The effects of anaesthesia on cell death in a porcine model of neonatal hypoxic-ischaemic brain injury

Background

Hypothermia is neuroprotective after neonatal hypoxic-ischaemic brain injury. However, systemic cooling to hypothermic temperatures is a stressor and may reduce neuroprotection in awake pigs. We compared two experiments of global hypoxic-ischaemic injury in newborn pigs, in which one group received propofol-remifentanil and the other remained awake during post-insult hypothermia treatment.

Methods

In both studies, newborn pigs were anaesthetised using halothane during a 45-min global hypoxic-ischaemic insult induced by reducing Fio2 and graded hypotension until a low-voltage <7 μV electroencephalogram was achieved. On reoxygenation, the pigs were randomly allocated to receive 24 h of normothermia or hypothermia. In the first study (n=18) anaesthesia was discontinued and the pigs' tracheas were extubated. In the second study (n=14) anaesthesia was continued using propofol and remifentanil. Brain injury was assessed after 72 h by classical global histopathology, Purkinje cell count, and apoptotic cell counts in the hippocampus and cerebellum.

Results

Global injury was nearly 10-fold greater in the awake group compared with the anaesthetised group (P=0.021). Hypothermia was neuroprotective in the anaesthetised pigs but not the awake pigs. In the hippocampus, the density of cleaved caspase-3-positive cells was increased in awake compared with anaesthetised pigs in normothermia. In the cerebellum, Purkinje cell density was reduced in the awake pigs irrespective of treatment, and the number of cleaved caspase-3-positive Purkinje cells was greatly increased in hypothermic awake pigs. We detected no difference in cleaved caspase-3 in the granular cell layer or microglial reactivity across the groups.

Conclusions

Our study provides novel insights into the significance of anaesthesia/sedation during hypothermia for achieving optimal neuroprotection.

Divergent epigenetic responses to perinatal asphyxia in severe mental disorders

Epigenetic modifications influenced by environmental exposures are molecular sources of phenotypic heterogeneity found in schizophrenia and bipolar disorder and may contribute to shared etiopathogenetic mechanisms of these two disorders. Newborns who experienced perinatal asphyxia have suffered reduced oxygen delivery to the brain around the time of birth, which increases the risk of later psychiatric diagnosis. This study aimed to investigate DNA methylation in blood cells for associations with a history of perinatal asphyxia, a neurologically harmful condition occurring within the biological environment of birth. We utilized prospective data from the Medical Birth Registry of Norway to identify incidents of perinatal asphyxia in 643 individuals with schizophrenia or bipolar disorder and 676 healthy controls. We performed an epigenome wide association study to distinguish differentially methylated positions associated with perinatal asphyxia. We found an interaction between methylation and exposure to perinatal asphyxia on case-control status, wherein having a history of perinatal asphyxia was associated with an increase of methylation in healthy controls and a decrease of methylation in patients on 4 regions of DNA important for brain development and function. The differentially methylated regions were observed in genes involved in oligodendrocyte survival and axonal myelination and functional recovery (LINGO3); assembly, maturation and maintenance of the brain (BLCAP;NNAT and NANOS2) and axonal transport processes and neural plasticity (SLC2A14). These findings are consistent with the notion that an opposite epigenetic response to perinatal asphyxia, in patients compared with controls, may contribute to molecular mechanisms of risk for schizophrenia and bipolar disorder.

Therapeutic Hypothermia for Hypoxic-Ischemic Brain Injury Is More Effective in Newborn Infants than in Older Patients: Review and Hypotheses

Posthypoxic therapeutic hypothermia has been tested in newborn infants, with seven randomized trials showing consistent evidence of reduction in death, cerebral palsy, and cognitive impairment at school age. In contrast, randomized trials of hypothermia after cardiac arrest in adults have not shown consistent evidence of lasting neurological protection. The apparently greater effectiveness of therapeutic hypothermia in newborns may be due to important biological and clinical differences. One such difference is that adults are heavily colonized with microbes, and many have active inflammatory processes at the time of arrest, but few newborns are heavily colonized or infected at the time of birth. Inflammation can interfere with hypothermia's neuroprotection. A second difference is that apoptosis is more commonly the pathway of neuronal death in newborns than in adults. Hypothermia inhibits apoptosis but not necrosis. Newborns have a larger endogenous supply of stem cells (which reduce apoptosis) than adults and this may favor regeneration and protection from hypothermia and regeneration. A third difference is that immature oligodendroglia are more sensitive to free radical attack then mature oligodendroglia. Hypothermia reduces free radical release. In addition, immature brain has increased N-methyl-D-aspartate receptor subunits compared with adults and hypothermia reduces excitotoxic amino acids. Adults suffering cardiac arrest often have comorbidities such as diabetes, hypertension, and atherosclerosis, which complicate recovery, but newborn infants rarely have comorbidities before asphyxia. Adult hypothermia treatment may have been too short as no trial has cooled for longer than 48 hours, some only 24 or 12 hours, but neonatal therapeutic hypothermia has routinely lasted 72 hours. We hypothesize that this combination of differences favors the effectiveness of therapeutic hypothermia in newborn infants compared with adults.

The impact of placental genomic risk for schizophrenia and birth asphyxia on brain development

The placenta plays a role in fetal brain development, and pregnancy and birth complications can be signs of placental dysfunction. Birth asphyxia is associated with smaller head size and higher risk of developing schizophrenia (SZ), but whether birth asphyxia and placental genomic risk factors associated with SZ are related and how they might impact brain development is unclear. 433 adult patients with SZ and 870 healthy controls were clinically evaluated and underwent brain magnetic resonance imaging. Pregnancy and birth information were obtained from the Medical Birth Registry of Norway. Polygenic risk scores (PRS) from the latest genome-wide association study in SZ were differentiated into placental PRS (PlacPRS) and non-placental PRS. If the interaction between PRSs and birth asphyxia on case-control status was significant, neonatal head circumference (nHC) and adult intracranial volume (ICV) were further evaluated with these variables using multiple regression. PlacPRS in individuals with a history of birth asphyxia was associated with a higher likelihood of being a patient with SZ (t = 2.10, p = 0.018). We found a significant interaction between PlacPRS and birth asphyxia on nHC in the whole sample (t = -2.43, p = 0.008), with higher placental PRS for SZ associated with lower nHC in those with birth asphyxia. This relationship was specific to males (t = -2.71, p = 0.005) and also found with their adult ICV (t = -1.97, p = 0.028). These findings suggest that placental pathophysiology and birth asphyxia may affect early and late trajectories of brain development, particularly in males with a higher vulnerability to SZ. This knowledge might lead to new strategies of treatment and prevention in SZ.

Cerebellar growth, volume and diffusivity in children cooled for neonatal encephalopathy without cerebral palsy

Children cooled for HIE and who did not develop cerebral palsy (CP) still underperform at early school age in motor and cognitive domains and have altered supra-tentorial brain volumes and white matter connectivity. We obtained T1-weighted and diffusion-weighted MRI, motor (MABC-2) and cognitive (WISC-IV) scores from children aged 6-8 years who were cooled for HIE secondary to perinatal asphyxia without CP (cases), and controls matched for age, sex, and socioeconomic status. In 35 case children, we measured cerebellar growth from infancy (age 4-15 days after birth) to childhood. In childhood, cerebellar volumes were measured in 26 cases and 23 controls. Diffusion properties (mean diffusivity, MD and fractional anisotropy, FA) were calculated in 24 cases and 19 controls, in 9 cerebellar regions. Cases with FSIQ ≤ 85 had reduced growth of cerebellar width compared to those with FSIQ > 85 (p = 0.0005). Regional cerebellar volumes were smaller in cases compared to controls (p < 0.05); these differences were not significant when normalised to total brain volume. There were no case-control differences in MD or FA. Interposed nucleus volume was more strongly associated with IQ in cases than in controls (p = 0.0196). Other associations with developmental outcome did not differ between cases and controls.

Mammillary body abnormalities and cognitive outcomes in children cooled for neonatal encephalopathy

AIM

To evaluate mammillary body abnormalities in school-age children without cerebral palsy treated with therapeutic hypothermia for neonatal hypoxic-ischaemic encephalopathy (cases) and matched controls, and associations with cognitive outcome, hippocampal volume, and diffusivity in the mammillothalamic tract (MTT) and fornix.

METHOD

Mammillary body abnormalities were scored from T1-weighted magnetic resonance imaging (MRI) in 32 cases and 35 controls (median age [interquartile range] 7 years [6 years 7 months-7 years 7 months] and 7 years 4 months [6 years 7 months-7 years 7 months] respectively). Cognition was assessed using the Wechsler Intelligence Scale for Children, Fourth Edition. Hippocampal volume (normalized by total brain volume) was measured from T1-weighted MRI. Radial diffusivity and fractional anisotropy were measured in the MTT and fornix, from diffusion-weighted MRI using deterministic tractography.

RESULTS

More cases than controls had mammillary body abnormalities (34% vs 0%; p < 0.001). Cases with abnormal mammillary bodies had lower processing speed (p = 0.016) and full-scale IQ (p = 0.028) than cases without abnormal mammillary bodies, and lower scores than controls in all cognitive domains (p < 0.05). Cases with abnormal mammillary bodies had smaller hippocampi (left p = 0.016; right p = 0.004) and increased radial diffusivity in the right MTT (p = 0.004) compared with cases without mammillary body abnormalities.

INTERPRETATION

Cooled children with mammillary body abnormalities at school-age have reduced cognitive scores, smaller hippocampi, and altered MTT microstructure compared with those without mammillary body abnormalities, and matched controls.

WHAT THIS PAPER ADDS

Cooled children are at higher risk of mammillary body abnormalities than controls. Abnormal mammillary bodies are associated with reduced cognitive scores and smaller hippocampi. Abnormal mammillary bodies are associated with altered mammillothalamic tract diffusivity.

Brain volumes and functional outcomes in children without cerebral palsy after therapeutic hypothermia for neonatal hypoxic-ischaemic encephalopathy

AIM

To investigate whether brain volumes were reduced in children aged 6 to 8 years without cerebral palsy, who underwent therapeutic hypothermia for neonatal hypoxic-ischaemic encephalopathy (patients), and matched controls, and to examine the relation between subcortical volumes and functional outcome.

METHOD

We measured regional brain volumes in 31 patients and 32 controls (median age 7 years and 7 years 2 months respectively) from T1-weighted magnetic resonance imaging (MRI). We assessed cognition using the Wechsler Intelligence Scales for Children, Fourth Edition and motor ability using the Movement Assessment Battery for Children, Second Edition (MABC-2).

RESULTS

Patients had lower volume of whole-brain grey matter, white matter, pallidi, hippocampi, and thalami than controls (false discovery rate-corrected p < 0.05). Differences in subcortical grey-matter volumes were not independent of total brain volume (TBV). In patients, hippocampal and thalamic volumes correlated with full-scale IQ (hippocampi, r = 0.477, p = 0.010; thalami, r = 0.452, p = 0.016) and MABC-2 total score (hippocampi, r = 0.526, p = 0.004; thalami, r = 0.505, p = 0.006) independent of age, sex, and TBV. No significant correlations were found in controls. In patients, cortical injury on neonatal MRI was associated with reduced volumes of hippocampi (p = 0.001), thalami (p = 0.002), grey matter (p = 0.015), and white matter (p = 0.013).

INTERPRETATION

Children who underwent therapeutic hypothermia have reduced whole-brain grey and white-matter volumes, with associations between hippocampal and thalamic volumes and functional outcomes.

Development of the corpus callosum and cognition after neonatal encephalopathy

OBJECTIVE

Neonatal imaging studies report corpus callosum abnormalities after neonatal hypoxic-ischaemic encephalopathy (HIE), but corpus callosum development and relation to cognition in childhood are unknown. Using magnetic resonance imaging (MRI), we examined the relationship between corpus callosum size, microstructure and cognitive and motor outcomes at early school-age children cooled for HIE (cases) without cerebral palsy compared to healthy, matched controls. A secondary aim was to examine the impact of HIE-related neonatal brain injury on corpus callosum size, microstructure and growth.

METHODS

Participants aged 6-8 years underwent MRI, the Movement Assessment Battery for Children Second Edition and Wechsler Intelligence Scale for Children Fourth Edition. Cross-sectional area, volume, fractional anisotropy and radial diffusivity of the corpus callosum and five subdivisions were measured. Multivariable regression was used to assess associations between total motor score, full-scale IQ (FSIQ) and imaging metrics.

RESULTS

Adjusting for age, sex and intracranial volume, cases (N = 40) compared to controls (N = 39) demonstrated reduced whole corpus callosum area (β = -26.9, 95% confidence interval [CI] = -53.17, -0.58), volume (β = -138.5, 95% CI = -267.54, -9.56), fractional anisotropy and increased radial diffusivity (P < 0.05) within segments II-V. In cases, segment V area (β = 0.18, 95% CI = 0.004, 0.35), volume (β = 0.04, 95% CI = 0.001, 0.079), whole corpus callosum fractional anisotropy (β = 13.8 95% CI = 0.6, 27.1) and radial diffusivity (β = -11.3, 95% CI = -22.22, -0.42) were associated with FSIQ. Growth of the corpus callosum was restricted in cases with a FSIQ ≤85, and volume was reduced in cases with mild neonatal multifocal injury compared to white matter injury alone.

INTERPRETATION

Following neonatal HIE, morphological and microstructural changes in the corpus callosum are associated with reduced cognitive function at early school age.

The deleterious effect of crossfostering in rat pups on hypoxic-ischemic injury tolerance and hypothermic neuroprotection

We study the effect of hypothermia (HT) following hypoxic-ischemic (HI) brain injury in postnatal day 7 (P7) rats. In 2015, new European Union animal transport regulations prompted a change in practice at the breeding facility, which henceforth crossfostered P3 litters to P8 older lactating dam prior to transportation. It is generally assumed that crossfostering does not significantly affect the experimental results. The aim of this study was to examine whether crossfostering affects our model consistency by modifying injury susceptibility and hypothermic neuroprotection. We analysed 219 pups (56 litters) from 11 experiments conducted between 2013 and 2015: 73 non-crossfostered and 146 crossfostered pups. At P7, all pups underwent unilateral common carotid artery ligation followed by 50min of hypoxia (8% O2, 36°C). Immediately after this mild insult, the pups were randomised to post-insult normothermia (NT) or HT treatment. Pups were culled at P14. Injury was assessed by area loss of the ipsilateral hemisphere and histopathology scoring of hippocampus, cortex, thalamus, and basal ganglia. Crossfostered pups had double the injury compared to non-crossfostered pups irrespective of treatment group. Hypothermic neuroprotection was statistically significant, but with a smaller and less consistent effect in crossfostered pups (relative neuroprotection 16% vs. 31% in non-crossfostered). These results demonstrate hypothermic neuroprotection following a mild HI insult. A representative subset of 41 animals were also assessed for evidence of microglial reactivity, however no detectable difference in microglial reactivity was observed between any of the groups. In conclusion, crossfostering alters outcomes in our established model through reduced insult tolerance and variable neuroprotection. Crossfostering as a common breeding practice is a largely unexplored variable in animal research that may result in invalid research conclusions if inadequately adjusted for by larger group sizes. As a result, crossfostering is likely to be inconsistent with the principles of replacement, reduction, and refinement.

Physiological responses to cuddling babies with hypoxic-ischaemic encephalopathy during therapeutic hypothermia: an observational study

OBJECTIVES

To determine whether parents cuddling infants during therapeutic hypothermia (TH) would affect cooling therapy, cardiorespiratory or neurophysiological measures. The secondary aim was to explore parent-infant bonding, maternal postnatal depression and breastfeeding.

DESIGN

Prospective observational study.

SETTING

Two tertiary neonatal intensive care units (NICU).

PARTICIPANTS

Parents and their term-born infants (n=27) receiving TH and intensive care for neonatal hypoxic-ischaemic encephalopathy.

INTERVENTIONS

Cuddling up to 2 hours during TH using a standard operating procedure developed in the study (CoolCuddle).

MAIN OUTCOME MEASURES

Mean difference in temperature, cardiorespiratory and neurophysiological variables before, during and after the cuddle. Secondary outcomes were parental bonding, maternal postnatal depression and breastfeeding.

RESULTS

During 70 CoolCuddles (115 cumulative hours), there were measurable increases in rectal temperature (0.07°C (0.03 to 0.10)) and upper margin of amplitude-integrated electroencephalogram (1.80 µV (0.83 to 2.72)) and decreases in oxygen saturations (-0.57% (-1.08 to -0.05)) compared with the precuddle period. After the cuddle, there was an increase in end-tidal CO₂ (0.25 kPa (95% CI 0.14 to 0.35)) and mean blood pressure (4.09 mm Hg (95% CI 0.96 to 7.21)) compared with the precuddle period. From discharge to 8 weeks postpartum, maternal postnatal depression declined (13 (56.5%) vs 5 (23.8%), p=0.007); breastfeeding rate differed (71% vs 50%, p=0.043), but was higher than national average at discharge (70% vs 54.6%) and mother-infant bonding (median (IQR): 3 (0-6) vs 3 (1-4)) remained stable.

CONCLUSION

In this small study, CoolCuddle was associated with clinically non-significant, but measurable, changes in temperature, cardiorespiration and neurophysiology. No infant met the criteria to stop the cuddles or had any predefined adverse events. CoolCuddle may improve breastfeeding and requires investigation in different NICU settings.

Association of Birth Asphyxia With Regional White Matter Abnormalities Among Patients With Schizophrenia and Bipolar Disorders

IMPORTANCE

White matter (WM) abnormalities are commonly reported in psychiatric disorders. Whether peripartum insufficiencies in brain oxygenation, known as birth asphyxia, are associated with WM of patients with severe mental disorders is unclear.

OBJECTIVE

To examine the association between birth asphyxia and WM in adult patients with schizophrenia and bipolar disorders (BDs) compared with healthy adults.

DESIGN, SETTING, AND PARTICIPANTS

In this case-control study, all individuals participating in the ongoing Thematically Organized Psychosis project were linked to the Medical Birth Registry of Norway (MBRN), where a subset of 271 patients (case group) and 529 healthy individuals (control group) had undergone diffusion-weighted imaging (DWI). Statistical analyses were performed from June 16, 2020, to March 9, 2021.

EXPOSURES

Birth asphyxia was defined based on measures from standardized reporting at birth in the MBRN.

MAIN OUTCOMES AND MEASURES

Associations between birth asphyxia and WM regions of interest diffusion metrics, ie, fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD), were compared between groups using analysis of covariance, adjusted for age, age squared, and sex.

RESULTS

Of the 850 adults included in the study, 271 were in the case group (140 [52%] female individuals; mean [SD] age, 28.64 [7.43] years) and 579 were in the control group (245 [42%] female individuals; mean [SD] age, 33.54 [8.31] years). Birth asphyxia measures were identified in 15% to 16% of participants, independent of group. The posterior limb of the internal capsule (PLIC) showed a significant diagnostic group × birth asphyxia interaction (F(1, 843) = 11.46; P = .001), reflecting a stronger association between birth asphyxia and FA in the case group than the control group. RD, but not AD, also displayed a significant diagnostic group × birth asphyxia interaction (F(1, 843) = 9.28; P = .002) in the PLIC, with higher values in patients with birth asphyxia and similar effect sizes as observed for FA.

CONCLUSIONS AND RELEVANCE

In this case-control study, abnormalities in the PLIC of adult patients with birth asphyxia may suggest a greater susceptibility to hypoxia in patients with severe mental illness, which could lead to myelin damage or impeded brain development. Echoing recent early-stage schizophrenia studies, abnormalities of the PLIC are relevant to psychiatric disorders, as the PLIC contains important WM brain pathways associated with language, cognitive function, and sensory function, which are impaired in schizophrenia and BDs.

Motor function and white matter connectivity in children cooled for neonatal encephalopathy

Therapeutic hypothermia reduces the incidence of severe motor disability, such as cerebral palsy, following neonatal hypoxic-ischaemic encephalopathy. However, cooled children without cerebral palsy at school-age demonstrate motor deficits and altered white matter connectivity. In this study, we used diffusion-weighted imaging to investigate the relationship between white matter connectivity and motor performance, measured using the Movement Assessment Battery for Children-2, in children aged 6-8 years treated with therapeutic hypothermia for neonatal hypoxic-ischaemic encephalopathy at birth, who did not develop cerebral palsy (cases), and matched typically developing controls. Correlations between total motor scores and diffusion properties in major white matter tracts were assessed in 33 cases and 36 controls. In cases, significant correlations (FDR-corrected P < 0.05) were found in the anterior thalamic radiation bilaterally (left: r = 0.513; right: r = 0.488), the cingulate gyrus part of the left cingulum (r = 0.588), the hippocampal part of the left cingulum (r = 0.541), and the inferior fronto-occipital fasciculus bilaterally (left: r = 0.445; right: r = 0.494). No significant correlations were found in controls. We then constructed structural connectivity networks, for 22 cases and 32 controls, in which nodes represent brain regions and edges were determined by probabilistic tractography and weighted by fractional anisotropy. Analysis of whole-brain network metrics revealed correlations (FDR-corrected P < 0.05), in cases, between total motor scores and average node strength (r = 0.571), local efficiency (r = 0.664), global efficiency (r = 0.677), clustering coefficient (r = 0.608), and characteristic path length (r = -0.652). No significant correlations were found in controls. We then investigated edge-level association with motor function using the network-based statistic. This revealed subnetworks which exhibited group differences in the association between motor outcome and edge weights, for total motor scores (P = 0.0109) as well as for balance (P = 0.0245) and manual dexterity (P = 0.0233) domain scores. All three of these subnetworks comprised numerous frontal lobe regions known to be associated with motor function, including the superior frontal gyrus and middle frontal gyrus. The subnetwork associated with total motor scores was highly left-lateralised. These findings demonstrate an association between impaired motor function and brain organisation in school-age children treated with therapeutic hypothermia for neonatal hypoxic-ischaemic encephalopathy.

Prioritized Brain Circulation During Ergometer Cycling with Apnea and Face Immersion in Ice-Cold Water: A Case Report

Background

Successful cardiopulmonary resuscitation after drowning or avalanche is often attributed to hypothermia-induced decrease in metabolism, which adapts the oxygen demand to the amount supplied under cardiac compression. Four decades ago, we speculated if oxygen-sparing mechanisms like those found in marine mammals, may improve cerebral oxygenation during acute airway blockade in humans. We investigated hemodynamic changes during steady state ergometer cycling with intermittent periods of apnea and face immersion (AFI) in ice-cold water. During AFI, heart rate (HR) dropped by 58% whereas average blood velocity (ABV) determined by means of a Doppler ultrasound velocity meter (UNIDOP University of Oslo, Oslo, Norway) fell by 85% in the radial artery and rose by 67% in the vertebral artery. Similar changes occured in radial artery ABV, albeit more slowly, when the test subject only held his breath while cycling. When he breathed via a snorkel during face immersion, HR remained unchanged while radial artery ABV fell transiently and subsequently returned to its pre-immersion level. These findings later were confirmed by other investigators. Moreover, a recent study revealed that the seal even has a system for selective brain cooling during the dive.

Conclusion

Our research has confirmed prioritized cerebral circulation during AFI in cold water. We hypothesize that these changes may improve brain oxygenation due both to greater blood flow and possibly also to faster brain cooling, as demonstrated in diving seals.

Unanswered questions regarding therapeutic hypothermia for neonates with neonatal encephalopathy

Therapeutic hypothermia (TH) is now well established to improve intact survival after neonatal encephalopathy (NE). However, many questions could not be addressed by the randomized controlled trials. Should late preterm newborns with NE be cooled? Is cooling beneficial for mild NE? Is the current therapeutic time window optimal, or could it be shortened or prolonged? Will either milder or deeper hypothermia be effective? Does infection/inflammation exposure in the perinatal period in combination with NE offer potentially beneficial preconditioning or might it obviate hypothermic neuroprotection? In the present review, we dissect the evidence, for whom, when and how can TH best be delivered, and highlight areas that need further research.

An Age-Specific Atlas for Delineation of White Matter Pathways in Children Aged 6-8 Years

Introduction

Diffusion MRI allows non-invasive assessment of white matter connectivity in typical development and of changes due to brain injury or pathology. Probabilistic white matter atlases allow diffusion metrics to be measured in specific white matter pathways, and are a critical component in spatial normalisation for group analysis. However, given the known developmental changes in white matter it may be sub-optimal to use an adult template when assessing data acquired from children.

Methods

By averaging subject-specific fibre bundles from 28 children aged from 6 to 8 years, we created an age-specific probabilistic white matter atlas for 12 major white matter tracts. Using both the newly developed and Johns Hopkins adult atlases, we compared the atlas to subject-specific fibre bundles in two independent validation cohorts, assessing accuracy in terms of volumetric overlap and measured diffusion metrics.

Results

Our age-specific atlas gave better overall performance than the adult atlas, achieving higher volumetric overlap with subject-specific fibre tracking and higher correlation of FA measurements with those measured from subject-specific fibre bundles. Specifically, estimates of FA values for cortico-spinal tract, uncinate fasciculus, forceps minor, cingulate gyrus part of the cingulum and anterior thalamic radiation were all significantly more accurate when estimated with an age-specific atlas.

Discussion

The age-specific atlas allows delineation of white matter tracts in children aged 6-8 years, without the need for tractography, more accurately than when normalising to an adult atlas. To our knowledge, this is the first publicly available probabilistic atlas of white matter tracts for this age group.

Morphine and fentanyl exposure during therapeutic hypothermia does not impair neurodevelopment

BACKGROUND

Hypothermia-treated and intubated infants with moderate or severe hypoxic-ischemic encephalopathy (HIE) usually receive morphine for sedation and analgesia (SA) during therapeutic hypothermia (TH) and endotracheal ventilation. Altered drug pharmacokinetics in this population increases the risk of drug accumulation. Opioids are neurotoxic in preterm infants. In term infants undergoing TH, the long-term effects of morphine exposure are unknown. We examined the effect of opioid administration during TH on neurodevelopmental outcome and time to extubation after sedation ended.

METHODS

In this prospectively collected population-based cohort of 282 infants with HIE treated with TH (2007-2017), the cumulative opioid dose of morphine and equipotent fentanyl (10-60 µg/kg/h) administered during the first week of life was calculated. Clinical outcomes and concomitant medications were also collected. Of 258 survivors, 229 underwent Bayley-3 neurodevelopmental assessments of cognition, language and motor function at 18-24 months. Multivariate stepwise linear regression analysis was used to examine the relation between cumulative opioid dose and Bayley-3 scores. Three severity-groups (mild-moderate-severe) were stratified by early (<6 h) amplitude-integrated electroencephalography (aEEG) patterns.

FINDINGS

The cumulative dose of opioid administered as SA during TH was median (IQR) 2121 µg/kg (1343, 2741). Time to extubation was independent of SA dose (p > 0.2). There was no significant association between cumulative SA dose and any of the Bayley-3 domains when analysing the entire cohort or any of the aEEG severity groups.

INTERPRETATION

Higher cumulative opioid doses in TH-treated infants with HIE was not associated with worse Bayley-3 scores at 18-24 months of age.

FUNDING

The Bristol cooling program was funded by the Children's Medical Research Charity SPARKS managing donations for our research from the UK and US, the UK Moulton Foundation, the Lærdal Foundation for Acute Medicine in Norway and the Norwegian Research Council (JKG).

MRI combined with early clinical variables are excellent outcome predictors for newborn infants undergoing therapeutic hypothermia after perinatal asphyxia

BACKGROUND

Binary prediction-models for outcome [death, cognition, presence and severity of cerebral palsy (CP)], using MRI and early clinical data applicable for individual outcome prediction have not been developed.

METHODS

From Dec 1st 2006 until Dec 31st 2013, we recruited 178 infants into a population-based cohort with moderate or severe hypoxic-ischaemic encephalopathy (HIE) including postnatal collapse (PNC, n = 12) and additional diagnoses (n = 12) using CoolCap/TOBY-trial entry-criteria including depressed amplitude-integrated EEG (aEEG). Early clinical/biochemical variables and MRI scans (median day 8) were obtained in 168 infants. Injury severity was scored for cortex, basal ganglia/thalami (BGT), white matter (WM) and posterior limb of the internal capsule, summating to a total injury score (TIS, range 0-11). Outcome was categorized as adverse or favourable at 18-24 months from Bayley-III domains (cut-off 85) and neurological examination including CP classification.

FINDINGS

HIE and entry-aEEG severity were stable throughout the study. Outcome was favourable in 133/178 infants and adverse in 45/178: 17 died, 28 had low Cognition/Language scores, (including 9 with severe CP and 6 mild); seven had mild CP with favourable cognitive outcome. WMxBGT product scores and TIS were strong outcome predictors, and prediction improved when clinical/biochemical variables were added in binary logistic regression. The Positive Predictive Value for adverse outcome was 88%, increasing to 95% after excluding infants with PNC and additional diagnoses. Using WMxBGT in the regression predicted 8 of the 9 children with severe CP.

INTERPRETATION

Binary logistic regression with WMxBGT or TIS and clinical variables gave excellent outcome prediction being 12% better than single variable cross-tabulation. Our MRI scoring and regression models are readily accessible and deserve investigation in other cohorts for group and individual prediction.

FUNDING

We thank the National Health Service (NHS) and our Universities and funders in UK and Norway: SPARKS, The Moulton Foundation, The Norwegian Research Council, The Lærdal Foundation for Acute Medicine and charitable donations for their support for cooling therapy.

Disrupted brain connectivity in children treated with therapeutic hypothermia for neonatal encephalopathy

•

We studied brain structure in case children cooled for neonatal encephalopathy.

•

Cases did not have cerebral palsy and were matched with controls.

•

Cases had reduced fractional anisotropy in several white matter tracts.

•

Several whole-brain structural connectivity network metrics correlated with IQ.

•

We identified subnetworks associated with case status, IQ and processing speed.

Therapeutic hypothermia following neonatal encephalopathy due to birth asphyxia reduces death and cerebral palsy. However, school-age children without cerebral palsy treated with therapeutic hypothermia for neonatal encephalopathy still have reduced performance on cognitive and motor tests, attention difficulties, slower reaction times and reduced visuo-spatial processing abilities compared to typically developing controls. We acquired diffusion-weighted imaging data from school-age children without cerebral palsy treated with therapeutic hypothermia for neonatal encephalopathy at birth, and a matched control group. Voxelwise analysis (33 cases, 36 controls) confirmed reduced fractional anisotropy in widespread areas of white matter in cases, particularly in the fornix, corpus callosum, anterior and posterior limbs of the internal capsule bilaterally and cingulum bilaterally. In structural brain networks constructed using probabilistic tractography (22 cases, 32 controls), graph-theoretic measures of strength, local and global efficiency, clustering coefficient and characteristic path length were found to correlate with IQ in cases but not controls. Network-based statistic analysis implicated brain regions involved in visuo-spatial processing and attention, aligning with previous behavioural findings. These included the precuneus, thalamus, left superior parietal gyrus and left inferior temporal gyrus. Our findings demonstrate that, despite the manifest successes of therapeutic hypothermia, brain development is impaired in these children.

Closed circuit xenon delivery for 72h in neonatal piglets following hypoxic insult using an ambient pressure automated control system: Development, technical evaluation and pulmonary effects

BACKGROUND

Therapeutic hypothermia (TH) for 72h is the standard treatment following neonatal encephalopathy (NE). However, one-third do not benefit and adjunctive therapies are urgently needed. Xenon enhances neuroprotection with TH when administered at 50% concentration within 5hours of hypoxia in experimental studies. Delayed initiation (~10 hours of age) of 30% xenon for 24 hours during TH did not improve early adverse biomarkers in a clinical trial of Xenon+TH vs TH. After hypoxia-ischemia, excitotoxic injury via N-methyl-D-aspartate receptor overactivation lasts days. Since xenon partially inhibits this receptor, we hypothesised that giving 50% xenon throughout the entire 72h TH and rewarming periods would enhance neuroprotection. Xenon costs $30/litre, so a closed-circuit breathing system is desirable with automated fresh gas delivery.

METHODS

Seven mechanically ventilated newborn pigs were randomized to receive 50% inhaled xenon for 72h during hypothermia (rectal-temperature 35°C) and subsequent rewarming following a global hypoxic-ischemic insult (XeHT, N = 4) or under normothermia for 72h (rectal-temperature 38.5°C) following sham insult (XeNT, N = 3). An automated fresh gas delivery system injected oxygen/air/xenon boluses into a closed-circuit based on measured gas concentrations.

RESULTS AND DISCUSSION

Median (IQR) xenon consumption was 0.31 L/h (0.18, 0.50) and 0.34L/h (0.32, 0.49) for hypothermic and normothermic groups respectively, 0.34L/h (0.25, 0.53) overall. 92% of 9626 xenon and 69% of 9635 oxygen measurements were within 20% variation from targets. For xenon concentration, the median absolute performance errors for the XeHT and XeNT groups were 6.14% and 3.84% respectively and 4.31% overall. For oxygen these values were 13.42%, 15.05% and 12.4% respectively. There were no adverse pulmonary pathophysiology findings. Clinical problems over the total period included three related to sensors, seven breathing system leaks, ten partial and one complete tracheal tube occlusion episodes.

CONCLUSION

The automated controller functioned as intended maintaining an inhaled xenon concentration close to the 50% target for 72-78h at a xenon cost of $11.1/h.

School-age outcomes of children without cerebral palsy cooled for neonatal hypoxic-ischaemic encephalopathy in 2008-2010

OBJECTIVE

Since therapeutic hypothermia became standard care for neonatal hypoxic-ischaemic encephalopathy (HIE), even fewer infants die or have disability at 18-month assessment than in the clinical trials. However, longer term follow-up of apparently unimpaired children is lacking. We investigated the cognitive, motor and behavioural performances of survivors without cerebral palsy (CP) cooled for HIE, in comparison with matched non-HIE control children at 6-8 years.

DESIGN

Case-control study.

PARTICIPANTS

29 case children without CP, cooled in 2008-2010 and 20 age-matched, sex-matched and social class-matched term-born controls.

MEASURES

Wechsler Intelligence Scales for Children, Fourth UK Edition, Movement Assessment Battery for Children, Second Edition (MABC-2) and Strengths and Difficulties Questionnaire.

RESULTS

Cases compared with controls had significantly lower mean (SD) full-scale IQ (91 [10.37]vs105[13.41]; mean difference (MD): -13.62, 95% CI -20.53 to -6.71) and total MABC-2 scores (7.9 [3.26]vs10.2[2.86]; MD: -2.12, 95% CI -3.93 to -0.3). Mean differences were significant between cases and controls for verbal comprehension (-8.8, 95% CI -14.25 to -3.34), perceptual reasoning (-13.9, 95% CI-20.78 to -7.09), working memory (-8.2, 95% CI-16.29 to -0.17), processing speed (-11.6, 95% CI-20.69 to -2.47), aiming and catching (-1.6, 95% CI-3.26 to -0.10) and manual dexterity (-2.8, 95% CI-4.64 to -0.85). The case group reported significantly higher median (IQR) total (12 [6.5-13.5] vs 6 [2.25-10], p=0.005) and emotional behavioural difficulties (2 [1-4.5] vs 0.5 [0-2.75], p=0.03) and more case children needed extra support in school (34%vs5%, p=0.02) than the control group.

CONCLUSIONS

School-age children without CP cooled for HIE still have reduced cognitive and motor performance and more emotional difficulties than their peers, strongly supporting the need for school-age assessments.

Motor performance and cognitive correlates in children cooled for neonatal encephalopathy without cerebral palsy at school age

AIM

To investigate whether motor performance in school-age children without cerebral palsy (CP), cooled for neonatal encephalopathy, is associated with perinatal factors and 18-month developmental scores and to explore relationships between school-age motor and cognitive performance.

METHODS

Motor and cognitive performance was assessed in 29 previously cooled children at six to eight years using the Movement Assessment Battery for Children-2 (MABC-2) and the Wechsler Intelligence Scale for Children (WISC-IV). Associations between MABC-2 scores less than/equal (≤) 15th centile and perinatal factors, social/family background, 18-month Bayley-III scores and WISC-IV scores were explored.

RESULTS

Eleven of the 29 (38%) children had MABC-2 scores ≤15th centile including 7 (24%) ≤5th centile. No significant perinatal or socio-economic risk factors were identified. Motor scores <85 at 18 months failed to identify children with MABC-2 scores ≤15th centile. MABC-2 scores ≤15th centile were associated with lower Full Scale IQ (p = 0.045), Working Memory (p = 0.03) and Perceptual Reasoning (p = 0.005) scores at six to eight years and receiving greater support in school (p = 0.01).

CONCLUSION

A third of cooled children without CP had MABC-2 scores indicating motor impairment at school age that was not identified at 18 months by Bayley-III. Most children with low MABC scores needed support at school. Sub-optimal MABC-2 scores indicate need for detailed school-age cognitive evaluation.

Therapeutic Hypothermia in Neonatal Hypoxic-Ischemic Encephalopathy

PURPOSE OF REVIEW

Therapeutic hypothermia reduces death or disability in term and near-term infants with moderate-severe hypoxic-ischemic encephalopathy. Nevertheless, many infants still survive with disability, despite hypothermia, supporting further research in to ways to further improve neurologic outcomes.

RECENT FINDINGS

Recent clinical and experimental studies have refined our understanding of the key parameters for hypothermic neuroprotection, including timing of initiation, depth, and duration of hypothermia, and subsequent rewarming rate. However, important knowledge gaps remain. There is encouraging clinical evidence from a small phase II trial that combined treatment of hypothermia with recombinant erythropoietin further reduces risk of disability but definitive studies are still needed. In conclusion, recent studies suggest that current protocols for therapeutic hypothermia are near-optimal, and that the key to better neurodevelopmental outcomes is earlier diagnosis and initiation of hypothermia after birth. Further research is essential to find and evaluate ways to further improve outcomes after hypoxic-ischemic encephalopathy, including add-on therapies for therapeutic hypothermia and preventing pyrexia during labor and delivery.

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.

Hypothermia Is Neuroprotective after Severe Hypoxic-Ischaemic Brain Injury in Neonatal Rats Pre-Exposed to PAM3CSK4

BACKGROUND

Preclinical research on the neuroprotective effect of hypothermia (HT) after perinatal asphyxia has shown variable results, depending on comorbidities and insult severity. Exposure to inflammation increases vulnerability of the neonatal brain to hypoxic-ischaemic (HI) injury, and could be one explanation for those neonates whose injury is unexpectedly severe. Gram-negative type inflammatory exposure by lipopolysaccharide administration prior to a mild HI insult results in moderate brain injury, and hypothermic neuroprotection is negated. However, the neuroprotective effect of HT is fully maintained after gram-positive type inflammatory exposure by PAM3CSK4 (PAM) pre-administration in the same HI model. Whether HT is neuroprotective in severe brain injury with gram-positive inflammatory pre-exposure has not been investigated.

METHODS

59 seven-day-old rat pups were subjected to a unilateral HI insult, with left carotid artery ligation followed by 90-min hypoxia (8% O2 at Trectal 36°C). An additional 196 pups received intraperitoneal 0.9% saline (control) or PAM1 mg/kg, 8 h before undergoing the same HI insult. After randomisation to 5 h normothermia (NT37°C) or HT32°C, pups survived 1 week before they were sacrificed by perfusion fixation. Brains were harvested for hemispheric and hippocampal area loss analyses at postnatal day 14, as well as immunostaining for neuron count in the HIP CA1 region.

RESULTS

Normothermic PAM animals (PAM-NT) had a comparable median area loss (hemispheric: 60% [95% CI 33-66]; hippocampal: 61% [95% CI 29-67]) to vehicle animals (Veh-NT) (hemispheric: 58% [95% CI 11-64]; hippocampal: 60% [95% CI 19-68]), which is defined as severe brain injury. Furthermore, mortality was low and similar in the two groups (Veh-NT 4.5% vs. PAM-NT 6.6%). HT reduced hemispheric and hippocampal injury in the Veh group by 13 and 28%, respectively (hemispheric: p = 0.048; hippocampal: p = 0.042). HT also provided neuroprotection in the PAM group, reducing hemispheric injury by 22% (p = 0.03) and hippocampal injury by 37% (p = 0.027).

CONCLUSION

In these experiments with severe brain injury, Toll-like receptor-2 triggering prior to HI injury does not have an additive injurious effect, and there is a small but significant neuroprotective effect of HT. HT appears to be neuroprotective over a continuum of injury severity in this model, and the effect size tapers off with increasing area loss. Our results indicate that gram-positive inflammatory exposure prior to HI injury does not negate the neuroprotective effect of HT in severe brain injury.

Fentanyl Induces Cerebellar Internal Granular Cell Layer Apoptosis in Healthy Newborn Pigs

Background

Opioids like fentanyl are regularly used in neonates for analgesia and sedation. So far, they have been reported to be safe and eligible to use. The cerebellum has become a focus of neurodevelopmental research within the last years, as it is known to play an important role in long-lasting motor, cognitive, and other behavioral changes. The cerebellar cortex is of major importance in the coordinative role of the cerebellum and highly vulnerable to injury and impaired growth.

Objective

This study was performed to evaluate the apoptotic effect of intravenous fentanyl infusion on the cerebellum in healthy newborn pigs.

Methods

Thirteen healthy pigs (<median 12 h old) were randomized into (1) 24 h of intravenous fentanyl at normothermia (NTFe, n = 6) or (2) non-ventilated controls at normothermia (NTCTR, n = 7). Cerebellar sections were morphologically assessed after staining with hematoxylin–eosin. In addition, paired sections were immuno-stained for cell death [Cleaved caspase-3 and terminal deoxynucleotidyl transferase-mediated deoxyuridine-triphosphate nick-end labeling (TUNEL)], and positive cells were counted in defined areas of the internal granular cell layer. In total, cells in three cerebellar gyri were counted.

Results

We found that there was an increase in cells with apoptotic morphology in the internal granular cell layer in the NTFe group. For quantification, we found a significant increase in cell death in group (1) [median (range) number of caspase-3-positive cell group (1) 8 (1–22) vs. group (2) 1 (1–6) and TUNEL-positive cells (1) 6 (1–10) vs. (2) 1 (0–4)]. In both groups, there was no difference in the number of Purkinje cells. Both groups had comparable and stable physiological parameters throughout the 24 h period.

Conclusion

Twenty-four hours of continuous intravenous fentanyl infusion increased apoptosis in the internal granular cell layer in the cerebellum of healthy newborn pigs.

Neonatal Systemic Inflammation Induces Inflammatory Reactions and Brain Apoptosis in a Pathogen-Specific Manner

BACKGROUND

After neonatal asphyxia, therapeutic hypothermia (HT) is the only proven treatment option. Although established as a neuroprotective therapy, benefit from HT has been questioned when infection is a comorbidity to hypoxic-ischaemic (HI) brain injury. Gram-negative and gram-positive species activate the immune system through different pathogen recognition receptors and subsequent immunological systems. In rodent models, gram-negative (lipopolysaccharide [LPS]) and gram-positive (PAM3CSK4 [PAM]) inflammation similarly increase neuronal vulnerability to HI. Interestingly, while LPS pre-sensitisation negates the neuroprotective effect of HT, HT is highly beneficial after PAM-sensitised HI brain injury.

OBJECTIVE

We aimed to examine whether systemic gram-positive or gram-negative inflammatory sensitisation affects juvenile rat pups per se, without an HI insult.

METHODS

Neonatal 7-day-old rats (n = 215) received intraperitoneal injections of vehicle (0.9% NaCl), LPS (0.1 mg/kg), or PAM (1 mg/kg). Core temperature and weight gain were monitored. Brain cytokine expression (IL-6, IL-1β, TNF-α, and IL-10, via PCR), apoptosis (cleaved caspase 3, via Western blots), and microglial activation (Iba1, via immunohistochemistry) were examined.

RESULTS

LPS induced an immediate drop in core temperature followed by poor weight gain, none of which were seen after PAM. Furthermore, LPS induced brain apoptosis, while PAM did not. The magnitude and temporal profile of brain cytokine expression differed between LPS- and PAM-injected animals.

CONCLUSION

These findings reveal sepsis-like conditions and neuroinflammation specific to the inflammatory stimulus (gram-positive vs. gram-negative) in the neonatal rat. They emphasise the importance of pre-clinical models being pathogen dependent, and should always be carefully tailored to their clinical scenario.

Reduced infancy and childhood epilepsy following hypothermia-treated neonatal encephalopathy

OBJECTIVE

To investigate what proportion of a regional cohort of cooled infants with neonatal encephalopathy develop epilepsy (determined by the International League Against Epilepsy [ILAE] definition and the number of antiepileptic drugs [AEDs]) up to 8 years of age.

METHODS

From 2006-2013, 151 infants with perinatal asphyxia underwent 72 h cooling. Clinical and amplitude-integrated electroencepalography (aEEG) with single-channel EEG-verified neonatal seizures were treated with AEDs. Brain magnetic resonance imaging (MRI) was assessed using a 0-11 severity score. Postneonatal seizures, epilepsy rates, and AED treatments were documented. One hundred thirty-four survivors were assessed at 18-24 months; adverse outcome was defined as death or Bayley III composite Cognition/Language or Motor scores <85 and/or severe cerebral palsy or severely reduced vision/hearing. Epilepsy rates in 103 children age 4-8 years were also documented.

RESULTS

aEEG confirmed seizures occurred precooling in 77 (57%) 151 of neonates; 48% had seizures during and/or after cooling and received AEDs. Only one infant was discharged on AEDs. At 18-24 months, one third of infants had an adverse outcome including 11% mortality. At 2 years, 8 (6%) infants had an epilepsy diagnosis (ILAE definition), of whom 3 (2%) received AEDs. Of the 103 4- to 8-year-olds, 14 (13%) had developed epilepsy, with 7 (7%) receiving AEDs. Infants/children on AEDs had higher MRI scores than those not on AEDs (median [interquartile range] 9 [8-11] vs. 2 [0-4]) and poorer outcomes. Nine (64%) of 14 children with epilepsy had cerebral palsy compared to 13 (11%) of 120 without epilepsy, and 10 (71%) of 14 children with epilepsy had adverse outcomes versus 23 (19%) of 120 survivors without epilepsy. The number of different AEDs given to control neonatal seizures, aEEG severity precooling, and MRI scores predicted childhood epilepsy.

SIGNIFICANCE

We report, in a regional cohort of infants cooled for perinatal asphyxia, 6% with epilepsy at 2 years (2% on AEDs) increasing to 13% (7% on AEDs) at early school age. These AED rates are much lower than those reported in the cooling trials, even with adjusting for our cohort's milder asphyxia. Long-term follow-up is needed to document final epilepsy rates.

Hypothermic Neuronal Rescue from Infection-Sensitised Hypoxic-Ischaemic Brain Injury Is Pathogen Dependent

Perinatal infection increases the vulnerability of the neonatal brain to hypoxic-ischaemic (HI) injury. Hypothermia treatment (HT) does not provide neuroprotection after pre-insult inflammatory sensitisation by lipopolysaccharide (LPS), a gram-negative bacterial wall constituent. However, early-onset sepsis in term babies is caused by gram-positive species in more than 90% of cases, and neuro-inflammatory responses triggered through the gram-negative route (Toll-like receptor 4, TLR-4) are different from those induced through the gram-positive route via TLR-2. Whether gram-positive septicaemia sensitises the neonatal brain to hypoxia and inhibits the neuroprotective effect of HT is unknown. Seven-day-old Wistar rats (n = 178) were subjected to intraperitoneal injections of PAM3CSK4 (1 mg/kg, a synthetic TLR-2 agonist) or vehicle (0.9% NaCl). After an 8-h delay, the left carotid artery was ligated followed by 50 min of hypoxia (8% O2) at a rectal temperature of 36°C. Pups received a 5-h treatment of normothermia (NT, 37°C) or HT (32°C) immediately after the insult. Brains were harvested after 7 days' survival for hemispheric and hippocampal area loss analyses and immunolabelling of microglia (Iba1) and hippocampal neurons (NeuN). Normothermic PAM3CSK4-injected animals showed significantly more brain injury than vehicle animals (p = 0.014). Compared to NT, HT significantly reduced injury in the PAM3CSK4-injected animals, with reduced area loss (p < 0.001), reduced microglial activation (p = 0.006), and increased neuronal rescue in the CA1 region (p < 0.001). Experimental induction of a sepsis-like condition through the gram-positive pathway sensitises the brain to HI injury. HT was highly neuroprotective after the PAM3CSK4-triggered injury, suggesting HT may be neuroprotective in the presence of a gram-positive infection. These results are in strong contrast to LPS studies where HT is not neuroprotective.

Monitoring of cerebral blood flow during hypoxia-ischemia and resuscitation in the neonatal rat using laser speckle imaging

Neonatal hypoxic-ischemic encephalopathy (HIE) is associated with alterations in cerebral blood flow (CBF) as a result of perinatal asphyxia. The extent to whichCBFchanges contribute to injury, and whether treatments that ameliorate these changes might be neuroprotective, is still unknown. Higher throughput techniques to monitorCBFchanges in rodent models ofHIEcan help elucidate the underlying pathophysiology. We developed a laser speckle imaging (LSI) technique to continuously monitorCBFin six postnatal-day 10 (P10) rats simultaneously before, during, and after unilateral hypoxia-ischemia (HI, ligation of the left carotid artery followed by hypoxia in 8% oxygen). After ligation,CBFto the ligated side fell by 30% compared to the unligated side (P < 0.0001). Hypoxia induced a bilateral 55% reduction inCBF, which was partially restored by resuscitation. Compared to resuscitation in air, resuscitation in 100% oxygen increasedCBFto the ligated side by 45% (P = 0.033). Individual variability inCBFresponse to hypoxia between animals accounted for up to 24% of the variability in hemispheric area loss to the ligated side. In both P10 and P7 models of unilateralHI, resuscitation in 100% oxygen did not affect hemispheric area loss, or hippocampalCA1 pyramidal neuron counts, after 1-week survival. ContinuousCBFmonitoring usingLSIin multiple rodents simultaneously can screen potential treatment modalities that affectCBF, and provide insight into the pathophysiology ofHI.

Xenon depresses aEEG background voltage activity whilst maintaining cardiovascular stability in sedated healthy newborn pigs

BACKGROUND

Changes in electroencephalography (EEG) voltage range are used to monitor the depth of anaesthesia, as well as predict outcome after hypoxia-ischaemia in neonates. Xenon is being investigated as a potential neuroprotectant after hypoxic-ischaemic brain injury, but the effect of Xenon on EEG parameters in children or neonates is not known. This study aimed to examine the effect of 50% inhaled Xenon on background amplitude-integrated EEG (aEEG) activity in sedated healthy newborn pigs.

METHODS

Five healthy newborn pigs, receiving intravenous fentanyl sedation, were ventilated for 24 h with 50%Xenon, 30%O2 and 20%N2 at normothermia. The upper and lower voltage-range of the aEEG was continuously monitored together with cardiovascular parameters throughout a 1 h baseline period with fentanyl sedation only, followed by 24 h of Xenon administration.

RESULTS

The median (IQR) upper and lower aEEG voltage during 1 h baseline was 48.0 μV (46.0-50.0) and 25.0 μV (23.0-26.0), respectively. The median (IQR) aEEG upper and lower voltage ranges were significantly depressed to 21.5 μV (20.0-26.5) and 12.0 μV (12.0-16.5) from 10 min after the onset of 50% Xenon administration (p=0.002). After the initial Xenon induced depression in background aEEG voltage, no further aEEG changes were seen over the following 24h of ventilation with 50% xenon under fentanyl sedation. Mean arterial blood pressure and heart rate remained stable.

CONCLUSION

Mean arterial blood pressure and heart rate were not significantly influenced by 24h Xenon ventilation. 50% Xenon rapidly depresses background aEEG voltage to a steady ~50% lower level in sedated healthy newborn pigs. Therefore, care must be taken when interpreting the background voltage in neonates also receiving Xenon.

Less severe cerebral palsy outcomes in infants treated with therapeutic hypothermia

AIM

To describe the incidence, type and severity of cerebral palsy at 24 months in a regional cohort of infants treated with whole-body therapeutic hypothermia for neonatal encephalopathy.

METHODS

Data were collected prospectively in a regional centre providing TH. Antenatal and perinatal clinical variables and severity of encephalopathy were collected. Infants were assessed at 18 months using the Bayley Scales of Infant and Toddler Development-III, and the presence and severity of CP was investigated at 24 months.

RESULTS

A total of 125 of 132 infants fulfilled entry criteria for TH trials and completed 72 h of TH. Sixteen (13%) of the 125 infants died, and eight (6%) were not available for follow-up. Eighteen infants (14%; 18% of those assessed) developed CP. Of these, 12 (67%) were classified using the Gross Motor Function Classification System, at level 1, six (33%) at level 5 and none at levels 2, 3 or 4.

CONCLUSION

Our regional clinical cohort had lower mortality and comparable rates of CP compared with historical outcomes in TH trials. In contrast to historical cohorts, only one-third of the 18 children with CP were severely affected and 12 were mildly affected, all of whom were independently ambulant by 24 months.

The effect of resuscitation in 100% oxygen on brain injury in a newborn rat model of severe hypoxic-ischaemic encephalopathy

AIM

Infants with birth asphyxia frequently require resuscitation. Current guidance is to start newborn resuscitation in 21% oxygen. However, infants with severe hypoxia-ischaemia may require prolonged resuscitation with oxygen. To date, no study has looked at the effect of resuscitation in 100% oxygen following a severe hypoxic-ischaemic insult.

METHODS

Postnatal day 7 Wistar rats underwent a severe hypoxic-ischaemic insult (modified Vannucci unilateral brain injury model) followed by immediate resuscitation in either 21% or 100% oxygen for 30 min. Seven days following the insult, negative geotaxis testing was performed in survivors, and the brains were harvested. Relative ipsilateral cortical and hippocampal area loss was assessed histologically.

RESULTS

Total area loss in the affected hemisphere and area loss within the hippocampus did not significantly differ between the two groups. The same results were seen for short-term neurological assessment. No difference was seen in weight gain between pups resuscitated in 21% and 100% oxygen.

CONCLUSION

Resuscitation in 100% oxygen does not cause a deleterious effect on brain injury following a severe hypoxic-ischaemic insult in a rat model of hypoxia-ischaemia. Further work investigating the effects of resuscitation in 100% oxygen is warranted, especially for newborn infants with severe hypoxic-ischaemic encephalopathy.

Brain imaging in cooled encephalopathic neonates does not differ between four and 11 days after birth

AIM

The optimal timing of magnetic resonance imaging (MRI) in encephalopathic infants treated with hypothermia is unknown, and this study examined whether early scans differed from later scans.

METHODS

We assessed paired MRI scans carried out on 41 cooled encephalopathic infants at a median of four and 11 days using two scoring systems: the Rutherford injury scores for the basal ganglia and thalami (BGT), white matter and the posterior limb of the internal capsule, and the Bonifacio injury scores for the BGT and watershed area.

RESULTS

Both systems produced consistent injury severity scores in 37 of 41 infants on both days, with Rutherford scores predicting poor outcome in six early scans and seven later scans (K = 0.91) and Bonifacio doing the same in seven and nine scans (K = 0.85). A white matter/watershed score of two or a BGT score of one indicated severe changes by day 11 in three infants, but lower scores did not.

CONCLUSION

Magnetic resonance imaging scans indicated that the Rutherford and Bonifacio systems produced similar scores in 37 of 41 cooled encephalopathic infants at a median of four and 11 days. Infants with an early white matter/watershed scores of two or a BGT score of one may worsen and should be rescanned.

The feasibility of using a portable xenon delivery device to permit earlier xenon ventilation with therapeutic cooling of neonates during ambulance retrieval

BACKGROUND

Therapeutic hypothermia is the standard of care after perinatal asphyxia. Preclinical studies show 50% xenon improves outcome, if started early.

METHODS

During a 32-patient study randomized between hypothermia only and hypothermia with xenon, 5 neonates were given xenon during retrieval using a closed-circuit incubator-mounted system.

RESULTS

Without xenon availability during retrieval, 50% of eligible infants exceeded the 5-hour treatment window. With the transportable system, 100% were recruited. Xenon delivery lasted 55 to 120 minutes, using 174 mL/h (117.5-193.2) (median [interquartile range]), after circuit priming (1300 mL).

CONCLUSIONS

Xenon delivery during ambulance retrieval was feasible, reduced starting delays, and used very little gas.

Hypothermia Does Not Reverse Cellular Responses Caused by Lipopolysaccharide in Neonatal Hypoxic-Ischaemic Brain Injury

INTRODUCTION

Bacterial lipopolysaccharide (LPS) injection prior to hypoxia-ischaemia significantly increases hypoxia-ischaemic brain injury in 7-day-old (P7) rats. In addition, therapeutic hypothermia (HT) is not neuroprotective in this setting. However, the mechanistic aspects of this therapeutic failure have yet to be elucidated. This study was designed to investigate the underlying cellular mechanisms in this double-hit model of infection-sensitised hypoxia-ischaemic brain injury.

MATERIAL AND METHODS

P7 rat pups were injected with either vehicle or LPS, and after a 4-hour delay were exposed to left carotid ligation followed by global hypoxia inducing a unilateral stroke-like hypoxia-ischaemic injury. Pups were randomised to the following treatments: (1) vehicle-treated pups receiving normothermia treatment (NT) (Veh-NT; n = 40), (2) LPS-treated pups receiving NT treatment (LPS-NT; n = 40), (3) vehicle-treated pups receiving HT treatment (Veh-HT; n = 38) and (4) LPS-treated pups receiving HT treatment (LPS-HT; n = 35). On postnatal day 8 or 14, Western blot analysis or immunohistochemistry was performed to examine neuronal death, apoptosis, astrogliosis and microglial activation.

RESULTS

LPS sensitisation prior to hypoxia-ischaemia significantly exacerbated apoptotic neuronal loss. NeuN, a neuronal biomarker, was significantly reduced in the LPS-NT and LPS-HT groups (p = 0.008). Caspase-3 activation was significantly increased in the LPS-sensitised groups (p < 0.001). Additionally, a significant increase in astrogliosis (glial fibrillary acidic expression, p < 0.001) was seen, as well as a trend towards increased microglial activation (Iba 1 expression, p = 0.051) in LPS-sensitised animals. Treatment with HT did not counteract these changes.

CONCLUSION

LPS-sensitised hypoxia-ischaemic brain injury in newborn rats is mediated through neuronal death, apoptosis, astrogliosis and microglial activation. In this double-hit model, treatment with HT does not ameliorate these changes.

Minimal systemic hypothermia combined with selective head cooling evaluated in a pig model of hypoxia-ischemia

BACKGROUND

Selective head cooling (SHC) with moderate hypothermia (HT) and whole-body cooling are beneficial following perinatal asphyxia. SHC with systemic normothermia (NT) or minimal HT is under-investigated, could obviate systemic complications of moderate HT, and be applicable to preterm infants. We hypothesized that minimal systemic HT with SHC following hypoxia-ischemia (HI) would be neuroprotective compared with systemic NT.

METHODS

Newborn pigs underwent global HI causing permanent brain injury before being randomized to NT (rectal temperature (Trectal) 38.5 °C) or minimal HT (Trectal 37.0 °C) with SHC (cooling cap and body wrap) for 48 h followed by 24-h NT with 72-h survival.

RESULTS

SHC did not reduce global or regional neuropathology score when correcting for insult severity or compared with a NT group matched for HI severity but increased mortality by 26%. During 48 h, the SHC mean ± SD Trectal was 37.0 ± 0.2 °C, and Tdeep brain and Tsuperficial brain were 35.0 ± 1.1 °C and 31.5 ± 1.6 °C, respectively, with stable Tbrain achieved ≥ 3 h after starting cooling.

CONCLUSION

This is the first study in newborn pigs of minimal systemic HT with SHC for 48 h and a further 24 h of NT following HI. Mortality was increased in the cooled group with no neuroprotection in survivors.

Who should we cool after perinatal asphyxia?

Three ongoing challenges have arisen after the introduction of therapeutic hypothermia (TH) as standard of care for term newborns with moderate or severe perinatal asphyxia: (i) to ensure that the correct group of infants are cooled; (ii) to optimize the delivery of TH and intensive care in relation to the severity of the encephalopathy; (iii) to systematically follow up the long-term efficacy of TH using comparable outcome data between centers and countries. This review addresses the entry criteria for TH, and discusses potential issues regarding patient selection, and management of TH: cooling mild, moderate, and very severe perinatal asphyxia, cooling longer or deeper, and/or starting with a greater delay. This includes cooling of patients outside of standard trial entry criteria, such as after postnatal collapse, premature infants, those with infection, and infants with metabolic, chromosomal or surgical diagnoses in addition to perinatal asphyxia.

Cooling neonates who do not fulfil the standard cooling criteria - short- and long-term outcomes

AIM

Therapeutic hypothermia is effective and without serious adverse effects in term infants with hypoxic-ischaemic encephalopathy. It is unknown whether other neonatal patient groups could benefit from therapeutic hypothermia. Since 2006, our centre has offered cooling to infants fulfilling the standard cooling criteria, but also to those who did not.

METHODS

Observational study with prospective data collection over a 6-year period in a regional cooling centre. Complications and outcome were compared between infants who were cooled not fulfilling the standard inclusion and exclusion criteria as set out in the CoolCap/TOBY protocol (n = 36) and infants who fulfilled the standard entry criteria (n = 129).

RESULTS

21.8% of cooled infants did not fulfil standard cooling entry criteria. This included infants cooled >6 postnatal hours, late preterm infants, and infants with postnatal collapse, major cranial haemorrhage, congenital cardiac disease and surgical conditions. Complication rates and long-term outcome did not differ significantly between the groups, apart from in infants with a major cranial haemorrhage, who had higher rates of coagulopathy and the worst outcome (80% death/disability).

CONCLUSION

Cooling can be considered for infants with neonatal encephalopathy following postnatal collapse or preterm birth, those with underlying surgical or cardiac conditions, and infants starting cooling >6 postnatal hours.