Pre-existing hypoxia is associated with greater EEG suppression and early onset of evolving seizure activity during brief repeated asphyxia in near-term fetal sheep

Whole-Blood Gene Expression Profile After Hypoxic-Ischemic Encephalopathy

Importance

Induced hypothermia, the standard treatment for hypoxic-ischemic encephalopathy (HIE) in high-income countries (HICs), is less effective in the low-income populations in South Asia, who have the highest disease burden.

Objective

To investigate the differences in blood genome expression profiles of neonates with HIE from an HIC vs neonates with HIE from South Asia.

Design, Setting, and Participants

This case-control study analyzed data from (1) a prospective observational study involving neonates with moderate or severe HIE who underwent whole-body hypothermia between January 2017 and June 2019 and age-matched term healthy controls in Italy and (2) a randomized clinical trial involving neonates with moderate or severe HIE in India, Sri Lanka, and Bangladesh recruited between August 2015 and February 2019. Data were analyzed between October 2020 and August 2023.

Exposure

Whole-blood RNA that underwent next-generation sequencing.

Main Outcome and Measures

The primary outcomes were whole-blood genome expression profile at birth associated with adverse outcome (death or disability at 18 months) after HIE in the HIC and South Asia cohorts and changes in whole-genome expression profile during the first 72 hours after birth in neonates with HIE and healthy controls from the HIC cohort. Blood samples for RNA extraction were collected before whole-body hypothermia at 4 time points (6, 24, 48, and 72 hours after birth) for the HIC cohort. Only 1 blood sample was drawn within 6 hours after birth for the South Asia cohort.

Results

The HIC cohort was composed of 35 neonates (21 females [60.0%]) with a median (IQR) birth weight of 3.3 (3.0-3.6) kg and gestational age of 40.0 (39.0-40.6) weeks. The South Asia cohort consisted of 99 neonates (57 males [57.6%]) with a median (IQR) birth weight of 2.9 (2.7-3.3) kg and gestational age of 39.0 (38.0-40.0) weeks. Healthy controls included 14 neonates (9 females [64.3%]) with a median (IQR) birth weight of 3.4 (3.2-3.7) kg and gestational age of 39.2 (38.9-40.4) weeks. A total of 1793 significant genes in the HIC cohort and 99 significant genes in the South Asia cohort were associated with adverse outcome (false discovery rate <0.05). Only 11 of these genes were in common, and all had opposite direction in fold change. The most significant pathways associated with adverse outcome were downregulation of eukaryotic translation initiation factor 2 signaling in the HIC cohort (z score = -4.56; P < .001) and aldosterone signaling in epithelial cells in the South Asia cohort (z score = null; P < .001). The genome expression profile of neonates with HIE (n = 35) at birth, 24 hours, 48 hours, and 72 hours remained significantly different from that of age-matched healthy controls in the HIC cohort (n = 14).

Conclusions and Relevance

This case-control study found that disease mechanisms underlying HIE were primarily associated with acute hypoxia in the HIC cohort and nonacute hypoxia in the South Asia cohort. This finding might explain the lack of hypothermic neuroprotection.

Duration of birth depression and neurodevelopmental outcomes after whole-body hypothermia for hypoxic ischemic encephalopathy in India, Sri Lanka and Bangladesh - an exploratory analysis of the HELIX trial

Background

Effect of duration of birth depression on neurodevelopmental outcomes in low- and middle-income countries (LMICs) is not known. We examined the association of birth depression with brain injury, neurodevelopmental outcomes, and hypothermia after hypoxic ischemic encephalopathy (HIE) in south Asia.

Methods

We compared cerebral magnetic resonance (MR) at 2 weeks, and adverse outcomes (death or moderate or severe disability) at 18 months in 408 babies with moderate or severe HIE who had long birth depression (positive pressure ventilation (PPV) >10 min or Apgar score<6 at 10 min or cord pH < 7.0) and short birth depression (PPV for 5-10 min or Apgar score<6 at 5 min, but ≥6 at 10 min).

Findings

Long depression group (n = 201) had more severe HIE (32.8% versus 6.8%), mortality (47.5% versus 26.4%), death or disability at 18 months (62.2% versus 35.4%) (all p < 0.001), MR injury (Odds ratio; 95% CI) to basal ganglia (2.4 (1.3, 4.1); p = 0.003), posterior limb of internal capsule (2.3 (1.3, 4.3); p < 0.001) and white matter (1.7 (1.1, 2.7); p = 0.021), and lower thalamic N-acetylaspartate levels (7.69 ± 1.84 versus 8.29 ± 1.60); p = 0.031) than short depression group (n = 207). Three babies had no heartbeat at 5 min, of which 1 died and 2 survived with severe disability. No significant interaction between the duration of birth depression and whole-body hypothermia was seen for any of the MR biomarker or clinical outcomes.

Interpretation

Long birth depression was associated with more brain injury and adverse outcomes than short depression. Effect of hypothermia was not modified by duration of birth depression.

Funding

National Institute for Health Research.

Fetal brain response to worsening acidosis: an experimental study in a fetal sheep model of umbilical cord occlusions

Perinatal anoxia remains an important public health problem as it can lead to hypoxic-ischaemic encephalopathy (HIE) and cause significant neonatal mortality and morbidity. The mechanisms of the fetal brain's response to hypoxia are still unclear and current methods of in utero HIE prediction are not reliable. In this study, we directly analysed the brain response to hypoxia in fetal sheep using in utero EEG. Near-term fetal sheep were subjected to progressive hypoxia induced by repeated umbilical cord occlusions (UCO) at increasing frequency. EEG changes during and between UCO were analysed visually and quantitatively, and related with gasometric and haemodynamic data. EEG signal was suppressed during occlusions and progressively slowed between occlusions with the increasing severity of the occlusions. Per-occlusion EEG suppression correlated with per-occlusion bradycardia and increased blood pressure, whereas EEG slowing and amplitude decreases correlated with arterial hypotension and respiratory acidosis. The suppression of the EEG signal during cord occlusion, in parallel with cardiovascular adaptation could correspond to a rapid cerebral adaptation mechanism that may have a neuroprotective role. The progressive alteration of the signal with the severity of the occlusions would rather reflect the cerebral hypoperfusion due to the failure of the cardiovascular adaptation mechanisms.

Prediction of Fetal Blood Pressure during Labour with Deep Learning Techniques

Our objective is to develop a model for the prediction of minimum fetal blood pressure (FBP) during fetal heart rate (FHR) decelerations. Experimental data from umbilical occlusions in near-term fetal sheep (2698 occlusions from 57 near-term lambs) were used to train a convolutional neural network. This model was then used to estimate FBP for decelerations extracted from the final 90 min of 53,445 human FHR signals collected using cardiotocography. Minimum sheep FBP was predicted with a mean absolute error of 6.7 mmHg (25th, 50th, 75th percentiles of 2.3, 5.2, 9.7 mmHg), mean absolute percentage errors of 17.3% (5.5%, 12.5%, 23.9%) and a coefficient of determination R2=0.36. While the model was unable to clearly predict severe compromise at birth in humans, there is positive evidence that such a model could predict human FBP with further development. The neural network is capable of predicting FBP for many of the sheep decelerations accurately but performed far from satisfactory at identifying FHR segments that correspond to the highest or lowest minimum FBP. These results indicate that with further work and a larger, more variable training dataset, the model could achieve higher accuracy.

Whole-Body Hypothermia, Cerebral Magnetic Resonance Biomarkers, and Outcomes in Neonates With Moderate or Severe Hypoxic-Ischemic Encephalopathy Born at Tertiary Care Centers vs Other Facilities: A Nested Study Within a Randomized Clinical Trial

Importance

The association between place of birth and hypothermic neuroprotection after hypoxic-ischemic encephalopathy (HIE) in low- and middle-income countries (LMICs) is unknown.

Objective

To ascertain the association between place of birth and the efficacy of whole-body hypothermia for protection against brain injury measured by magnetic resonance (MR) biomarkers among neonates born at a tertiary care center (inborn) or other facilities (outborn).

Design, Setting, and Participants

This nested cohort study within a randomized clinical trial involved neonates at 7 tertiary neonatal intensive care units in India, Sri Lanka, and Bangladesh between August 15, 2015, and February 15, 2019. A total of 408 neonates born at or after 36 weeks' gestation with moderate or severe HIE were randomized to receive whole-body hypothermia (reduction of rectal temperatures to between 33.0 °C and 34.0 °C; hypothermia group) for 72 hours or no whole-body hypothermia (rectal temperatures maintained between 36.0 °C and 37.0 °C; control group) within 6 hours of birth, with follow-up until September 27, 2020.

Exposure

3T MR imaging, MR spectroscopy, and diffusion tensor imaging.

Main Outcomes and Measures

Thalamic N-acetyl aspartate (NAA) mmol/kg wet weight, thalamic lactate to NAA peak area ratios, brain injury scores, and white matter fractional anisotropy at 1 to 2 weeks and death or moderate or severe disability at 18 to 22 months.

Results

Among 408 neonates, the mean (SD) gestational age was 38.7 (1.3) weeks; 267 (65.4%) were male. A total of 123 neonates were inborn and 285 were outborn. Inborn neonates were smaller (mean [SD], 2.8 [0.5] kg vs 2.9 [0.4] kg; P = .02), more likely to have instrumental or cesarean deliveries (43.1% vs 24.7%; P = .01), and more likely to be intubated at birth (78.9% vs 29.1%; P = .001) than outborn neonates, although the rate of severe HIE was not different (23.6% vs 17.9%; P = .22). Magnetic resonance data from 267 neonates (80 inborn and 187 outborn) were analyzed. In the hypothermia vs control groups, the mean (SD) thalamic NAA levels were 8.04 (1.98) vs 8.31 (1.13) among inborn neonates (odds ratio [OR], -0.28; 95% CI, -1.62 to 1.07; P = .68) and 8.03 (1.89) vs 7.99 (1.72) among outborn neonates (OR, 0.05; 95% CI, -0.62 to 0.71; P = .89); the median (IQR) thalamic lactate to NAA peak area ratios were 0.13 (0.10-0.20) vs 0.12 (0.09-0.18) among inborn neonates (OR, 1.02; 95% CI, 0.96-1.08; P = .59) and 0.14 (0.11-0.20) vs 0.14 (0.10-0.17) among outborn neonates (OR, 1.03; 95% CI, 0.98-1.09; P = .18). There was no difference in brain injury scores or white matter fractional anisotropy between the hypothermia and control groups among inborn or outborn neonates. Whole-body hypothermia was not associated with reductions in death or disability, either among 123 inborn neonates (hypothermia vs control group: 34 neonates [58.6%] vs 34 [56.7%]; risk ratio, 1.03; 95% CI, 0.76-1.41), or 285 outborn neonates (hypothermia vs control group: 64 neonates [46.7%] vs 60 [43.2%]; risk ratio, 1.08; 95% CI, 0.83-1.41).

Conclusions and Relevance

In this nested cohort study, whole-body hypothermia was not associated with reductions in brain injury after HIE among neonates in South Asia, irrespective of place of birth. These findings do not support the use of whole-body hypothermia for HIE among neonates in LMICs.

Trial Registration

ClinicalTrials.gov Identifier: NCT02387385.

Fetal heart rate responses in chronic hypoxaemia with superimposed repeated hypoxaemia consistent with early labour: a controlled study in fetal sheep

OBJECTIVE

Deceleration area (DA) and capacity (DC) of the fetal heart rate can help predict risk of intrapartum fetal compromise. However, their predictive value in higher risk pregnancies is unclear. We investigated whether they can predict the onset of hypotension during brief hypoxaemia repeated at a rate consistent with early labour in fetal sheep with pre-existing hypoxaemia.

DESIGN

Prospective, controlled study.

SETTING

Laboratory.

SAMPLE

Chronically instrumented, unanaesthetised near-term fetal sheep.

METHODS

One-minute complete umbilical cord occlusions (UCOs) were performed every 5 minutes in fetal sheep with baseline p_a O₂ <17 mmHg (hypoxaemic, n = 8) and >17 mmHg (normoxic, n = 11) for 4 hours or until arterial pressure fell <20 mmHg.

MAIN OUTCOME MEASURES

DA, DC and arterial pressure.

RESULTS

Normoxic fetuses showed effective cardiovascular adaptation without hypotension and mild acidaemia (lowest arterial pressure 40.7 ± 2.8 mmHg, pH 7.35 ± 0.03). Hypoxaemic fetuses developed hypotension (lowest arterial pressure 20.8 ± 1.9 mmHg, P < 0.001) and acidaemia (final pH 7.07 ± 0.05). In hypoxaemic fetuses, decelerations showed faster falls in FHR over the first 40 seconds of UCOs but the final deceleration depth was not different to normoxic fetuses. DC was modestly higher in hypoxaemic fetuses during the penultimate (P = 0.04) and final (P = 0.012) 20 minutes of UCOs. DA was not different between groups.

CONCLUSION

Chronically hypoxaemic fetuses had early onset of cardiovascular compromise during labour-like brief repeated UCOs. DA was unable to identify developing hypotension in this setting, while DC only showed modest differences between groups. These findings highlight that DA and DC thresholds need to be adjusted for antenatal risk factors, potentially limiting their clinical utility.

Fetal growth restriction and stillbirth: Biomarkers for identifying at risk fetuses

Fetal growth restriction (FGR) is a major cause of stillbirth, prematurity and impaired neurodevelopment. Its etiology is multifactorial, but many cases are related to impaired placental development and dysfunction, with reduced nutrient and oxygen supply. The fetus has a remarkable ability to respond to hypoxic challenges and mounts protective adaptations to match growth to reduced nutrient availability. However, with progressive placental dysfunction, chronic hypoxia may progress to a level where fetus can no longer adapt, or there may be superimposed acute hypoxic events. Improving detection and effective monitoring of progression is critical for the management of complicated pregnancies to balance the risk of worsening fetal oxygen deprivation in utero, against the consequences of iatrogenic preterm birth. Current surveillance modalities include frequent fetal Doppler ultrasound, and fetal heart rate monitoring. However, nearly half of FGR cases are not detected in utero, and conventional surveillance does not prevent a high proportion of stillbirths. We review diagnostic challenges and limitations in current screening and monitoring practices and discuss potential ways to better identify FGR, and, critically, to identify the “tipping point” when a chronically hypoxic fetus is at risk of progressive acidosis and stillbirth.

Physiological control of fetal heart rate variability during labour: Implications and controversies

The interpretation of fetal heart rate (FHR) patterns is the only available method to continuously monitor fetal wellbeing during labour. One of the most important yet contentious aspects of the FHR pattern is changes in FHR variability (FHRV). Some clinical studies suggest that loss of FHRV during labour is a sign of fetal compromise so this is reflected in practice guidelines. Surprisingly, there is little systematic evidence to support this observation. In this review we methodically dissect the potential pathways controlling FHRV during labour-like hypoxaemia. Before labour, FHRV is controlled by the combined activity of the parasympathetic and sympathetic nervous systems, in part regulated by a complex interplay between fetal sleep state and behaviour. By contrast, preclinical studies using multiple autonomic blockades have now shown that sympathetic neural control of FHRV was potently suppressed between periods of labour-like hypoxaemia, and thus, that the parasympathetic system is the sole neural regulator of FHRV once FHR decelerations are present during labour. We further discuss the pattern of changes in FHRV during progressive fetal compromise and highlight potential biochemical, behavioural and clinical factors that may regulate parasympathetic-mediated FHRV during labour. Further studies are needed to investigate the regulators of parasympathetic activity to better understand the dynamic changes in FHRV and their true utility during labour. This article is protected by copyright. All rights reserved.

Parasympathetic activity is the key regulator of heart rate variability between decelerations during brief repeated umbilical cord occlusions in fetal sheep

Fetal heart rate variability (FHRV) is a widely used index of intrapartum well being. Both arms of the autonomic system regulate FHRV under normoxic conditions in the antenatal period. However, autonomic control of FHRV during labor when the fetus is exposed to repeated, brief hypoxemia during uterine contractions is poorly understood. We have previously shown that the sympathetic nervous system (SNS) does not regulate FHRV during labor-like hypoxia. We therefore investigated the hypothesis that the parasympathetic system is the main mediator of intrapartum FHRV. Twenty-six chronically instrumented fetal sheep at 0.85 of gestation received either bilateral cervical vagotomy (n = 7), atropine sulfate (n = 7), or sham treatment (control, n = 12), followed by three 1-min complete umbilical cord occlusions (UCOs) separated by 4-min reperfusion periods. Parasympathetic blockade reduced three measures of FHRV before UCOs (all P < 0.01). Between UCOs, atropine and vagotomy were associated with marked tachycardia (both P < 0.005), suppressed measures of FHRV (all P < 0.01), and abolished FHRV on visual inspection compared with the control group. Tachycardia in the atropine and vagotomy groups resolved over the first 10 min after the final UCO, in association with evidence that the SNS contribution to FHRV progressively returned during this time. Our findings support that SNS control of FHRV is acutely suppressed for at least 4 min after a deep intrapartum deceleration and takes 5-10 min to recover. The parasympathetic system is therefore likely to be the key mediator of FHRV once frequent FHR decelerations are established during labor.

Effects of β-adrenergic stimulation on fetal heart rate, heart rate variability, and T-wave elevation during brief umbilical cord occlusions in fetal sheep

Circulating catecholamines are critical for fetal adaptation to hypoxia by regulating fetal heart rate (FHR) and promoting myocardial contractility and peripheral vasoconstriction. They have been hypothesized to contribute to changes in FHR variability (FHRV) and T-wave morphology, clinical indexes of fetal well-being during labor. β-Adrenergic blockade with propranolol does not affect FHRV during labor-like hypoxemia and only attenuated the increase in T-wave height between the episodes of hypoxemia. To further investigate the potential role of catecholamines, we investigated whether pharmacological β-adrenergic stimulation could increase FHRV and T-wave elevation during intermittent labor-like hypoxemia. Nineteen chronically instrumented fetal sheep at 0.85 of gestation received isoprenaline hydrochloride (n = 7) or saline (control, n = 12), followed by three 1-min complete umbilical cord occlusions (UCOs) separated by 4-min reperfusion periods. Before the UCOs, infusion of isoprenaline increased FHR (P < 0.001), absolute-T/QRS ratio (P < 0.001), and one measure of FHRV [root-mean-square of successive RR interval differences (RMSSD), P < 0.05]. UCOs triggered deep FHR decelerations. During UCOs, isoprenaline was associated with increased FHR (P < 0.001) and absolute-T/QRS ratio (P < 0.05), but no effect on T/QRS ratio was observed when normalized to baseline before UCOs (normalized-T/QRS ratio). Between UCOs, isoprenaline increased FHR (P < 0.001) and absolute-T/QRS ratio (P < 0.05) but did not affect normalized-T/QRS ratio or any measures of FHRV. Arterial pressure was not affected by isoprenaline at any point. Our findings indicate that circulating catecholamines regulate FHR but not FHRV during labor-like hypoxemia and promote T-wave elevation between but not during intermittent fetal hypoxemia.

The physiology of intrapartum fetal compromise at term

Uterine contractions in labor result in a 60% reduction in uteroplacental perfusion, causing transient fetal and placental hypoxia. A healthy term fetus with a normally developed placenta is able to accommodate this transient hypoxia by activation of the peripheral chemoreflex, resulting in a reduction in oxygen consumption and a centralization of oxygenated blood to critical organs, namely the heart, brain, and adrenals. Providing there is adequate time for placental and fetal reperfusion between contractions, these fetuses will be able to withstand prolonged periods of intermittent hypoxia and avoid severe hypoxic injury. However, there exists a cohort of fetuses in whom abnormal placental development in the first half of pregnancy results in failure of endovascular invasion of the spiral arteries by the cytotrophoblastic cells and inadequate placental angiogenesis. This produces a high-resistance, low-flow circulation predisposing to hypoperfusion, hypoxia, reperfusion injury, and oxidative stress within the placenta. Furthermore, this renders the placenta susceptible to fluctuations and reduction in uteroplacental perfusion in response to external compression and stimuli (as occurs in labor), further reducing fetal capillary perfusion, placing the fetus at risk of inadequate gas/nutrient exchange. This placental dysfunction predisposes the fetus to intrapartum fetal compromise. In the absence of a rare catastrophic event, intrapartum fetal compromise occurs as a gradual process when there is an inability of the fetal heart to respond to the peripheral chemoreflex to maintain cardiac output. This may arise as a consequence of placental dysfunction reducing pre-labor myocardial glycogen stores necessary for anaerobic metabolism or due to an inadequate placental perfusion between contractions to restore fetal oxygen and nutrient exchange. If the hypoxic insult is severe enough and long enough, profound multiorgan injury and even death may occur. This review provides a detailed synopsis of the events that can result in placental dysfunction, how this may predispose to intrapartum fetal hypoxia, and what protective mechanisms are in place to avoid hypoxic injury.

Neonatal encephalopathy and hypoxic-ischemic encephalopathy

Acute hypoxic-ischemic encephalopathy around the time of birth remains a major cause of death and life-long disability. The key insight that led to the modern revival of studies of neuroprotection was that, after profound asphyxia, many brain cells show initial recovery from the insult during a short "latent" phase, typically lasting approximately 6h, only to die hours to days later after a "secondary" deterioration characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Studies designed around this framework showed that mild hypothermia initiated as early as possible before the onset of secondary deterioration and continued for a sufficient duration to allow the secondary deterioration to resolve is associated with potent, long-lasting neuroprotection. There is now compelling evidence from randomized controlled trials that mild to moderate induced hypothermia significantly improves survival and neurodevelopmental outcomes in infancy and mid-childhood.

Understanding Fetal Heart Rate Patterns That May Predict Antenatal and Intrapartum Neural Injury

Electronic fetal heart rate (FHR) monitoring is widely used to assess fetal well-being throughout pregnancy and labor. Both antenatal and intrapartum FHR monitoring are associated with a high negative predictive value and a very poor positive predictive value. This in part reflects the physiological resilience of the healthy fetus and the remarkable effectiveness of fetal adaptations to even severe challenges. In this way, the majority of "abnormal" FHR patterns in fact reflect a fetus' appropriate adaptive responses to adverse in utero conditions. Understanding the physiology of these adaptations, how they are reflected in the FHR trace and in what conditions they can fail is therefore critical to appreciating both the potential uses and limitations of electronic FHR monitoring.

The fetus at the tipping point: modifying the outcome of fetal asphyxia

Brain injury around birth is associated with nearly half of all cases of cerebral palsy. Although brain injury is multifactorial, particularly after preterm birth, acute hypoxia-ischaemia is a major contributor to injury. It is now well established that the severity of injury after hypoxia-ischaemia is determined by a dynamic balance between injurious and protective processes. In addition, mothers who are at risk of premature delivery have high rates of diabetes and antepartum infection/inflammation and are almost universally given treatments such as antenatal glucocorticoids and magnesium sulphate to reduce the risk of death and complications after preterm birth. We review evidence that these common factors affect responses to fetal asphyxia, often in unexpected ways. For example, glucocorticoid exposure dramatically increases delayed cell loss after acute hypoxia-ischaemia, largely through secondary hyperglycaemia. This critical new information is important to understand the effects of clinical treatments of women whose fetuses are at risk of perinatal asphyxia.

The peripheral chemoreflex: indefatigable guardian of fetal physiological adaptation to labour

The fetus is consistently exposed to repeated periods of impaired oxygen (hypoxaemia) and nutrient supply in labour. This is balanced by the healthy fetus's remarkable anaerobic tolerance and impressive ability to mount protective adaptations to hypoxaemia. The most important mediator of fetal adaptations to brief repeated hypoxaemia is the peripheral chemoreflex, a rapid reflex response to acute falls in arterial oxygen tension. The overwhelming majority of fetuses are able to respond to repeated uterine contractions without developing hypotension or hypoxic-ischaemic injury. In contrast, fetuses who are either exposed to severe hypoxaemia, for example during uterine hyperstimulation, or enter labour with reduced anaerobic reserve (e.g. as shown by severe fetal growth restriction) are at increased risk of developing intermittent hypotension and cerebral hypoperfusion. It is remarkable to note that when fetuses develop hypotension during such repeated severe hypoxaemia, it is not mediated by impaired reflex adaptation, but by failure to maintain combined ventricular output, likely due to a combination of exhaustion of myocardial glycogen and evolving myocardial injury. The chemoreflex is suppressed by relatively long periods of severe hypoxaemia of 1.5-2 min, longer than the typical contraction. Even in this setting, the peripheral chemoreflex is consistently reactivated between contractions. These findings demonstrate that the peripheral chemoreflex is an indefatigable guardian of fetal adaptation to labour.

Identifying stereotypic evolving micro-scale seizures (SEMS) in the hypoxic-ischemic EEG of the pre-term fetal sheep with a wavelet type-II fuzzy classifier

Perinatal hypoxic-ischemic encephalopathy (HIE) around the time of birth due to lack of oxygen can lead to debilitating neurological conditions such as epilepsy and cerebral palsy. Experimental data have shown that brain injury evolves over time, but during the first 6-8 hours after HIE the brain has recovered oxidative metabolism in a latent phase, and brain injury is reversible. Treatments such as therapeutic cerebral hypothermia (brain cooling) are effective when started during the latent phase, and continued for several days. Effectiveness of hypothermia is lost if started after the latent phase. Post occlusion monitoring of particular micro-scale transients in the hypoxic-ischemic (HI) Electroencephalogram (EEG), from an asphyxiated fetal sheep model in utero, could provide precursory evidence to identify potential biomarkers of injury when brain damage is still treatable. In our studies, we have reported how it is possible to automatically detect HI EEG transients in the form of spikes and sharp waves during the latent phase of the HI EEG of the preterm fetal sheep. This paper describes how to identify stereotypic evolving micro-scale seizures (SEMS) which have a relatively abrupt onset and termination in a frequency range of 1.8-3Hz (Delta waves) superimposed on a suppressed EEG amplitude background post occlusion. This research demonstrates how a Wavelet Type-II Fuzzy Logic System (WT-Type-II-FLS) can be used to automatically identify subtle abnormal SEMS that occur during the latent phase with a preliminary average validation overall performance of 78.71%±6.63 over the 390 minutes of the latent phase, post insult, using in utero pre-term hypoxic fetal sheep models.

The myths and physiology surrounding intrapartum decelerations: the critical role of the peripheral chemoreflex

A distinctive pattern of recurrent rapid falls in fetal heart rate, called decelerations, are commonly associated with uterine contractions during labour. These brief decelerations are mediated by vagal activation. The reflex triggering this vagal response has been variably attributed to a mechanoreceptor response to fetal head compression, to baroreflex activation following increased blood pressure during umbilical cord compression, and/or a Bezold-Jarisch reflex response to reduced venous return from the placenta. Although these complex explanations are still widespread today, there is no consistent evidence that they are common during labour. Instead, the only mechanism that has been systematically investigated, proven to be reliably active during labour and, crucially, capable of producing rapid decelerations is the peripheral chemoreflex. The peripheral chemoreflex is triggered by transient periods of asphyxia that are a normal phenomenon associated with all uterine contractions. This should not cause concern as the healthy fetus has a remarkable ability to adapt to these repeated but short periods of asphyxia. This means that the healthy fetus is typically not at risk of hypotension and injury during uncomplicated labour even during repeated brief decelerations. The physiologically incorrect theories surrounding decelerations that ignore the natural occurrence of repeated asphyxia probably gained widespread support to help explain why many babies are born healthy despite repeated decelerations during labour. We propose that a unified and physiological understanding of intrapartum decelerations that accepts the true nature of labour is critical to improve interpretation of intrapartum fetal heart rate patterns.

Instrumentation of Near-term Fetal Sheep for Multivariate Chronic Non-anesthetized Recordings

The chronically instrumented pregnant sheep has been used as a model of human fetal development and responses to pathophysiologic stimuli such as endotoxins, bacteria, umbilical cord occlusions, hypoxia and various pharmacological treatments. The life-saving clinical practices of glucocorticoid treatment in fetuses at risk of premature birth and the therapeutic hypothermia have been developed in this model. This is due to the unique amenability of the non-anesthetized fetal sheep to the surgical placement and maintenance of catheters and electrodes, allowing repetitive blood sampling, substance injection, recording of bioelectrical activity, application of electric stimulation and in vivo organ imaging. Here we describe the surgical instrumentation procedure required to achieve a stable chronically instrumented non-anesthetized fetal sheep model including characterization of the post-operative recovery from blood gas, metabolic and inflammation standpoints.

Adaptive shut-down of EEG activity predicts critical acidemia in the near-term ovine fetus

In fetal sheep, the electrocorticogram (ECOG) recorded directly from the cortex during repetitive heart rate (FHR) decelerations induced by umbilical cord occlusions (UCO) predictably correlates with worsening hypoxic-acidemia. In human fetal monitoring during labor, the equivalent electroencephalogram (EEG) can be recorded noninvasively from the scalp. We tested the hypothesis that combined fetal EEG – FHR monitoring allows for early detection of worsening hypoxic-acidemia similar to that shown for ECOG-FHR monitoring. Near-term fetal sheep (n = 9) were chronically instrumented with arterial and venous catheters, ECG, ECOG, and EEG electrodes and umbilical cord occluder, followed by 4 days of recovery. Repetitive UCOs of 1 min duration and increasing strength (with regard to the degree of reduction in umbilical blood flow) were induced each 2.5 min until pH dropped to <7.00. Repetitive UCOs led to marked acidosis (arterial pH 7.35 ± 0.01 to 7.00 ± 0.03). At pH of 7.22 ± 0.03 (range 7.32–7.07), and 45 ± 9 min (range 1 h 33 min–20 min) prior to attaining pH < 7.00, both ECOG and EEG amplitudes began to decrease ∼fourfold during each FHR deceleration in a synchronized manner. Confirming our hypothesis, these findings support fetal EEG as a useful adjunct to FHR monitoring during human labor for early detection of incipient fetal acidemia.

Online detection of fetal acidemia during labour by testing synchronization of EEG and heart rate: a prospective study in fetal sheep

Severe fetal acidemia during labour can result in life-lasting neurological deficits, but the timely detection of this condition is often not possible. This is because the positive predictive value (PPV) of fetal heart rate (FHR) monitoring, the mainstay of fetal health surveillance during labour, to detect concerning fetal acidemia is around 50%. In fetal sheep model of human labour, we reported that severe fetal acidemia (pH<7.00) during repetitive umbilical cord occlusions (UCOs) is preceded ∼60 minutes by the synchronization of electroencephalogram (EEG) and FHR. However, EEG and FHR are cyclic and noisy, and although the synchronization might be visually evident, it is challenging to detect automatically, a necessary condition for bedside utility. Here we present and validate a novel non-parametric statistical method to detect fetal acidemia during labour by using EEG and FHR. The underlying algorithm handles non-stationary and noisy data by recording number of abnormal episodes in both EEG and FHR. A logistic regression is then deployed to test whether these episodes are significantly related to each other. We then apply the method in a prospective study of human labour using fetal sheep model (n = 20). Our results render a PPV of 68% for detecting impending severe fetal acidemia ∼60 min prior to pH drop to less than 7.00 with 100% negative predictive value. We conclude that this method has a great potential to improve PPV for detection of fetal acidemia when it is implemented at the bedside. We outline directions for further refinement of the algorithm that will be achieved by analyzing larger data sets acquired in prospective human pilot studies.

Adaptive brain shut-down counteracts neuroinflammation in the near-term ovine fetus

Objective: Repetitive umbilical cord occlusions (UCOs) in ovine fetus leading to severe acidemia result in adaptive shut-down of electrocortical activity [electrocorticogram (ECoG)] as well as systemic and brain inflammation. We hypothesized that the fetuses with earlier ECoG shut-down as a neuroprotective mechanism in response to repetitive UCOs will show less brain inflammation and, moreover, that chronic hypoxia will impact this relationship.

Methods: Near-term fetal sheep were chronically instrumented with ECoG leads, vascular catheters, and a cord occluder and then underwent repetitive UCOs for up to 4 h or until fetal arterial pH was <7.00. Eight animals, hypoxic prior to the UCOs (SaO₂ <55%), were allowed to recover 24 h post insult, while 14 animals, 5 of whom also were chronically hypoxic, were allowed to recover 48 h post insult, after which brains were perfusion-fixed. Time of ECoG shut-down and corresponding pH were noted, as well as time to then reach pH <7.00 (ΔT). Microglia (MG) were counted as a measure of inflammation in gray matter layers 4–6 (GM4–6) where most ECoG activity is generated. Results are reported as mean ± SEM for p < 0.05.

Results: Repetitive UCOs resulted in worsening acidosis over 3–4 h with arterial pH decreasing to 6.97 ± 0.02 all UCO groups’ animals, recovering to baseline by 24 h. ECoG shut-down occurred 52 ± 7 min before reaching pH <7.00 at pH 7.23 ± 0.02 across the animal groups. MG counts were inversely correlated to ΔT in 24 h recovery animals (R = −0.84), as expected. This was not the case in normoxic 48 h recovery animals, and, surprisingly, in hypoxic 48 h recovery animals, this relationship was reversed (R = 0.90).

Conclusion: Adaptive brain shut-down during labor-like worsening acidemia counteracts neuroinflammation in a hypoxia- and time-dependent manner.