Redistribution of cardiac output and oxygen delivery in the hypoxemic fetal lamb

Anatomical and functional changes of the fetal adrenal gland in intrauterine growth restriction

OBJECTIVE

The aim of this study was to demonstrate the establishment of adrenal sparing in intrauterine growth restricted (IUGR) human fetuses. IUGR fetuses are a subgroup of small for gestational age (SGA) fetuses that are unable to reach their own growth potential because of chronic hypoxia and undernutrition. We hypothesized that in IUGR fetuses the adrenal gland is relatively larger and secretion of noradrenaline (NA), adrenaline (A), and cortisol is increased.

STUDY DESIGN

This is a prospective observational study including 65 singleton pregnancies (42 IUGR and 23 controls). Using two-dimensional ultrasound, we measured fetal adrenal diameters and adrenal/abdominal circumference (AD/AC) ratio between 25 and 37 weeks. We considered only one measurement per fetus. In 21 pregnancies we also measured NA, A, and cortisol levels in arterial and venous fetal cord blood collected at the time of delivery.

RESULTS

The AD/AC ratio was significantly higher in IUGR fetuses than in controls. Cord NA and A levels were significantly higher in IUGR fetuses than in controls. An increase in cortisol secretion in IUGR fetuses was observed but the difference was not statistically significant.

CONCLUSIONS

Adrenal sparing correlates with a relative increase in adrenal measurements and function.

Association between multi-organ dysfunction and adverse outcome in infants with hypoxic ischemic encephalopathy

OBJECTIVE

To evaluate multi-organ dysfunction (MOD) in newborns treated with therapeutic hypothermia (TH) for hypoxic ischemic encephalopathy (HIE), and to compare MOD in those with normal/mild magnetic resonance imaging (MRI) findings to those with moderate to severe MRI findings or death.

STUDY DESIGN

Retrospective single-center observational study of infants treated with TH. A total of 16 parameters across 7 organ systems were analyzed. Primary outcome was death or moderate to severe brain injury on MRI.

RESULT

Of 157 infants treated with TH, 77% had ≥2 organ systems with dysfunction. The number of organ systems with dysfunction was strongly associated with death or moderate-to-severe brain injury (p < 0.0001). Hematologic (68%) and hepatic (65%) dysfunction were most common. Neurologic and renal dysfunction were most strongly associated with the primary outcome (OR 13.5 [6.1-29.8] and 11.2 [4.1-30.3], respectively), while pulmonary hypertension was not.

CONCLUSION

MOD is prevalent in infants undergoing TH for HIE, and the association between MOD and adverse outcomes may impact clinical care and counseling.

Doppler Ultrasound of the Fetal Descending Aorta: An Objective Tool to Assess Placental Blood Flow Resistance in Pregnancies With Discordant Umbilical Arteries

OBJECTIVES

To determine the relationship between blood flow in the fetal descending aorta and discordant umbilical arteries (UAs).

METHODS

Pulsed wave Doppler of both UAs and the descending aorta was performed at 4-weekly intervals between 14 and 40 weeks of gestation in 209 pregnant women. In datasets with discordant UAs, a linear mixed effects model was used to determine the categorical relationship between the UA pulsatility index (PI) (high, low and average) and the descending aorta PI.

RESULTS

Of the 209 cases, 81 had a discordance of greater than 25% in UA PI during one of their visits. There were no differences in birth outcomes between the groups with concordant and discordant UA PIs. In the cases with discordant UA PIs, the descending aorta PI was most strongly associated with both the average UA PI (P = .008), and with the UA with the lower PI (P = .008).

CONCLUSIONS

The relationship between blood flow in the descending aorta and UAs is consistent with the law for combining resistances in parallel. Measurements of the descending aorta PI, particularly in a scenario with discordant UAs, may inform the stability of the feto-placental circulation where discordant UA PIs are found.

Is Cardiomegaly an Indication of "Heart-Sparing Effect" in Small Fetuses?

INTRODUCTION

This study aimed to test the hypothesis that cardiac size is maintained in small fetuses presenting with cardiomegaly.

MATERIALS AND METHODS

We identified singleton fetuses with estimated fetal weight <10th centile and with cardiomegaly without another more likely cardiac or extra-cardiac cause. We used Z-scores for cardiac and thoracic circumferences normalized for gestational age (GA), biparietal diameter (BPD), head circumference (HC), and femur length (FL), obtained from 188 normally grown fetuses.

RESULTS

When comparing chest size, small fetuses had significantly lower thoracic circumferences median Z-scores (IQR) for GA = -4.82 (-6.15 to -3.51), BPD = -2.42 (-4.04 to -1.48), HC = -2.72 (-4.53 to -1.90), and FL = -1.60 (-2.87 to -0.71); p < 0.001 for all. When comparing heart size, small fetuses showed lower cardiac circumferences median Z-scores (IQR) for GA = -1.59 (-2.79 to -0.16); p < 0.001, similar cardiac circumferences Z-scores for BPD = 0.29 (-0.65 to 1.28); p = 0.284 and HC = 0.11 (-1.13 to 0.96); p = 0.953, and higher cardiac circumferences Z-scores for FL = 0.94 (-0.05 to 2.13); p < 0.001.

CONCLUSIONS

Our results show that in small fetuses with cardiomegaly, the heart maintains normal dimensions when normalized to cranial diameters and higher dimensions when normalized to long bones. This provides insight into cardiac adaptation to adverse intrauterine environment.

Mid-pregnancy fetal growth, uteroplacental Doppler indices and maternal demographic characteristics: role in prediction of stillbirth

INTRODUCTION

To evaluate the relative value of mid trimester fetal growth, uterine artery Doppler indices and maternal demographics in prediction of stillbirth.

MATERIAL AND METHODS

Retrospective cohort study; 23 894 singleton pregnancies routinely scanned between 19 and 24 weeks' gestation. Maternal characteristics included age, body mass index, ethnicity and medical history. Fetal biometry indices, birthweight and uterine artery pulsatility index values were converted to percentiles and multivariable logistic regression analysis was performed. The predictive accuracy was assessed using receiver operating characteristic curves analysis. The main outcome was prediction of preterm and term stillbirths.

RESULTS

Non-Caucasian ethnicity, femur length centile and uterine artery pulsatility index were significantly associated with the risk of stillbirth (all p < 0.01). The detection rate of screening by maternal factors alone was 19% for all stillbirths, and 12 and 14% for term and preterm stillbirth at a 10% false positive rate, respectively. Using femur length centile alone, the detection rates were 27 and 23%, respectively. Uterine artery pulsatility index alone was able to predict 24 and 31% of term and preterm stillbirths. Screening by combining maternal factors, femur length centile and uterine artery Doppler detected 27 and 35% of term and preterm stillbirths at a 10% false positive rate.

CONCLUSIONS

Second trimester ultrasound assessment offers an opportunity to identify pregnancies at the highest risk of stillbirth occurring as a consequence of placental dysfunction. This information may be useful to improve pregnancy outcome by identifying women who may benefit from increased ultrasound surveillance and/or timely intervention.

The cardiovascular response to birth asphyxia is altered by the surrounding environment

BACKGROUND

A sustained bradycardia is used as a major indicator of severe perinatal asphyxia. However, lambs asphyxiated ex utero do not exhibit the same bradycardic response as lambs asphyxiated in utero. It is possible that the local in utero environment may influence the initial cardiovascular response to asphyxia. We assessed the effect of facial immersion in water on the cardiovascular response to birth asphyxia.

METHODS

Pregnant ewes (138±1 days gestation) were anaesthetised and fetuses were exteriorised and instrumented for measurement of cardiopulmonary haemodynamics. The lamb's head either remained in air (n=5) or was placed in water that was either warm (40±1°C; n=5) or at room temperature (21±1°C; n=5) before the umbilical cord was clamped to induce asphyxia.

RESULTS

Heart rate after bradycardia onset was reduced in lambs asphyxiated with their head in cool water (-34±2%) and warm water (-25±4%) compared with those in air (-11±5%; p<0.05). Similarly, the decrease in blood pressure was faster in lambs with water around the face compared with those in air. From 75 s after asphyxia onset, mean and end-diastolic carotid blood flow was higher in the group asphyxiated in air (25±4 mL/kg/min), compared with the groups in water (13±3 mL/kg/min, warm water; 16±2 mL/kg/min, cool water; p<0.05).

CONCLUSIONS

The cardiovascular response to birth asphyxia is altered by the presence and temperature of water surrounding the head. The previous understanding of the vagally mediated bradycardia associated with birth asphyxia may include components of the diving reflex.

Cardiovascular Alterations and Multiorgan Dysfunction After Birth Asphyxia

The cardiovascular response to asphyxia involves redistribution of cardiac output to maintain oxygen delivery to critical organs such as the adrenal gland, heart, and brain, at the expense of other organs such as the gut, kidneys and skin. This redistribution results in reduced perfusion and localized hypoxia/ischemia in these organs, which, if severe, can result in multiorgan failure. Liver injury, coagulopathy, bleeding, thrombocytopenia, renal dysfunction, and pulmonary and gastrointestinal injury all result from hypoxia, underperfusion, or both. Current clinical therapies need to be considered together with therapeutic hypothermia and cardiovascular recovery.

Transcriptomics Modeling of the Late-Gestation Fetal Pituitary Response to Transient Hypoxia

Background

The late-gestation fetal sheep responds to hypoxia with physiological, neuroendocrine, and cellular responses that aid in fetal survival. The response of the fetus to hypoxia represents a coordinated effort to maximize oxygen transfer from the mother and minimize wasteful oxygen consumption by the fetus. While there have been many studies aimed at investigating the coordinated physiological and endocrine responses to hypoxia, and while immunohistochemical or in situ hybridization studies have revealed pathways supporting the endocrine function of the pituitary, there is little known about the coordinated cellular response of the pituitary to the hypoxia.

Results

Thirty min hypoxia (from 17.0±1.7 to 8.0±0.8 mm Hg, followed by 30 min normoxia) upregulated 595 and downregulated 790 genes in fetal pituitary (123–132 days’ gestation; term = 147 days). Network inference of up- and down- regulated genes revealed a high degree of functional relatedness amongst the gene sets. Gene ontology analysis revealed upregulation of cellular metabolic processes (e.g., RNA synthesis, response to estrogens) and downregulation of protein phosphorylation, protein metabolism, and mitosis. Genes found to be at the center of the network of upregulated genes included genes important for purine binding and signaling. At the center of the downregulated network were genes involved in mRNA processing, DNA repair, sumoylation, and vesicular trafficking. Transcription factor analysis revealed that both up- and down-regulated gene sets are enriched for control by several transcription factors (e.g., SP1, MAZ, LEF1, NRF1, ELK1, NFAT, E12, PAX4) but not for HIF-1, which is known to be an important controller of genomic responses to hypoxia.

Conclusions

The multiple analytical approaches used in this study suggests that the acute response to 30 min of transient hypoxia in the late-gestation fetus results in reduced cellular metabolism and a pattern of gene expression that is consistent with cellular oxygen and ATP starvation. In this early time point, we see a vigorous gene response. But, like the hypothalamus, the transcriptomic response is not consistent with mediation by HIF-1. If HIF-1 is a significant controller of gene expression in the fetal pituitary after hypoxia, it must be at a later time.

Impact of cerebral redistribution on neurodevelopmental outcome in small-for-gestational-age or growth-restricted babies: a systematic review

OBJECTIVES

To review systematically the evidence on impact of cerebral redistribution, as assessed by fetal middle cerebral artery (MCA) Doppler, on neurological outcomes in small-for-gestational-age (SGA) or growth-restricted fetuses.

METHODS

For this systematic review, MEDLINE was searched for all controlled studies reporting neurological outcomes in SGA or growth-restricted babies with cerebral redistribution based on MCA Doppler indices, from inception to September 2013. We used relative risk or odds ratios, with 95% CI, to identify the association of cerebral redistribution with neurological outcomes.

RESULTS

The search yielded 1180 possible citations, of which nine studies were included in the review, with a total of 1198 fetuses. Definitions of SGA and cerebral redistribution were variable, as was study quality. Data could not be synthesized in meta-analyses because of heterogeneity in outcome reporting. Cerebral redistribution was not associated with increased risk of intraventricular hemorrhage in neonates (five studies; n = 806). When present in preterm fetuses, cerebral redistribution was associated with normal Neonatal Behavioral Assessment Scale (NBAS) scores at 40 weeks (one study; n = 62) but abnormal psychomotor development at 1 year of age on the Bayley scale (one study; n = 172). When present in term SGA fetuses, cerebral redistribution was associated with increased risk of motor and state organizational problems on NBAS (two studies; n = 158), and lower mean percentile scores in communication and problem solving at 2 years of age on the Ages and Stages Questionnaire (one study; n = 125).

CONCLUSIONS

SGA fetuses with cerebral redistribution may be at higher risk of neurodevelopmental problems. More data are needed from adequately controlled studies with long-term follow-up before conclusions can be drawn. If these findings are true, there is a need to re-evaluate timing of delivery in the management of SGA fetuses, particularly when cerebral redistribution is found at term gestation.

Isolated Short Fetal Femur Length in the Second Trimester and the Association with Adverse Perinatal Outcome: Experiences from a Tertiary Referral Center

Objective

To determine the association between isolated mid-trimester short fetal femur length and adverse perinatal outcome.

Methods

This is a retrospective cohort study of patients with singleton gestations routinely assessed by second trimester ultrasound examination during 2006-2013. A fetal isolated short femur was defined as a femur length (FL) below the 5^th percentile in a fetus with an abdominal circumference greater than the 10^th percentile. Cases of aneuploidy, skeletal dysplasia and major anomalies were excluded. Primary outcomes of interest included the risk of small for gestational age neonates, low birth weight and preterm birth (PTB). Secondary outcome parameters were a 5-min Apgar score less than 7 and a neonatal intensive care unit admission. A control group of 200 fetuses with FL ≥ 5th percentile was used to compare primary and secondary outcome parameters within both groups. Chi-square and Student’s t-tests were used where appropriate.

Results

Out of 608 eligible patients with a short FL, 117 met the inclusion criteria. Isolated short FL was associated with an increased risk for small for gestational age (19.7% versus 8.0%, p = 0.002) neonates, low birth weight (23.9% versus 8.5%, p<0.001), PTB (19.7% versus 6.0%, p<0.001) and neonatal intensive care unit admissions (13.7% versus 3.5%, p = 0.001). The incidence of a 5-min Apgar score less than 7 was similar in both groups.

Conclusion

Isolated short FL is associated with a subsequent delivery of small for gestational age and Low birth weight neonates as well as an increased risk for PTB. This information should be considered when counseling patients after mid-trimester isolated short FL is diagnosed.

Evaluation of utero-placental and fetal hemodynamic parameters throughout gestation in pregnant mice using high-frequency ultrasound

Throughout gestation, changes in maternal and fetal Doppler parameters in pregnant mice, similar to those obtained in human fetuses, were detected using high-frequency ultrasound with a 55-MHz linear probe. In the uterine arteries (UtA), fetal umbilical artery (UA) and fetal ductus venosus (DV) peak systolic velocity increased (UtA, p = 0.04; UA, p = 0.0004; DV, p = 0.02), end-diastolic velocity increased (UtA, p < 0.001; UA, p < 0.0001; DV, p = 0.01) and resistance index decreased (UtA, p = 0.0004; UA, p = 0.0001; DV, p = 0.04) toward the end of pregnancy. In the middle cerebral and carotid arteries, end diastolic velocity increased (p = 0.02 and p < 0.0001) and resistance index decreased (both vessels, p < 0.0001). There was a reduction in the pulsatile pattern in the umbilical vein (p < 0.05). The increased velocities and reduced resistance index suggest a progressive increment in blood flow to the fetal mouse toward the end of pregnancy. Fetal and utero-placental vascular parameters in CD-1 mice can be reliably evaluated using high-frequency ultrasound.

AltitudeOmics: effect of ascent and acclimatization to 5260 m on regional cerebral oxygen delivery

Cerebral hypoxaemia associated with rapid ascent to high altitude can be life threatening; yet, with proper acclimatization, cerebral function can be maintained well enough for humans to thrive. We investigated adjustments in global and regional cerebral oxygen delivery (DO2) as 21 healthy volunteers rapidly ascended and acclimatized to 5260 m. Ultrasound indices of cerebral blood flow in internal carotid and vertebral arteries were measured at sea level, upon arrival at 5260 m (ALT1; atmospheric pressure 409 mmHg) and after 16 days of acclimatization (ALT16). Cerebral DO2 was calculated as the product of arterial oxygen content and flow in each respective artery and summed to estimate global cerebral blood flow. Vascular resistances were calculated as the quotient of mean arterial pressure and respective flows. Global cerebral blood flow increased by ∼70% upon arrival at ALT1 (P < 0.001) and returned to sea-level values at ALT16 as a result of changes in cerebral vascular resistance. A reciprocal pattern in arterial oxygen content maintained global cerebral DO2 throughout acclimatization, although DO2 to the posterior cerebral circulation was increased by ∼25% at ALT1 (P = 0.032). We conclude that cerebral DO2 is well maintained upon acute exposure and acclimatization to hypoxia, particularly in the posterior and inferior regions of the brain associated with vital homeostatic functions. This tight regulation of cerebral DO2 was achieved through integrated adjustments in local vascular resistances to alter cerebral perfusion during both acute and chronic exposure to hypoxia.

Changes in fetal lamb arterial blood gas and acid-base status with advancing gestation

To determine whether there are changes in blood gas and acid-base status with advancing gestation in the fetal lamb, similar to that reported in the human fetus, blood gas, acid-base, and blood metabolite values were measured in 447 control, arterial blood samples from 108 chronically instrumented fetal lambs between 103 and 146 days gestation. With advancing gestation, Po(2), pH, O(2) saturation, and O(2) content fell significantly, while Pco(2) and hemoglobin concentration increased. Blood glucose and lactate concentrations were unchanged, although the lactate level increased with decreasing Po(2), particularly when below ~13 mmHg. Multiple linear regression indicated that increasing fetal number was associated with decreased Po(2) and glucose level and increased pH, HCO(3)(-), base excess, and lactate concentration. Hemoglobin concentration was higher in female than male lambs. Overall, there was a linear relationship between glucose concentration and birth weight. It is concluded that in fetal lambs as in the human fetus, there are changes in blood gas and acid-base status with advancing gestation. This may be due to the decrease in fetal weight-normalized uterine and umbilical blood flows than occurs in these and other species as gestation proceeds. In addition, the reduced birth weight in twin and triplet lambs may be due to hypoglycemia rather than hypoxemia.

Systematic review and meta-analysis of middle cerebral artery Doppler to predict perinatal wellbeing

OBJECTIVE

Identification of the fetus at risk of compromise is crucial to judicious allocation of monitoring resources and use of preventative treatment with the prospect of improving perinatal outcome. The accuracy of middle cerebral artery (MCA) Doppler for prediction of the fetus at risk of compromise of wellbeing is not known. The objective of this systematic review with bivariate meta-analysis was to evaluate the accuracy of middle cerebral artery Doppler for prediction of compromise of fetal/neonatal wellbeing.

STUDY DESIGN

Systematic review and bivariate meta-analysis with searches of Medline, Embase, Cochrane library, Medion (inception to October 2011), hand searching of journal and reference lists, contact with experts. Two reviewers independently selected articles in which the results of middle cerebral artery Doppler were associated with the occurrence of compromise of fetal/neonatal wellbeing. There were no language restrictions applied.

RESULTS

Thirty-five studies, testing 4025 fetuses, met the selection criteria. Data were extracted on study characteristics, quality and results to construct 2×2 tables. Likelihood ratios for positive and negative test results, sensitivity, specificity and their 95% confidence intervals were generated for the different indices and thresholds. Meta-analysis showed low predictive accuracy. For prediction of adverse perinatal outcome and perinatal mortality the results were positive likelihood ratios 2.77 (1.93, 3.96) and 1.36 (1.10, 1.67) and negative likelihood ratios 0.58 (0.48, 0.69) and 0.51 (0.29, 0.89) respectively.

CONCLUSION

Abnormal middle cerebral artery Doppler showed limited predictive accuracy for compromise of fetal/neonatal wellbeing. High quality primary research or individual patient data meta-analysis looking at this test in combination with other tests is required.

The importance of venous Doppler velocimetry for evaluation of intrauterine growth restriction

The management of growth-restricted fetuses requires accurate diagnosis to optimize the timing of delivery. Doppler velocimetry is the only noninvasive method for assessing the fetoplacental hemodynamic status. This review will give a critical overview of the current knowledge on fetal venous blood flow in pregnancies complicated by in-trauterine growth-restricted fetuses. Adaptation of the circulation in intrauterine growth-restricted fetuses is described. Normal and abnormal venous Doppler waveforms are presented. Correlations of abnormal waveforms with the presence of acidemia and perinatal outcomes are emphasized. Limitations of venous Doppler velocimetry for optimizing the time for delivery and the perinatal outcome are also presented.

Reducing intrapartum-related neonatal deaths in low- and middle-income countries-what works?

Each year, 814,000 neonatal deaths and 1.02 million stillbirths result from intrapartum-related causes, such as intrauterine hypoxia. Almost all of these deaths are in low- and middle-income countries, where women frequently lack access to quality perinatal care and may delay care-seeking. Approximately 60 million annual births occur outside of health facilities, and most of these childbirths are without a skilled birth attendant. Conditions that increase the risk of intrauterine hypoxia--such as pre-eclampsia/eclampsia, obstructed labor, and low birth weight--are often more prevalent in low resource settings. Intrapartum-related neonatal deaths can be averted by a range of interventions that prevent intrapartum complications (eg, prevention and management of pre-eclampsia), detect and manage intrapartum problems (eg, monitoring progress of labor with access to emergency obstetrical care), and identify and assist the nonbreathing newborn (eg, stimulation and bag-mask ventilation). Simple, affordable, and effective approaches are available for low-resource settings, including community-based strategies to increase skilled birth attendance, partograph use by frontline health workers linked to emergency obstetrical care services, task shifting to increase access to Cesarean delivery, and simplified neonatal resuscitation training (Helping Babies Breathe(SM)). Coverage of effective interventions is low, however, and many opportunities are missed to provide quality care within existing health systems. In sub-Saharan Africa, recent health services assessments found only 15% of hospitals equipped to provide basic neonatal resuscitation. In the short term, intrapartum-related neonatal deaths can be substantially reduced by improving the quality of services for all childbirths that occur in health facilities, identifying and addressing the missed opportunities to provide effective interventions to those who seek facility-based care. For example, providing neonatal resuscitation for 90% of deliveries currently taking place in health facilities would save more than 93,000 newborn lives each year. Longer-term strategies must address the gaps in coverage of institutional delivery, skilled birth attendance, and quality by strengthening health systems, increasing demand for care, and improving community-based services. Both short- and long-term strategies to reduce intrapartum-related mortality should focus on reducing inequities in coverage and quality of obstetrical and perinatal care.

Factors associated with small head circumference at birth among infants born before the 28th week

OBJECTIVE

We sought to identify risk factors for congenital microcephaly in extremely low gestational age newborns.

STUDY DESIGN

Demographic, clinical, and placental characteristics of 1445 infants born before the 28th week were gathered and evaluated for their relationship with congenital microcephaly.

RESULTS

Almost 10% of newborns (n = 138), rather than the expected 2.2%, had microcephaly defined as a head circumference >2 SD below the median. In multivariable models, microcephaly was associated with nonwhite race, severe intrauterine growth restriction, delivery for preeclampsia, placental infarction, and being female. The risk factors for a head circumference between <1 and >2 SD below the median were similar to those of microcephaly.

CONCLUSION

Characteristics associated with fetal growth restriction and preeclampsia are among the strongest correlates of microcephaly among children born at extremely low gestational ages. The elevated risk of a small head among nonwhites and females might reflect the lack of appropriate head circumference standards.

Systemic and cerebral hemodynamics during the transitional period after premature birth

Little is known about the effect on clinically relevant outcomes of the complex hemodynamic changes occurring during adaptation to extrauterine life in preterm neonates, particularly in very low birth weight neonates. As cardiovascular adaptation in this extremely vulnerable patient population is complicated by immaturity of all organ systems, especially that of the cardiorespiratory, central nervous, and endocrine systems, maladaptation has been suspected, but not necessarily proven, to contribute to mortality and long-term morbidities. This article describes recent advances in the understanding of hemodynamic changes in very low birth weight neonates during postnatal transition, and reviews the complex and developmentally regulated interaction between systemic and cerebral hemodynamics and the effect of this interaction on clinically relevant outcomes.

Maternal and fetal near-term sheep cytokine responses to carbon dioxide pneumoperitoneum

It is known that carbon dioxide (CO2) pneumoperitoneum induces fetal acidosis in pregnant ewes. Our aim was to determine changes of the levels of maternal and fetal cytokines interleukin-6, interleukin-8, and tumor necrosis factor alpha after CO2 pneumoperitoneum in pregnant ewes. Eight ewes with singleton pregnancies of 120 to 140 days gestation were anesthetized and intubated. Insufflation produced modest but significant maternal arterial hypercapnia (an increase of 10.7 mm Hg; P<0.001) and acidosis (a decrease in mean pH of 0.1.04; P=0.0005). Fetal pCO2 was increased by 15.3 mm Hg on average and pH was decreased by 0.11 U on average immediately after desufflation (both P<0.001). No significant difference was observed in the concentration of cytokine in the maternal or fetal blood samples. These results suggest that respiratory acidosis does not lead to the elevation of cytokines in pregnant ewes and fetuses, which may contribute to premature labor.

What is spared by fetal brain-sparing? Fetal circulatory redistribution and behavioral problems in the general population

Intrauterine growth restriction has been linked to infant behavioral problems. While typically only birth weight is examined, here the authors assessed fetal circulatory redistribution, also called the "brain-sparing effect," which is a fetal adaptive reaction to placental insufficiency. They aimed to investigate whether fetal circulatory redistribution protects against behavioral problems. Within the Generation R Study (Rotterdam, the Netherlands, 2003-2007), fetal circulation variables for the umbilical artery and the middle and anterior cerebral arteries were assessed with Doppler ultrasound in late pregnancy. Ratios between placental resistance and cerebral resistance were related to behavioral problems, as measured by the Child Behavior Checklist, in 935 toddlers aged 18 months. The umbilical/anterior cerebral ratio was associated with the Total Problems summary score from the Child Behavior Checklist (per standard-deviation increase, odds ratio = 1.2, 95% confidence interval: 1.0, 1.5). Children with higher umbilical/anterior cerebral ratios had higher risks of internalizing problems, emotional reactivity, somatic complaints, and attention problems. A high umbilical/middle cerebral ratio was related to higher scores on the Internalizing and Somatic Complaints scales. The authors conclude that infants with circulatory redistribution in gestation are more likely to have behavioral problems. This suggests that "brain-sparing" does not completely spare the brain and indicates underlying pathology with consequences for later behavior.

Association of isolated short femur in the mid-trimester fetus with perinatal outcome

OBJECTIVES

To evaluate the prevalence of fetal isolated short femur in a cohort of women screened for Down syndrome by the integrated test, and to compare the outcome of fetuses with isolated short femur in the mid-trimester with that of fetuses with normal femur length (controls).

METHODS

This was a retrospective cohort study of 1262 women booked for antenatal care and delivery at University College London Hospital. All women had integrated testing in the late first and early second trimesters and a detailed anomaly scan in the mid-trimester. All scan reports, screening results and neonatal data were analyzed statistically.

RESULTS

The fetal femur was short (< 5(th) percentile) in 5.1% of patients and 4.7% had isolated short femur. In pregnancies with isolated short femur, the birth weight was significantly lower and there were higher rates of small-for-gestational age (SGA) and low birth weight (LBW) infants, compared with controls (P < 0.01). The odds ratios for SGA and LBW in pregnancies with isolated short femur were 3.0 (95% CI, 1.5-5.9) and 2.60 (95% CI, 1.1-6.2), respectively. Isolated short femur was associated significantly with low levels of pregnancy-associated plasma protein-A (P = 0.001).

CONCLUSIONS

Isolated short femur in the mid-trimester fetus is associated with fetal growth restriction and SGA. In the context of normal Down syndrome screening and a normal anomaly scan, this marker should be regarded as a predictor for SGA, and fetal growth should be monitored during these pregnancies.

Development and mechanisms of fetal hypoxia in severe fetal growth restriction

Severe fetal growth restriction (FGR) is often associated with hypoxia. We studied FGR hypoxia in an experimental model which is produced by exposing pregnant ewes to a hyperthermic environment. The study utilized simultaneous measurements of several relevant factors, e.g., uterine and umbilical blood flows and O(2) uptakes. Sixteen ewes were divided equally into control (C) and hyperthermic (HT) groups. Hyperthermia (40 degrees C for 12h/35 degrees C for 12h; approximately 35% relative humidity, RH) was maintained for 80 days commencing at approximately 38 days gestational age (dGA term 147+/-3 days). All ewes were then placed in a control environment ( approximately 21 degrees C, 24h; approximately 30% RH) and studied at approximately 134 dGA. Mean HT placental and fetal weights were 39% and 45% of C, respectively (p<0.0001), umbilical O(2) uptake/kg fetus was 76% of C (p<0.01) and umbilical venous PO(2) was reduced (20.2 vs. 29.7 Torr, p<0.001). Contrary to the hypothesis that FGR hypoxia is due to maternal placental hypoperfusion, uterine flow was not reduced in relation to O(2) uptake. The uterine-umbilical venous PO(2) difference was enlarged (38 vs. 23 Torr, p<0.0001). This difference is the expression of a balance between developmental changes in placental structure and oxidative metabolism, which have opposite effects in terms of fetal oxygenation. We postulate that FGR hypoxia results from disproportionate underdevelopment of those changes which allow for a progressive increase in umbilical O(2) uptake.

Fetal and maternal Doppler velocimetry and cytokines in high-risk pregnancy

OBJECTIVE

Fetal hypoxia and preterm delivery are reported to be strongly associated with brain damage and neurodevelopmental delay. Doppler signs of fetal brain sparing have been described during chronic hypoxia, but whether they are related to brain damage is unknown. The aim of this study was to evaluate if markers of tissue injury, i.e., tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) are related to signs of increased perinatal vascular impedance and/or fetal brain sparing in high-risk pregnancies.

STUDY DESIGN

TNF-alpha and IL-6 levels were evaluated in maternal blood serum of 67 high-risk pregnancies. Serum samples were taken at the time of umbilical, middle cerebral artery and uterine artery Doppler velocimetry examination. The values for TNF-a and IL-6 were correlated with reference median values obtained with gestational age in the form of a Z-score.

RESULTS

TNF-alpha levels showed values within the normal range in only four cases. IL-6 values were found normal in 14 cases. The Z-score for mean middle cerebral artery pulsatility index (PI) showed a significant correlation to TNF-alpha and IL-6 levels, P < 0.0001 and P < 0.003, respectively. This might suggest a strong correlation between signs of fetal brain sparing and increased maternal serum TNF-alpha and IL-6 levels. Abnormal uterine artery PI and the presence of a "notch" were also highly significantly related to TNF-alpha and IL-6 levels, which were nearly two-fold higher compared to normal uterine artery blood flow and the absence of a "notch". Abnormal cerebro/placental ratios showed significant correlations to TNF-alpha and IL-6 levels.

CONCLUSION

The present results suggest a strong correlation between levels of TNF-alpha and IL-6 not only for signs of fetal brain sparing, but also for uteroplacental blood flow. This finding supports the role of tissue injury in cases of fetal brain sparing, but whether this is a reflection of brain damage or secondary to placental pathology needs further evaluation.

Computer analysis of three-dimensional power angiography images of foetal cerebral, lung and placental circulation in normal and high-risk pregnancy

Three-dimensional (3-D) ultrasound (US) has greatly improved evaluation of organ circulation. The aim of this study was to explore the possible use of this new technique in normal and high-risk pregnancies. Fetal brain, lung and placenta 3-D power Doppler signal intensity were recorded in 115 normal singleton pregnancies (24 to 42 weeks gestation) and in 67 high-risk pregnancies. Mean image pixel signal intensity was calculated for each organ and a brain-lung ratio. In normal pregnancy, placental and lung signal intensity increased until 33, with a rapid decrease after 38, weeks of gestation. Fetal cerebral signal intensity increased with gestational age. Placental and fetal lung signal intensity was significantly lower in high-risk pregnancies than in the control group, with increased fetal brain and brain-lung ratios. The present results suggest a reduction of placental perfusion after 38 weeks of gestation in normal pregnancy, with redistribution of fetal circulation. Lung signal intensity increased abruptly at 32 weeks of gestation, which might reflect lung maturity. The new method showed signs of centralization of fetal circulation at the end of gestation. The results might suggest a possible clinical use for fetal surveillance in high-risk pregnancies.

Multiorgan dysfunction in infants with post-asphyxial hypoxic-ischaemic encephalopathy

BACKGROUND

Multiorgan dysfunction (MOD) is one of four consensus based criteria for the diagnosis of intrapartum asphyxia. The theoretical concept behind MOD is the diving reflex (conservation of blood flow to vital organs at the cost of non-vital organs).

OBJECTIVES

To assess the patterns of involvement of each major organ/system and combinations of involvement in infants with post-asphyxial hypoxic-ischaemic encephalopathy (HIE), and to describe this in relation to long term outcome.

DESIGN

Retrospective cohort study.

SETTING

Regional tertiary neonatal intensive care unit at the Hospital for Sick Children, Toronto, Canada.

PATIENTS

Term neonates with post-intrapartal asphyxial HIE assessed for kidney, cardiovascular system, lung, and liver function.

OUTCOME

Death and presence or absence of severe neurodevelopmental disability.

RESULTS

Out of 130 of 144 eligible infants with outcome data, 80 (62%) had severe adverse outcome and 50 (38%) had good outcome. All infants had evidence of MOD (at least one organ dysfunction in addition to HIE). Renal, cardiovascular, pulmonary, and hepatic dysfunction was present in 58-88% of infants with good outcome and 64-86% of infants with adverse outcome.

CONCLUSIONS

MOD was present in all the infants with severe post-asphyxial HIE. However, there was no association between MOD and outcome in these infants. No relation between individual or combinations of organ involvements and long term outcomes was observed.

Effects of chronic hypoxia on fetal coronary responses

This review examines the effect of high altitude and/or chronic hypoxia on cardiac mechanisms that influence perfusion of the fetal heart (e.g., tissue metabolism, coronary vessel growth, and coronary blood flow and vessel responsiveness). In response to intrauterine hypoxia, the fetal heart may either reduce its energy demand or increase its substrate and oxygen delivery as a means of sustaining cardiac function. Cardiac glycolysis predominates as a metabolic pathway of ATP synthesis in the fetal heart under both normoxic and hypoxic conditions. During prolonged oxygen insufficiency, normal cardiac function is sustained by anaerobic glycolysis relying primarily on high levels of stored glycogen in the heart. Chronic hypoxia increases coronary vessel growth and myocardial vascularization in fetal hearts, although the response may depend on the presence of ventricular hypertrophy. Recent studies demonstrate that high altitude hypoxia increases both resting fetal coronary flow and coronary flow reserve as an adaptive response toward increasing oxygen delivery. Hypoxia may also directly effect local vascular smooth muscle mechanisms, resulting in altered coronary artery reactivity to circulating vasoactive substances and contributing to enhanced perfusion. Further study is needed to understand the relative importance of each of these cardiac adaptations in contributing to fetal survival. It is likely that differences in fetal coronary responses to intrauterine hypoxia are highly dependent on the gestational age and relative maturity of the animal species.

Fetal superior mesenteric artery blood flow velocimetry in normal and high-risk pregnancy

THE AIM

To record blood flow velocimetry in the fetal superior mesenteric artery in normal pregnancy and to evaluate if blood flow recordings in the vessel might predict adverse outcome in high-risk pregnancy.

METHODS

The fetal superior mesenteric artery blood velocimetry was recorded in a cross sectional manner in 75 normal pregnancies between 27 and 41 weeks of gestation. Reference curves were performed for pulsatility and resistance indices. The superior mesenteric artery was also located in 48 singleton pregnancies complicated by pregnancy-induced hypertension and/or intra-uterine growth retardation. Middle cerebral artery, umbilical artery and vein and uterine artery velocimetry were also recorded.

RESULTS

Superior mesenteric artery PI and RI values expressed an increase in resistance to blood flow with gestational age after 32 weeks of gestation. In all except eight high-risk pregnancies the fetal mesenteric artery PI values were within normal range. Among the pregnancies with absent or reversed blood flow in the umbilical artery, all had abnormal mesenteric artery pulsatility index (PI) (> 97.5th percentiles), one fetus died intrauterine and two others died after delivery due to prematurity, growth retardation and necrotizing enterocolitis. In the remaining fetuses with increased mesenteric artery PI, necrotizing enterocolitis was diagnosed in three cases.

CONCLUSIONS

Increased vascular resistance in the mesenteric artery might be a late sign of fetal circulation redistribution and frequently related to necrotizing enterocolitis in the newborn.

Blood redistribution in the fetal brain during chronic hypoxia

BACKGROUND

Studies on blood flow velocity in the fetal middle cerebral artery have revealed signs of brain sparing in chronic hypoxia. These signs of brain sparing can disappear in the terminal case, but whether this applies to the whole brain or only parts of it is unknown.

METHODS

Velocity waveforms of the middle cerebral, anterior cerebral and posterior cerebral arteries were recorded in 221 pregnancies complicated by pregnancy-induced hypertension. The presence of brain sparing (pulsatility index < 2 standard deviations) was noted and correlated to outcome of pregnancy, including emergency operative intervention and/or neonatal distress.

RESULTS

Signs of brain sparing in the anterior cerebral artery were found in 90 fetuses, and in the middle cerebral and posterior cerebral arteries in 52 and 65, respectively. Signs of brain sparing in the anterior cerebral artery showed the strongest relationship to adverse perinatal outcome. The anterior cerebral artery was the only vessel in which signs of brain sparing were predictive of perinatal mortality.

CONCLUSIONS

Velocimetry of the anterior cerebral artery appears to be superior to that of the middle cerebral and posterior cerebral arteries as a means to predict adverse perinatal outcome. Anterior cerebral artery brain sparing may therefore be less transitory than sparing in the middle cerebral and posterior cerebral arteries, possibly suggesting that the frontal lobes are spared longer than the lateral and occipital regions of the fetal brain.

Fetal cerebral and peripheral circulatory responses to hypoxia after nitric oxide synthase inhibition

The increase in cerebral blood flow (CBF) during hypoxia in fetal sheep at 0.6 gestation is less than the increase at 0.9 gestation when normalized for differences in baseline CBF and oxygen consumption. Nitric oxide (NO) synthase (NOS) catalytic activity increases threefold during this period of development. We tested the hypothesis that administration of the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) decreases the CBF response to systemic hypoxia selectively at 0.9 gestation. We also tested whether any peripheral vasoconstriction during hypoxia is potentiated by L-NAME at 0.9 gestation. Administration of L-NAME increased arterial blood pressure and decreased microsphere-determined CBF during normoxia in fetal sheep at both 0.6 and 0.9 gestation. With subsequent reduction of arterial oxygen content by approximately 50%, the percent increase in forebrain CBF in a control group (57 +/- 11%; +/- SE) and L-NAME-treated group (51 +/- 6%) was similar at 0.6 gestation. Likewise, at 0.9 gestation, the increase in CBF was similar in control (90 +/- 25%) and L-NAME (80 +/- 28%) groups. At 0.9 gestation, L-NAME treatment attenuated the increase in coronary blood flow and increased gastrointestinal vascular resistance during hypoxia. We conclude that NO exerts a basal vasodilatory influence in brain as early as 0.6 gestation in fetal sheep but is not an important mechanism for hypoxic vasodilation in brain at either 0.6 or 0.9 gestation. Thus the developmental increase in NOS catalytic capacity does not appear to be responsible for developmental increases in the CBF response to hypoxia during this period. In contrast, NO modulates the vascular response to hypoxia in heart and gastrointestinal tract.

Fetal adrenal and middle cerebral artery Doppler velocimetry in high-risk pregnancy

OBJECTIVES

Animal studies have shown that hypoxic fetuses redistribute their blood flow, giving preferential supply to the brain, heart and adrenal glands. The aim of this study was to establish whether blood velocity waveforms in the human fetal adrenal artery and middle cerebral artery showed signs of redistribution of fetal circulation in high-risk pregnancy, and to analyze the relationship between signs of such redistribution and the outcome of pregnancy.

METHODS

Fetal middle adrenal artery and middle cerebral artery waveforms were recorded between 27 and 41 weeks of gestation in 102 pregnancies complicated by pregnancy-induced hypertension. Signs of fetal adrenal-sparing were deemed present when the pulsatility index (PI) fell below the fifth percentile of the normal range. Signs of fetal brain-sparing were deemed present when the cerebral artery PI was below the mean -2 SD of the normal range and the cerebroplacental PI ratio was < 1.08.

RESULTS

Signs of adrenal sparing were found in 64 cases and brain sparing in 32 cases. Fetal adrenal sparing was strongly associated with adverse perinatal outcome; all perinatal mortality cases showed signs of adrenal sparing. There was a significant positive correlation between the fetal adrenal artery PI and umbilical arterial and venous pH.

CONCLUSIONS

Signs of adrenal sparing are frequent in high-risk pregnancies. Adrenal artery velocimetry may be a useful procedure for fetuses at risk for hypoxemia.

The pulmonary vein Doppler flow velocity waveform: feature analysis by comparison of in vivo pressures and flows with those in a computerized fetal physiological model

OBJECTIVES

Doppler flow velocity waveforms (FVW) in fetal veins that discharge into the atria show fluctuations related to atrial events. Pulmonary veins are of particular interest because both ends (atrial and collecting venule) are within the intrathoracic pressure environment reducing fetal breathing artifacts. Indices, such as pulsatility index for veins (PIV), have been suggested to classify FVWs and relate them to fetal well being. We wished to examine the relationship between function and FVW in circumstances which cannot ethically be examined in vivo, by studying the mechanisms which produced altered 'flows' in a detailed fetal computer model. We then related these findings to current flow indices.

METHODS

A computer model of the feto-placental unit, responding to changes in organ oxygenation and regional flow is briefly described. In vivo intracardiac pressures and FVWs obtained from other studies were used to extend detail in the model until matching 'pressures' and 'flows' resulted. The effects of flow redistribution in the hypoxic fetus on pulmonary vein 'Doppler' flow velocity waveforms were then studied.

RESULTS AND CONCLUSIONS

Flow reversal in pulmonary veins during atrial contraction indicates hypoxia, but change of shape of the FVW envelope reflects the changes in the pressure waveform of the left atrium. Of the major veins the pulmonary vein Doppler FVW gave the truest representation of atrial pressure response to both intracardiac and systemic vascular status. Although current indices indicate general fetal condition, more specific indices are needed if pulmonary venous flow is to be used as an end-point. A pulmonary vein pressure gradient index is suggested.

Nonstress testing and contraction stress testing

Antepartum fetal heart rate (FHR) testing, including the nonstress test and contraction stress test, has evolved in clinical usage over the past 3 decades. Although the nonstress test has become a standard of care in high-risk pregnancy, it has been modified by the use of fetal stimulation (vibroacoustic stimulation) and the addition of automated fetal movement recording (actocardiotocography). In all of its formats, antepartum FHR testing has been associated with reduction of preventable fetal loss. More recently, there have been attempts to improve test efficacy by computer-enhanced approaches.

Relationship between flow through the fetal aortic isthmus and cerebral oxygenation during acute placental circulatory insufficiency in ovine fetuses

OBJECTIVE

We sought to investigate whether the reversal of blood flow through the aortic isthmus, as observed during an increase in placental vascular resistance, could be responsible for a significant fall in oxygen delivered to the fetal brain.

STUDY DESIGN

With the appearance of reverse flow in the aortic isthmus, preplacental blood with low oxygen saturation could contaminate the ascending aorta blood destined for the brain. Stepwise compression of the umbilical veins of 8 exteriorized fetal lambs was realized at approximately 140 days of gestation. Four other animals were used as controls. Flows through the aortic isthmus and both carotid and umbilical arteries were measured by Doppler echocardiography in the basal state (hemodynamic class 1) and during moderate (class 2), severe (class 3), and extreme (class 4) increases in resistance to placental flow. Oxygen delivered to the brain was calculated from carotid blood flow and oxygen content.

RESULTS

In the control group no change was noted in umbilical and carotid arteries or in the aortic isthmus blood flow. Oxygen delivered to the brain remained stable. In the study group the increase in resistance to placental flow caused a significant fall in umbilical flow and carotid oxygen content, while blood flow in the carotid arteries increased slightly. The values for aortic isthmus flow and oxygen delivered to the brain during the 4 hemodynamic classes were, on average, as follows: class 1, 98.2 and 2.9 mL/(min x kg); class 2, 52.8 and 3.1 mL/(min x kg); class 3, 3.7 and 2.6 mL/(min x kg); and class 4, -29.8 and 0.7 mL/(min x kg), respectively.

CONCLUSION

During an acute increase in placental vascular resistance, delivery of oxygen to the brain is preserved despite a significant drop in arterial oxygen content as long as net flow through the isthmus is anterograde.

The application of individualised fetal growth curves

Individually adjusted or 'customised' growth charts aim to optimise the assessment of fetal growth by taking individual variation into account, and by projecting an optimal curve which delineates the potential weight gain in each pregnancy. This results in an increased detection rate of true growth restriction and a reduction in false positive diagnoses for IUGR. An adjustable standard can apply across geographical boundaries, as individual variation exceeds that between different maternity populations.

Cerebral Doppler blood flow velocimetry and central hemodynamics in the ovine fetus during hypoxemia-acidemia

The purpose of this study was to assess the effects of hypocapnic hypoxia, acidemia and the combination of hypoxia/acidemia on blood flow velocity variables in the fetal cerebral circulation. Chronically instrumented fetal sheep were used and the ewes were induced to breathe a hypoxic gas mixture for about 90 min. This caused an initial period of hypoxemia followed by a period of mixed hypoxemia/acidemia. When the ewe was reoxygenated, the fetus experienced a period of normoxic acidemia. The fetal cerebral circulation was assessed by recording Doppler blood flow velocity waveform variables in a cerebral vessel and the umbilical artery, using standard ultrasound equipment. External carotid artery blood flow was maintained during hypoxic and hypoxic/acidotic periods despite a fall in cardiac output. In the cerebral vessel, mean maximum velocity (time-averaged maximum velocity), minimum diastolic velocity and maximum systolic velocity manifested increases during hypoxic and hypoxic-acidotic periods, but pulsatility index did not change due to the effect of reduced heart rate on pulsatility index. Umbilical artery pulsatility index increased in the hypoxic and hypoxic-acidotic periods, despite unchanged mean maximum velocity, minimum diastolic velocity and maximum systolic velocity. With acute hemodynamic changes, the measurement of pulsatility index can yield misleading results. For clinical and experimental research on the fetal cerebral circulation, more attention should be paid to the individual Doppler variables, especially to the mean maximum velocity, than to the pulsatility index alone. Changes in mean maximum velocity recorded from the cerebral artery seem to reflect changes in the cerebral arterial flow.

Metabolic and circulatory adaptations to chronic hypoxia in the fetus

When oxygenation is compromised the fetus is capable of a number of adaptive responses, both protective and potentially pathologic, which can be categorized as those affecting fetal metabolism and those affecting fetal oxygen transport. However, both the extent and the duration of the impairment in oxygenation will bear on these adaptive responses. While fetal O2 extraction is increased when oxygenation is acutely compromised thus maintaining O2 consumption, with chronic hypoxemia there is a decrease in O2 consumption paralleling that in O2 delivery and contributed to by the resultant fall-off in growth and alterations in behavioural activity. While a redistribution of blood flow to vital organs continues to be evident, this will be less pronounced than that seen with acute hypoxemia reflecting diminished hormonal changes, underlying metabolic alterations, and the extent to which fetal blood gases are normalized. Much of this information is based on experimental data using unanesthetized fetal sheep with chronic catheterization; however, clinical outcome data and the use of investigative techniques including ultrasound scanning and cordocentesis have supported the relevance of this experimental data to the human situation.

Regional blood flow and the endocrine response to sustained hypoxemia in the preterm ovine fetus

To determine the circulatory response of the preterm fetus to a sustained hypoxic insult, regional blood flow was measured (microsphere technique) in 12 unanesthetized fetal sheep (0.75 gestation) during a normoxic control period, after 1 h and 8 h of sustained hypoxemia, and after a 1-h recovery period. Associated endocrine changes which might relate to organ-specific changes in blood flow were also assessed. Myocardial and cerebral blood flow were increased by 240 and 90%, respectively, such that oxygen delivery to the heart was well maintained throughout the study, whereas that to the brain was significantly decreased by 8 h of hypoxic study. Regional blood flows for all structures within the brain showed similar percent increases, except that for the pituitary gland, where the increase was much smaller, and that for the choroid plexus, where blood flow actually fell. Whereas blood flow to upper body muscle showed no significant change throughout the study, that to the thyroid was increased by 70% by 1 h of hypoxic study but fell thereafter. Adrenal cortical blood flow relative to that of the medulla was increased 3-fold by 8 h of hypoxic study, indicating a differential effect of sustained hypoxia on these vascular beds. Although pituitary and thyroid blood flows showed no relationship to respective trophic and/or secretory hormones measured, values for adrenal cortical flow relative to medullary flow were well correlated with plasma concentrations of ACTH. It is concluded that the "centralization" of blood flow to vital organs in response to a sustained hypoxic insult is qualitatively similar for both the preterm and near term ovine fetus and that hypoxic regulatory mechanisms may be better protective of the heart. Additionally, a role for the functional activation of the adrenal gland in its blood flow response to sustained hypoxemia is suggested.

Continuous central venous oxygen saturation (ScvO2) measurement using a fibre optic catheter in newborn infants

AIMS

To describe the range of central venous oxygen saturation (ScvO2) values in stable newborn infants breathing room air; to examine the correlation between ScvO2 and arterial oxygen saturation (SaO2); to describe fractional oxygen extraction; and the shunt index, an estimate of the venous admixture.

METHODS

A prospective clinical observational study was made of 10 preterm infants breathing room air after the acute phase of respiratory distress syndrome, and with an umbilical venous catheter in situ. A fibre optic catheter remained in the right atrium for continuous measurement of oxygen saturation.

RESULTS

ScvO2, SaO2, blood pressure and heart rate were registered every 15 minutes. Fractional oxygen extraction and shunt index were calculated. SaO2 and ScvO2 were 93.4 (SD 3.7)% and 73.56 (5.25)%, respectively. In seven patients ScvO2 values correlated significantly with SaO2. Fractional oxygen extraction was 0.21 (0.04) and was significantly correlated with ScvO2. The shunt index was 24% (12) and was significantly correlated with SaO2.

CONCLUSIONS

Stable preterm infants breathing room air had an ScvO2 ranging from 65% to 82% (5th and 95th percentile), which corresponded to SaO2 > or = 86%. ScvO2 values were significantly correlated with SaO2 in most patients.

Transmission pulse oximetry in the fetal lamb: is there a universal calibration?

Transmission pulse oximetry is widely used for oxygen monitoring. The use of pulse oximeters is steadily expanding toward situations with low arterial oxygen saturation (Sao2) values. Therefore, we evaluated transmission pulse oximetry in the unanesthetized fetal lamb at low Sao2 levels. In seven fetal lambs, fetal hypoxemia was induced by occlusion of the maternal common iliac artery, four days after the instrumentation of the animal. Two Nellcor prototype transmission Y-sensors (light emitting diodes: 660 and 890 nm) were applied, one around a forelimb muscle and one around a skinfold in the neck, and were connected to Nellcor pulse oximeters. The pulse oximeter was calibrated for the skin measurements. Pulse oximeter saturation readings (Spo2) were compared with sample Sao2 values, over an Sao2 range of 13 to 63%. For the neck sensor the SD of the difference was 5.0% (n = 101). For the muscle sensor the mean difference was 19.5% and the SD of the difference was 5.9% (n = 206). Regression analysis showed a different calibration line for the muscle sensor with the equation: Spo2 = 0.92 x Sao2 + 21.90. Continuous recordings were obtained both from the forelimb muscle and from the neck, but the recordings from the neck showed a substantial loss of signal during the hypoxemia period. We conclude that transmission pulse oximetry is less accurate below an Sao2 of 70% in fetal lambs than above 70% Sao2. At these low levels of Sao2, pulse oximeters may need to be constructed with different calibration lines for various application positions of the body.

Maternal risk factors in fetal alcohol syndrome: provocative and permissive influences

We present an hypothesis integrating epidemiological, clinical case, and basic biomedical research to explain why only relatively few women who drink alcohol during pregnancy give birth to children with alcohol-related birth defects (ARBDs), in particular, Fetal Alcohol Syndrome (FAS). We argue that specific sociobehavioral risk factors, e.g., low socioeconomic status, are permissive for FAS in that they provide the context for increased vulnerability. We illustrate how these permissive factors are related to biological factors, e.g., decreased antioxidant status, which in conjunction with alcohol, provoke FAS/ARBDs in vulnerable fetuses. We propose an integrative heuristic model hypothesizing that these permissive and provocative factors increase the likelihood of FAS/ARBDs because they potentiate two related mechanisms of alcohol-induced teratogenesis, specifically, maternal/fetal hypoxia and free radical formation.

Do concepts of causes and prevention of cerebral palsy require revision?

OBJECTIVE

My purpose was to explore the criteria of The American College of Obstetricians and Gynecologists (Technical Bulletin No. 163) for perinatal asphyxia to be linked to subsequent cerebral palsy.

STUDY DESIGN

Analysis of four cases of intrapartum fetal insults with subsequent cerebral palsy and a literature review are presented.

RESULTS

All of the four cerebral palsy cases had sufficient intrapartum causes of cerebral palsy, yet none fulfilled The American College of Obstetricians and Gynecologists' linkage criteria. Complications in the cerebral palsy cases were as follows: maternal intrapartum cardiac arrest, fetal skull fracture with brain infarct, intrapartum fetal stroke, and a newborn delivered after uterine rupture with only central nervous system defects. There are no well-done laboratory or clinical studies that unequivocally support the "criteria" that umbilical artery pH must be < 7.00 or the requirements of Apgar score < 3, hypoxic-ischemic encephalopathy, and multiple organ dysfunction. Apparent exceptions to these criteria occur.

CONCLUSIONS

The American College of Obstetricians and Gynecologists Technical Bulletin's criteria for cerebral palsy linkage and the role of parturition in cerebral palsy should be reevaluated. A rebirth of obstetric enthusiasm for cerebral palsy research, teaching, and treatment needs to occur.

The ductus arteriosus, pre- and post-ductal oxygen saturation measurements in fetal lambs

In the fetus, the arterial oxygen saturation (SaO2) in the ascending aorta is higher than in the descending aorta. We questioned whether this difference over the ductus arteriosus (delta SaO2) would change during hypoxaemia. Therefore, six chronically instrumented fetal lambs (119-126 days of gestation) were studied, by changing the inspired oxygen (FIO2) via a tracheal tube to the ewe. The SaO2 was measured intermittently every 15 min with blood samples obtained from the ascending and descending aorta, and continuously with 2 pulse oximeters at both sides of the ductus arteriosus. delta SaO2 was at a level of 3.4-5.3% and had a tendency to decrease at preductal SaO2 levels of 10-20% and at pH levels below 7.25. The precision of the pulse oximeters, expressed as standard deviation of the differences between sample SaO2 and pulse oximeter SaO2, was around 5.0% for the individual calibration curves. This precision was not enough to show details of the course of delta SaO2 between the blood samples. Our results show that there is no change in delta SaO2 across the ductus arteriosus.

Fetal cerebral Doppler in the recognition of fetal compromise

OBJECTIVE

To establish reference ranges for the human fetal middle cerebral artery pulsatility index (MCA PI) for the local obstetric population, and to compare computerised antenatal fetal heart rate (FHR) analysis with the MCA PI as indicators of fetal compromise.

DESIGN

Prospective data collection for selected patients.

SETTING

High risk pregnancy unit of a teaching hospital.

SUBJECTS

Group 1 consisted of 18 healthy women with uncomplicated singleton pregnancies. Group 2 consisted of 27 women admitted to the high risk pregnancy unit over a 9 month period with intrauterine growth retardation and other related problems; all these women were delivered by prelabour caesarean section.

INTERVENTION

Serial Duplex sonography to determine fetal MCA PI in Groups 1 and 2. Serial FHR analysis using computerised numerical techniques in Group 2 only.

MAIN OUTCOME MEASURES

Serial MCA PI values from 24 to 39 completed weeks of gestation in Group 1. Comparison of serial MCA PI values with FHR analysis in relation to fetal outcome in Group 2.

RESULTS

In Group 1 the MCA PI diminished significantly as gestation advanced from 1.73 (SD 0.25) at 24 weeks to 1.38 (SD 0.26) at 39 weeks (P < 0.01). In Group 2 eleven babies were hypoxaemic at delivery: all had low MCA PI values while only nine had an abnormal FHR prior to delivery.

CONCLUSION

In normal pregnancy, there is a fall in the fetal MCA PI with advancing gestation which probably reflects a decreasing vascular resistance to fetal cerebral blood flow. Hypoxaemia at delivery appeared to be better recognised by the fetal MCA flow velocity waveform than the FHR analysis. This increased sensitivity, however, was achieved at the expense of a reduced specificity. Larger studies are needed to confirm the findings of this preliminary investigation.

Effects of maternal administration of 3% carbon dioxide on umbilical artery and fetal renal and middle cerebral artery Doppler waveforms

OBJECTIVE

The null hypothesis is that umbilical, middle cerebral, and renal artery pulsed Doppler velocity waveforms in the normal term fetus may be affected during short-term maternal inhalation of 3% carbon dioxide gas mixture.

STUDY DESIGN

Seventy-two observations were made on 14 term fetuses before and during maternal 3% carbon dioxide gas mixture inhalation. The umbilical, middle cerebral, and renal arteries of these fetuses were sampled with pulsed Doppler velocity waveforms and recorded on a strip chart at a preset speed of 50 mm/sec. Doppler waveforms were analyzed for differences in the systolic peak to end-diastolic velocity ratio for these three vascular beds. Peak flow velocity and time velocity integral were also analyzed for the cerebral and renal vascular beds. The data were analyzed with the paired t test.

RESULTS

A significant decrease in the systolic-to-diastolic-velocity ratio of the middle cerebral artery occurred with 3% carbon dioxide inhalation (p < 0.02). The other vascular beds had no demonstrable change.

CONCLUSION

Transient maternal breathing of 3% carbon dioxide gas mixture selectively causes a decrease in resistance in the fetal cerebral circulation.

Indirect relation between rises in oxygen consumption and left ventricular output at birth in lambs

To examine the relation between increased newborn oxygen requirements and the postnatal rise in cardiac output, we measured left ventricular (LV) output, organ blood flows, and whole-body oxygen consumption using radioactive microspheres in late-gestation sheep fetuses and in the same animals 1 and 4 hours after cesarean section delivery. LV output rose from 264 +/- 23 ml.min-1.kg body wt-1 in fetuses to 444 +/- 33 ml.min-1.kg body wt-1 in lambs at 1 hour after delivery (p less than 0.005) and was unchanged at 4 hours after delivery. This rise in LV output was associated with a more than fourfold increase in the LV flow contribution to tissues situated distal to the ductus arteriosus (fetus, 51 +/- 9 ml.min-1.kg body wt-1; lamb, 226 +/- 22 ml.min-1.kg body wt-1; p less than 0.005), which were mainly perfused by the right ventricle in utero. However, average blood flow to body tissues was similar in fetuses (37 +/- 4 ml.min-1.100 g tissue-1), 1-hour lambs (39 +/- 4 ml.min-1.100 g tissue-1), and 4-hour lambs (40 +/- 5 ml.min-1.100 g tissue-1). Oxygen consumption increased by 58%, from 7.84 +/- 0.43 ml.min-1.kg body wt-1 in fetuses to 12.38 +/- 2.4 ml.min-1.kg body wt-1 in 1-hour lambs (p less than 0.01), and was unchanged in 4-hour lambs.(ABSTRACT TRUNCATED AT 250 WORDS)

Femoral artery blood flow monitoring has distinct advantages for examining redistribution of blood flow in fetal acidosis

Changes of blood flow in umbilical artery, carotid artery and femoral artery were examined during the progression of acidemia in fetal sheep by means of indwelling transit-time ultrasonic blood flow meters. Moreover, catecholamines in fetal blood were measured and its interrelation to the alteration in blood flow was examined. Gradually progressing fetal acidemia was induced by repeated cord compression. Umbilical blood flow showed a initial increase thereafter maintaining a plateau through the experiment, which seemed to be dependent on fetal arterial pressure. Carotid artery flow gradually increased until the arterial pH in fetal blood declined to 7.20 and remained at this level even though the acidemia further progressed. Femoral artery flow markedly decreased around fetal arterial blood pH 7.20 and its change correlated well with the plasma level of catecholamines. This change of femoral artery flow may be evaluated by examination of the flow index as well as flow volume. Redistribution of blood flow in the progression of fetal acidemia may be initiated at around fetal arterial pH 7.20 and can be detected by studying femoral artery flow.