acidosis. It would appear that the mechanism responsible for a transient fetal bradycardia following regional obstetric anesthesia, particularly paracervical block anesthesia, in the initially nonasphyxiated fetus may in part be related to a brief decrease in perfusion of intervillous spaces. The bradycardia can occur at low lidocaine concentrations in both the maternal and fetal blood in a range similar to that observed in clinical practice.     

Thrombosis of the right umbilical artery, presumably related to the shortness of the umbilical cord: an unusual cause of fetal distress

This case report concerns a late pregnancy complication, clinically apparent as severe variable decelerations in the first stage of labor. Emergency cesarean section delivered a mildly asphyxiated full-term newborn infant. Examination of the umbilical cord revealed a thrombus of the right umbilical artery, near the fetal side, confirmed by histological examination. The total length of the umbilical cord, only 30 cm, was below the limit necessary for uncomplicated delivery of the fetus near term. Transient stretching during fetal descent is thought to be responsible for constriction of the umbilical arteries, blood flow sludging and thrombosis. Although only a few cases have been reported, thrombosis of the umbilical vessels has to be considered whenever the fetal heart rate pattern shows unexplained variable decelerations.     

Acute effects of maternal smoking on fetal blood flow

Thirty healthy pregnant women were studied to assess the immediate cardiovascular responses of the fetus to the smoking of one cigarette. The fetal blood flow was measured in the aorta and in the umbilical vein by combining real-time ultrasonography and the pulsed Doppler technique. Following maternal smoking, a significant increase was found in the maternal heart rate and also in the blood pressure. In the fetus, a significant transient increase in the aortic and the umbilical blood flow was measured, as characterized by the increase in the fetal heart rate, the mean and maximum blood velocity, and the vessel diameter. Thus, maternal smoking induced acute circulatory changes in the fetus similar to those found in adults. Furthermore, the study demonstrated the feasibility of the method to evaluate non-invasively the immediate effect of a given stress stimulus on the cardiovascular system of the human fetus.     

Fetal volume blood flow and umbilical artery flow velocity waveform analysis: a comparison

Summary. The estimation of fetal umbilical vein and aortic volume blood flow was compared with umbilical artery flow velocity-time waveform analysis in 42 pregnancies. The volume blood flow measurements were made with a combined linear array B-mode and pulsed Doppler ultrasound system. The umbilical artery flow velocity-time waveform analysis was made with either pulsed or continuous wave 2 MH_zDoppler ultrasound and the systolic/diastolic (A/B) ratio was used as an index of flow resistance. There was no difference when continuous wave was compared to pulsed Doppler ultrasound as a method of recording flow velocity waveforms. Analysis of the umbilical artery flow velocity-time waveform was more sensitive (100%-50%) than the measurement of umbilical vein volume blood flow (ml/kg/min) in the detection of the small-for-gestational age (SGA) fetus. The predictive value of a positive test was higher (71%-45%) while specificity was similar (88%-81%). Descending aortic volume flow was reduced in only one SGA fetus. The increase in umbilical placental downstream resistance (high systolic/ diastolic ratio) was associated with a reduction in the percentage of fetal aortic blood flow directed to the umbilical placental circulation.     

The effect of insulin on ovine fetal oxygen extraction

Infusion of exogenous insulin (54 +/- 19 mU/kg/hr) to seven fetal lambs caused hyperinsulinism and arterial hypoxemia but not hypoglycemia. We measured the relationship between fetal oxygen delivery and oxygen use for a better understanding of the cause of the observed hypoxemia. Oxygen delivered to the fetus is the product of fetal umbilical venous oxygen content and umbilical blood flow. Both of these quantities decreased as fetal insulin concentration rose. The fall in umbilical blood flow was due to a change in the distribution of cardiac output. Cardiac output rose, but placental perfusion decreased while blood flow to the fetal carcass increased. Oxygen consumption by the ovine fetus increased as insulin concentration rose. Since the delivery of oxygen to the fetus did not increase when its use was rising, fetal extraction of available oxygen increased. Fetal arterial hypoxemia is the result of this increased extraction of available oxygen.     

Fetal volume blood flow and umbilical artery flow velocity waveform analysis: a comparison

Summary. The estimation of fetal umbilical vein and aortic volume blood flow was compared with umbilical artery flow velocity-time waveform analysis in 42 pregnancies. The volume blood flow measurements were made with a combined linear array B-mode and pulsed Doppler ultrasound system. The umbilical artery flow velocity-time waveform analysis was made with either pulsed or continuous wave 2 MH_zDoppler ultrasound and the systolic/diastolic (A/B) ratio was used as an index of flow resistance. There was no difference when continuous wave was compared to pulsed Doppler ultrasound as a method of recording flow velocity waveforms. Analysis of the umbilical artery flow velocity-time waveform was more sensitive (100%-50%) than the measurement of umbilical vein volume blood flow (ml/kg/min) in the detection of the small-for-gestational age (SGA) fetus. The predictive value of a positive test was higher (71%-45%) while specificity was similar (88%-81%). Descending aortic volume flow was reduced in only one SGA fetus. The increase in umbilical placental downstream resistance (high systolic/ diastolic ratio) was associated with a reduction in the percentage of fetal aortic blood flow directed to the umbilical placental circulation.     

Fetal volume blood flow and umbilical artery flow velocity waveform analysis: a comparison

The estimation of fetal umbilical vein and aortic volume blood flow was compared with umbilical artery flow velocity-time waveform analysis in 42 pregnancies. The volume blood flow measurements were made with a combined linear array B-mode and pulsed Doppler ultrasound system. The umbilical artery flow velocity-time waveform analysis was made with either pulsed or continuous wave 2 MHz Doppler ultrasound and the systolic/diastolic (A/B) ratio was used as an index of flow resistance. There was no difference when continuous wave was compared to pulsed Doppler ultrasound as a method of recording flow velocity waveforms. Analysis of the umbilical artery flow velocity-time waveform was more sensitive (100%-50%) than the measurement of umbilical vein volume blood flow (ml/kg/min) in the detection of the small-for-gestational age (SGA) fetus. The predictive value of a positive test was higher (71%-45%) while specificity was similar (88%-81%). Descending aortic volume flow was reduced in only one SGA fetus. The increase in umbilical placental downstream resistance (high systolic/diastolic ratio) was associated with a reduction in the percentage of fetal aortic blood flow directed to the umbilical placental circulation.     

Response of the primate fetus to intra-amniotic saline injection.

The amniotic fluid was replaced with 20 per cent sodium chloride solution during the second half of gestation in 12 pregnant rhesus monkeys. This produced a congealing of the fetal blood in the small umbilical vessels which overlie in the placental chorionic plate. Death of severe asphyxia followed within 20 to 50 minutes in the younger fetuses due to a prompt cessation of umbilical blood flow. During this time, the rise in serum sodium of the fetus was moderate and could not be implicated as the cause of fetal death. In older fetuses, the asphyxia produced by the saline injection was transient and less severe, occasionally permitting survival. The caliber of the affected fetal umbilical blood vessels and their blood flow rates are presented as the principal determinants of the rapidity of development and the severity of the asphyxia produced by saline instillation.     

Early-diastolic blood flow velocity block in the umbilical artery and fetal cardiac valvular insufficiency. Case report.

Absence of early-diastolic blood flow velocity was recorded from the umbilical artery of a fetus with severe myocardial and valvular insufficiency. The blood flow at late diastole was normal. This flow pattern may indicate the need for a detailed ultrasonic examination of the fetal heart.     

Effect of endothelium-derived relaxing factor inhibition on the umbilical-placental circulation in fetal lambs in utero.

OBJECTIVE: The purpose of this study was to examine whether basal endothelium-derived relaxing factor release contributes to regulation of resting umbilical-placental vascular resistance. STUDY DESIGN: Because N omega-nitro-L-arginine selectively inhibits the synthesis of nitric oxide, a major endothelium-derived relaxing factor, we investigated the effects of N omega-nitro-L-arginine on umbilical-placental vascular resistance in 10 fetal lambs in utero. We inserted catheters and fitted an umbilical artery electromagnetic flow transducer around the common umbilical artery to measure umbilical blood flow and catheterized the left umbilical arterial hypogastric branch to allow selective umbilical-placental infusion (60 minutes) of pH-matched saline solution (control) or N omega-nitro-L-arginine. RESULTS: In seven normal fetal lambs, N omega-nitro-L-arginine increased umbilical-placental vascular resistance and arterial pressures and decreased umbilical blood flow (p less than 0.05); percentage changes from baseline were 50.8% +/- 18.3%, 40.3% +/- 8.1%, and -9.9% +/- 6.4%, respectively. In three mildly asphyxiated (compromised) fetuses, these changes were 101.4% +/- 28.7%, 31.2% +/- 4.8%, and -37.9% +/- 12.0%. CONCLUSION: These data support the hypothesis that the basal endothelium-derived relaxing factor release plays a role in regulating resting umbilical-placental vascular resistance.     

脐动脉血流监测在产科的应用

脐动脉血流监测做为非侵入性的胎儿胎盘血流动力学评估方法,广泛应用于产科临床。脐动脉多普勒血流波形主要反映胎盘的血管阻力,受绒毛血管发育状况的影响。同时,胎龄、胎儿心率、胎儿呼吸和呃逆、胎动、脐带的采样位置、胎儿性别、胎盘重量及胎儿体重等也对其有一定的影响。循证医学证据推荐将脐动脉超声多普勒检测作为胎儿生长受限及双胎选择性生长受限的胎儿监测。在低危人群中,脐动脉血流监测的意义还存在很多争议。舒张末期血流缺失或反向与围产期结局显著不良相关,需注意排除胎儿先天性异常及非整倍体异常。脐动脉血流异常的产科处理取决于脐动脉多普勒检查结果异常的严重程度、基础产科并发症的严重程度以及孕周,应个体化处理。     

Maternal and fetal cardiovascular indices during fetal hypoxia due to cord compression in chronically cannulated sheep. I. Responses to timolol

Timolol, one of the newer beta-adrenergic antagonists, has less depressive effects on the heart than propranolol, so that it has the potential for use by pregnant women. In chronically cannulated ewes, timolol at 0.01 and 0.1 mg/kg of body weight induced maternal and fetal bradycardia; the higher dose also depressed uterine blood flow and fetal PaO2. When this higher dose preceded brief compression of the umbilical cord, uterine flow was further depressed and the usual posthypoxia rebound tachycardia did not develop. Both the blocking of fetal responses to hypoxia (precluding detection of fetal distress) and the reduction in uterine flow led us to conclude that timolol taken by a mother could pose particular hazards for her fetus in hypoxic conditions, such as during cord compression at parturition.     

Uterine activity: implications for the condition of the fetus

AIM: The aim of this review is to provide more insight in the fetal mechanisms as a response to uterine contractions and to emphasize the importance of correct assessment of uterine activity (UA) patterns during labor. STUDY RESULTS: UA causes a decreased flow through the uterine artery. In the healthy uncompromised fetus, this will not cause fetal acidemia. The fetus has developed certain protection mechanisms to survive labor; (1) During a contraction, fetal preload increases and enables the fetus to maintain a constant blood flow through the umbilical artery and (2) UA increases the blood flow in the fetal middle cerebral artery, i.e., a brain sparing effect. The shortcoming of those protection mechanisms in the compromised fetus and in case of excessive UA increases the risk of adverse fetal outcome. The brain sparing effect will become more pronounced to compensate for the decreased umbilical artery blood flow and fetal oxygen saturation. Maintenance of normal UA, especially a sufficiently long relaxation time, is essential so that the supply of well oxygenated maternal blood to the intervillous space will be restored and the fetal cerebral oxygen saturation can remain stable. CONCLUSION: Adequate UA monitoring is a prerequisite for proper reading and interpretation of cardiotocograms. It alarms in cases of excessive UA and can help to prevent fetal acidemia. Uterine contraction monitoring deserves full attention in daily obstetric practice.     

Influence of nicotine chewing gum on fetal blood flow

Several studies have shown that smoking is not beneficial to the fetus. Among the acute effects, influence on fetal circulation has been reported. Nicotine is considered to be one of the active agents in cigarette smoke. To test the nicotine effects on the human fetus, maternal and fetal cardiovascular dynamics were studied in 20 pregnant women when chewing a chewing gum containing 4 mg of nicotine and a chewing gum without nicotine given in a randomized double blind order. The fetal blood flow was measured with a method combining real-time ultrasonography and pulsed Doppler technique. Registrations were made in ten fetuses from the thoracic part of the descending aorta and in ten fetuses from the intra-abdominal part of the umbilical vein. In 15 of the fetuses registrations were also made from the umbilical artery. Concentrations of nicotine in plasma were analyzed in six women. The maternal plasma nicotine concentrations increased after the nicotine gum to a maximum value of 12.4 ng X ml-1 (median) at 25 min (figure 1). The 4 mg nicotine gum increased significantly maternal heart rate, systolic and diastolic blood pressure (figure 2). There was no influence on fetal heart rate or fetal blood flow, neither in the thoracic part of the descending aorta, nor in the intra-abdominal part of the umbilical vein (figure 3). There were no changes in the waveforms of the maximum blood velocity curves, neither of the aorta nor the umbilical artery. This indicates that there was no increased resistance in the placenta, neither after the nicotine gum nor the placebo gum.(ABSTRACT TRUNCATED AT 250 WORDS)     

静脉导管、脐静脉和脐动脉及大脑中动脉血流检测对子痫前期胎儿预后分析

目的:探讨子痫前期(PE)胎儿静脉导管(DV)、脐静脉(UV)和脐动脉(UA)及大脑中动脉(MCA)血流检测对围生儿预后分析。方法:应用彩色多普勒超声检测PE胎儿的DV、UV和UA及MCA血流参数,并与相应孕周正常妊娠胎儿的血流测值进行对照分析,研究分析其与胎儿不良结局的关系。结果:28~31+6周及36周~分娩前,重度PE胎儿的DV、UV血流测值较正常、轻度PE胎儿升高(P0.05),轻度PE与正常胎儿比较差异无统计学意义(P0.05)。32周~35+6周,PE胎儿的DV血流参数测值PLI、PVIV、PIV及Qdv/Quv随着PE严重程度呈上升趋势(P0.05)。28周~分娩前,重度PE胎儿UA血流测值较正常、轻度PE胎儿升高(P0.05),轻度PE胎儿UA血流测值RI、PI、S/D与正常胎儿比较差异无统计学意义(P0.05),28~36周PE胎儿的MCA血流测值RI、PI、S/D与正常胎儿比较差异有统计学意义(P0.05)。PE胎儿DV、UV、UA血流测值与新生儿的出生体重、Apgar评分、脐动脉血氧饱和度、脐静脉p H值呈负相关。PE胎儿DV的PVIV、PIV,UV的Qdv/Quv,UA的PI、S/D和MCA的RI值与新生儿出生结局相关(P0.05)。结论:DV、UV血流频谱变化可反映PE胎儿宫内状况及预测出生不良结局,若结合UA、MCA血流频谱进行联合分析,将能更准确地评估胎儿的宫内状况。     

The effect of increased maternal PaO2 upon the fetus during labor.

The effect of increased maternal PaO2 upon the fetus during labor was studied in 36 subhuman primates. The animals were divided into two groups, one in which the fetus was not asphyxiated and showed no evidence of fetal distress (Group I) and another in which the fetus was acidotic, hypoxic, and exhibited the pattern of late deceleration of the heart rate (Group II). One hundred per cent oxygen was administered to the mothers for a period of 30 minutes. Elevation of maternal PaO2 to 430 mm. Hg increased fetal oxygen levels in Group I. and in most instances in Group II, without significant changes in the acid-base state. In Group II, maternal hyperoxemia also abolished or reduced the frequency of late deceleration of the fetal heart in most animals but had little or no effect on fetal blood pressure. Termination of high-concentration oxygen to the mother resulted in a fall in maternal and fetal oxygen levels to their original values and the reappearance of late fetal heart decelerations. Thus, administration of high-concentration oxygen to the mother for the treatment of fetal distress may be of some benefit. The problems of fetal acidosis and hypotension are not cured, however, and may still progress if there is placental insufficiency or cord compression. Therefore, this treatment should be regarded as a temporary supportive measure only.     

The acute response of the umbilical artery pulsatility index to changes in blood volume in fetal sheep.

This experimental study was designed to test the effects of acute changes in fetal circulating blood volume on the umbilical artery pulsatility index (PI). Six fetal sheep were provided with an electromagnetic flow meter for measurement of umbilical venous blood flow, with catheters for determination of arterial blood pressure and umbilical venous pressure, and with a 5 MHz Doppler transducer around one umbilical artery for flow velocity waveform analysis. A catheter in the inferior vena cava was used to infuse 50 ml of maternal blood (hypervolemia) into the fetal circulation or to withdraw 50 ml of fetal blood (hypovolemia) after volume correction. Hypervolemia resulted in a rise in arterial pressure and umbilical venous pressure, without an effect on PI, umbilical blood flow or placental vascular resistance. Hypovolemia resulted in a decrease in fetal heart rate, arterial pressure, umbilical venous pressure and umbilical blood flow. Calculated placental vascular resistance was not changed, whereas the PI increased by 42%. We conclude that volume loading with 10-15% of fetal circulating volume does not affect the umbilical artery PI, whereas acute reduction of fetal blood volume with the same amount is associated with an increase in the umbilical artery PI, without changes in calculated placental vascular resistance.     

Fetal umbilical artery flow velocity waveforms and placental resistance: clinical significance

Summary. Since the umbilical arteries carry fetal blood to the placenta we studied flow velocity waveforms in these vessels with a simple continuous wave Doppler system to assess placental blood flow. The ratio of peak systolic to least diastolic (A/B) flow velocity was measured as an index of placental flow resistance. In 15 normal pregnancies there was a small but significant decrease in this ratio through the last trimester. The A/B ratio was measured on 436 occasions in 168 high-risk pregnancies. In 32 of 43 fetuses subsequently shown to be small for gestational age there was an increase in placental flow resistance with reduced, absent or even reversed flow in diastole. This finding was also present in the one fetus which died in utero . Serial studies in patients with fetal compromise indicated increasing flow resistance, a reverse of the normal trend. These results were not available to the clinician yet of 24 fetuses born before 32 weeks 13 had a high A/B ratio, and all of them were born electively. Maternal hypertension was associated with an increase in fetal placental flow resistance. The umbilical artery A/B ratio provides a new and non-invasive measure of fetoplacental blood flow resistance.     

Fetal umbilical artery flow velocity waveforms and placental resistance: clinical significance

Since the umbilical arteries carry fetal blood to the placenta we studied flow velocity waveforms in these vessels with a simple continuous wave Doppler system to assess placental blood flow. The ratio of peak systolic to least diastolic (A/B) flow velocity was measured as an index of placental flow resistance. In 15 normal pregnancies there was a small but significant decrease in this ratio through the last trimester. The A/B ratio was measured on 436 occasions in 168 high-risk pregnancies. In 32 of 43 fetuses subsequently shown to be small for gestational age there was an increase in placental flow resistance with reduced, absent or even reversed flow in diastole. This finding was also present in the one fetus which died in utero. Serial studies in patients with fetal compromise indicated increasing flow resistance, a reverse of the normal trend. These results were not available to the clinician yet of 24 fetuses born before 32 weeks 13 had a high A/B ratio, and all of them were born electively. Maternal hypertension was associated with an increase in fetal placental flow resistance. The umbilical artery A/B ratio provides a new and non-invasive measure of feto-placental blood flow resistance.     

The use of lidocaine for fetocide in late termination of pregnancy

Objective To assess the use of lidocaine (1%) to induce permanent fetal cardiac asystole for fetocide in late termination of pregnancy.
Design Prospective observational study.
Setting One tertiary referral fetal medicine unit in France.
Sample Fifty patients undergoing termination of pregnancy between 20 and 36 weeks of gestation for severe abnormalities or severe maternal conditions.
Methods Fetocide was performed by umbilical vein puncture under ultrasound guidance with injection of sufentanil (5 μg) followed by 7 to 30 mL of lidocaine (1%).
Main outcome measures Percentage of successful procedures to obtain permanent fetal cardiac asystole and maternal side effects.
Results The procedure was successful in 92% of cases (46/50) with complete cessation of heart activity. The mean amount of lidocaine was 15.3 (6.5) mL. In three cases, fetocide was performed by cardiocentesis and in one case lidocaine was unsuccessful and fetocide was performed with KCl. There were no maternal side effects.
Conclusion Lidocaine is an effective drug to perform fetocide with doses below the toxic dose for the mother.