Cerebral intracellular lactic alkalosis persisting months after neonatal encephalopathy measured by magnetic resonance spectroscopy

Brain proton magnetic resonance spectroscopy and neurodevelopment after preterm birth: a systematic review

BACKGROUND

Preterm infants are at risk of neurodevelopmental impairments. At present, proton magnetic resonance spectroscopy (¹H-MRS) is used to evaluate brain metabolites in asphyxiated term infants. The aim of this review is to assess associations between cerebral ¹H-MRS and neurodevelopment after preterm birth.

METHODS

PubMed and Embase were searched to identify studies using ¹H-MRS and preterm birth. Eligible studies for this review included ¹H-MRS of the brain, gestational age ≤32 weeks, and neurodevelopment assessed at a corrected age (CA) of at least 12 months up to the age of 18 years.

RESULTS

Twenty papers evaluated ¹H-MRS in preterm infants at an age between near-term and 18 years and neurodevelopment. ¹H-MRS was performed in both white (WM) and gray matter (GM) in 12 of 20 studies. The main regions were frontal and parietal lobe for WM and basal ganglia for GM. N-acetylaspartate/choline (NAA/Cho) measured in WM and/or GM is the most common metabolite ratio associated with motor, language, and cognitive outcome at 18-24 months CA.

CONCLUSIONS

NAA/Cho in WM assessed at term-equivalent age was associated with motor, cognitive, and language outcome, and NAA/Cho in deep GM was associated with language outcome at 18-24 months CA.

IMPACT

In preterm born infants, brain metabolism assessed using ¹H-MRS at term-equivalent age is associated with motor, cognitive, and language outcomes at 18-24 months. ¹H-MRS at term-equivalent age in preterm born infants may be used as an early indication of brain development. Specific findings relating to NAA were most predictive of outcome.

An ode to fetal, infant, and toddler neuroimaging: Chronicling early clinical to research applications with MRI, and an introduction to an academic society connecting the field

Fetal, infant, and toddler neuroimaging is commonly thought of as a development of modern times (last two decades). Yet, this field mobilized shortly after the discovery and implementation of MRI technology. Here, we provide a review of the parallel advancements in the fields of fetal, infant, and toddler neuroimaging, noting the shifts from clinical to research use, and the ongoing challenges in this fast-growing field. We chronicle the pioneering science of fetal, infant, and toddler neuroimaging, highlighting the early studies that set the stage for modern advances in imaging during this developmental period, and the large-scale multi-site efforts which ultimately led to the explosion of interest in the field today. Lastly, we consider the growing pains of the community and the need for an academic society that bridges expertise in developmental neuroscience, clinical science, as well as computational and biomedical engineering, to ensure special consideration of the vulnerable mother-offspring dyad (especially during pregnancy), data quality, and image processing tools that are created, rather than adapted, for the young brain.

Melatonin for Neonatal Encephalopathy: From Bench to Bedside

Neonatal encephalopathy is a leading cause of morbidity and mortality worldwide. Although therapeutic hypothermia (HT) is now standard practice in most neonatal intensive care units in high resource settings, some infants still develop long-term adverse neurological sequelae. In low resource settings, HT may not be safe or efficacious. Therefore, additional neuroprotective interventions are urgently needed. Melatonin's diverse neuroprotective properties include antioxidant, anti-inflammatory, and anti-apoptotic effects. Its strong safety profile and compelling preclinical data suggests that melatonin is a promising agent to improve the outcomes of infants with NE. Over the past decade, the safety and efficacy of melatonin to augment HT has been studied in the neonatal piglet model of perinatal asphyxia. From this model, we have observed that the neuroprotective effects of melatonin are time-critical and dose dependent. Therapeutic melatonin levels are likely to be 15-30 mg/L and for optimal effect, these need to be achieved within the first 2-3 h after birth. This review summarises the neuroprotective properties of melatonin, the key findings from the piglet and other animal studies to date, and the challenges we face to translate melatonin from bench to bedside.

Microglia-Mediated Neurodegeneration in Perinatal Brain Injuries

Perinatal brain injuries, including encephalopathy related to fetal growth restriction, encephalopathy of prematurity, neonatal encephalopathy of the term neonate, and neonatal stroke, are a major cause of neurodevelopmental disorders. They trigger cellular and molecular cascades that lead in many cases to permanent motor, cognitive, and/or behavioral deficits. Damage includes neuronal degeneration, selective loss of subclasses of interneurons, blocked maturation of oligodendrocyte progenitor cells leading to dysmyelination, axonopathy and very likely synaptopathy, leading to impaired connectivity. The nature and severity of changes vary according to the type and severity of insult and maturation stage of the brain. Microglial activation has been demonstrated almost ubiquitously in perinatal brain injuries and these responses are key cell orchestrators of brain pathology but also attempts at repair. These divergent roles are facilitated by a diverse suite of transcriptional profiles and through a complex dialogue with other brain cell types. Adding to the complexity of understanding microglia and how to modulate them to protect the brain is that these cells have their own developmental stages, enabling them to be key participants in brain building. Of note, not only do microglia help build the brain and respond to brain injury, but they are a key cell in the transduction of systemic inflammation into neuroinflammation. Systemic inflammatory exposure is a key risk factor for poor neurodevelopmental outcomes in preterm born infants. Based on these observations, microglia appear as a key cell target for neuroprotection in perinatal brain injuries. Numerous strategies have been developed experimentally to modulate microglia and attenuate brain injury based on these strong supporting data and we will summarize these.

Proton Magnetic Resonance Spectroscopy Lactate/N-Acetylaspartate Within 48 h Predicts Cell Death Following Varied Neuroprotective Interventions in a Piglet Model of Hypoxia-Ischemia With and Without Inflammation-Sensitization

Despite therapeutic hypothermia, survivors of neonatal encephalopathy have high rates of adverse outcome. Early surrogate outcome measures are needed to speed up the translation of neuroprotection trials. Thalamic lactate (Lac)/N-acetylaspartate (NAA) peak area ratio acquired with proton (1H) magnetic resonance spectroscopy (MRS) accurately predicts 2-year neurodevelopmental outcome. We assessed the relationship between MR biomarkers acquired at 24-48 h following injury with cell death and neuroinflammation in a piglet model following various neuroprotective interventions. Sixty-seven piglets with hypoxia-ischemia, hypoxia alone, or lipopolysaccharide (LPS) sensitization were included, and neuroprotective interventions were therapeutic hypothermia, melatonin, and magnesium. MRS and diffusion-weighted imaging (DWI) were acquired at 24 and 48 h. At 48 h, experiments were terminated, and immunohistochemistry was assessed. There was a correlation between Lac/NAA and overall cell death [terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)] [mean Lac/NAA basal ganglia and thalamus (BGT) voxel r = 0.722, white matter (WM) voxel r = 0.784, p < 0.01] and microglial activation [ionized calcium-binding adapter molecule 1 (Iba1)] (BGT r = -0.786, WM r = -0.632, p < 0.01). Correlation with marker of caspase-dependent apoptosis [cleaved caspase 3 (CC3)] was lower (BGT r = -0.636, WM r = -0.495, p < 0.01). Relation between DWI and TUNEL was less robust (mean diffusivity BGT r = -0.615, fractional anisotropy BGT r = 0.523). Overall, Lac/NAA correlated best with cell death and microglial activation. These data align with clinical studies demonstrating Lac/NAA superiority as an outcome predictor in neonatal encephalopathy (NE) and support its use in preclinical and clinical neuroprotection studies.

Brain interstitial pH changes in the subacute phase of hypoxic-ischemic encephalopathy in newborn pigs

Brain interstitial pH (pHbrain) alterations play an important role in the mechanisms of neuronal injury in neonatal hypoxic-ischemic encephalopathy (HIE) induced by perinatal asphyxia. The newborn pig is an established large animal model to study HIE, however, only limited information on pHbrain alterations is available in this species and it is restricted to experimental perinatal asphyxia (PA) and the immediate reventilation. Therefore, we sought to determine pHbrain over the first 24h of HIE development in piglets. Anaesthetized, ventilated newborn pigs (n = 16) were instrumented to control major physiological parameters. pHbrain was determined in the parietal cortex using a pH-selective microelectrode. PA was induced by ventilation with a gas mixture containing 6%O2-20%CO2 for 20 min, followed by reventilation with air for 24h, then the brains were processed for histopathology assessment. The core temperature was maintained unchanged during PA (38.4±0.1 vs 38.3±0.1°C, at baseline versus the end of PA, respectively; mean±SEM). In the arterial blood, PA resulted in severe hypoxia (PaO2: 65±4 vs 23±1*mmHg, *p<0.05) as well as acidosis (pHa: 7.53±0.03 vs 6.79±0.02*) that is consistent with the observed hypercapnia (PaCO2: 37±3 vs 160±6*mmHg) and lactacidemia (1.6±0.3 vs 10.3±0.7*mmol/L). Meanwhile, pHbrain decreased progressively from 7.21±0.03 to 5.94±0.11*. Reventilation restored pHa, blood gases and metabolites within 4 hours except for PaCO2 that remained slightly elevated. pHbrain returned to 7.0 in 29.4±5.5 min and then recovered to its baseline level without showing secondary alterations during the 24 h observation period. Neuropathological assessment also confirmed neuronal injury. In conclusion, in spite of the severe acidosis and alterations in blood gases during experimental PA, pHbrain recovered rapidly and notably, there was no post-asphyxia hypocapnia that is commonly observed in many HIE babies. Thus, the neuronal injury in our piglet model is not associated with abnormal pHbrain or low PaCO2 over the first 24 h after PA.

Neuroprotection of the preterm brain

Despite notable advances in the care and survival of preterm infants, a significant proportion of preterm neonates will have life-long cognitive, behavioral, and motor deficits, and robustly effective neuroprotective strategies are still missing. These therapies must target the pathophysiologic mechanisms observed in contemporaneous infants and rely on modern epidemiology, imaging, and experimental models and assessment techniques. Two drugs, magnesium sulfate and caffeine, are already in use in several units, and although their targets are apnea of prematurity and myometrial contractility (respectively), they do offer improved odds of positive outcomes. Nevertheless, these drugs have limited efficacy, and NICU-to-NICU administration varies greatly. As such, there is an obvious need for additional specific neurotherapeutic strategies to further enhance the outcome of this very fragile population of neonates. The chapter reviews these issues, highlights bottlenecks that need to be solved for meaningful progress in the field, and proposes future innovative avenues for intervention, including delayed interventions.

Fetal and neonatal neuroimaging

Magnetic resonance imaging (MRI) can provide detail of the soft tissues of the fetal and neonatal brain that cannot be obtained by any other imaging modality. Conventional T1 and T2 weighted sequences provide anatomic detail of the normally developing brain and can demonstrate lesions, including those associated with preterm birth, hypoxic ischemic encephalopathy, perinatal arterial stroke, infections, and congenital malformations. Specialized imaging techniques can be used to assess cerebral vasculature (magnetic resonance angiography and venography), cerebral metabolism (magnetic resonance spectroscopy), cerebral perfusion (arterial spin labeling), and function (functional MRI). A wealth of quantitative tools, most of which were originally developed for the adult brain, can be applied to study the developing brain in utero and postnatally including measures of tissue microstructure obtained from diffusion MRI, morphometric studies to measure whole brain and regional tissue volumes, and automated approaches to study cortical folding. In this chapter, we aim to describe different imaging approaches for the fetal and neonatal brain, and to discuss their use in a range of clinical applications.

Current and Emerging Therapies in the Management of Hypoxic Ischemic Encephalopathy in Neonates

Neonatal hypoxic ischemic encephalopathy (HIE) presents a significant clinical burden with its high mortality and morbidity rates globally. Therapeutic hypothermia (TH) is now standard of care for infants with moderate to severe HIE, but has not definitively changed outcomes in severe HIE. In this review, we discuss newer promising markers that may help the clinician identify severity of HIE. Therapies that are beneficial and agents that hold promise for neuroprotection are described, both for use either alone or as adjuncts to TH. These include endogenous pathway modifiers such as erythropoietin and analogues, melatonin, and remote ischemic post conditioning. Stem cells have therapeutic potential in this condition, as in many other neonatal conditions. Of the agents listed, only erythropoietin and analogues are currently being evaluated in large randomized controlled trials (RCTs). Exogenous therapies such as argon and xenon, allopurinol, monosialogangliosides, and magnesium sulfate continue to be investigated. The recognition of tertiary mechanisms of brain damage has opened up new research into therapies not only to attenuate brain damage but also to promote cell repair and regeneration in a developmentally disorganized brain long after the perinatal insult. These alternative modalities may be especially important in mild HIE and in areas of the world where there is limited access to expensive hypothermia equipment and services.

[Correlation between magnetic resonance imaging score and clinical grading in neonatal hypoxic-ischemic encephalopathy]

OBJECTIVE

To investigate the correlation between magnetic resonance imaging (MRI) score and clinical grading in neonatal hypoxic-ischemic encephalopathy (HIE).

METHODS

Clinical grading was performed for 61 neonates with HIE according to the HIE clinical grading standard. The modified MRI scoring system was used to determine the injury scores on different MRI sequences. The correlation between HIE imaging score and clinical severity was analyzed.

RESULTS

The MRI score in neonates with moderate HIE was significantly lower than that in those with severe HIE (P<0.01). Neonates aged 0-7 days had the highest correlation coefficient between diffusion weighted imaging (DWI) score and total MRI score (r>0.9), and neonates aged >7 days had the highest correlation coefficient between T1-weighted imaging score and total MRI score (r=0.963). Brain MRI showed injuries in the basal ganglia/thalamus+brainstem and even the whole brain in neonates with severe HIE, while the neonates with moderate HIE had injuries in the cerebral watershed, with little involvement of the brainstem (P<0.01).

CONCLUSIONS

There is a good correlation between the MRI scoring system and clinical grading in neonatal HIE, suggesting the system can help with the clinical diagnosis and grading of HIE.

Vitamin D improves functional outcomes in neonatal hypoxic ischemic male rats treated with N-acetylcysteine and hypothermia

Hypothermia treatment neuroprotects approximately 50% of neonates who present with moderate to severe hypoxic ischemic encephalopathy (HIE). N-acetylcysteine (NAC), a potent antioxidant, is neuroprotective in combination with hypothermia in neonatal hypoxia-ischemia (HI) female rats, but less protective in males. Vitamin D is a neurosteroid, which may provide immunomodulation and improve outcomes for both sexes. We investigated the efficacy of this combination of drugs with hypothermia after severe HI, as well as potential mechanisms of vitamin D effects in the transition to chronic inflammation. DOL 7 rats were randomized to sham, or HI and hypothermia treated with either saline (HYPO), NAC (50 mg/kg/d, HNAC), or HNAC plus 1,25-dihydroxy-vitamin D₃ (0.1 μg/kg/d, HNAC + VitD) daily for 2 weeks. A second set of animals were randomized and treated for 11 days to investigate vitamin D metabolism and inflammatory mediators. Rats treated with HNAC + VitD performed significantly better on tests of strength and use of affected limb, adaptive sensorimotor skills, motor sequence learning, and working memory than either HYPO or HNAC, particularly benefiting male rats. Significantly fewer rats in the HNAC + VitD group had severe hemispheric volume loss. HI injury decreased serum vitamin D at 11 days and induced the enzyme that deactivates vitamin D in the hippocampus, particularly in males. Persistent vitamin D dysregulation was seen in both hippocampi in males, which was not reversed by hypothermia. Vitamin D in combination with hypothermia and NAC supports functional recovery in both sexes of neonatal rats significantly better than hypothermia alone or hypothermia and NAC in this severe HI model.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

Systemic pro-inflammatory cytokine status following therapeutic hypothermia in a piglet hypoxia-ischemia model

Background

Inflammatory cytokines are implicated in the pathogenesis of perinatal hypoxia-ischemia (HI). The influence of hypothermia (HT) on cytokines after HI is unclear. Our aim was to assess in a piglet asphyxia model, under normothermic (NT) and HT conditions: (i) the evolution of serum cytokines over 48 h and (ii) cerebrospinal fluid (CSF) cytokine levels at 48 h; (iii) serum pro/anti-inflammatory cytokine profile over 48 h and (iv) relation between brain injury measured by magnetic resonance spectroscopy (MRS) and brain TUNEL positive cells with serum cytokines, serum pro/anti-inflammatory cytokines and CSF cytokines.

Methods

Newborn piglets were randomized to NT (n = 5) or HT (n = 6) lasting 2–26 h after HI. Serum samples were obtained 4–6 h before, during and at 6–12 h intervals after HI; CSF was obtained at 48 h. Concentrations of interleukin (IL)-1β, −4, −6, −8, −10 and TNF-α were measured and pro/anti-inflammatory status compared between groups. White matter and thalamic voxel lactate/N-acetyl aspartate (Lac/NAA) (a measure of both oxidative metabolism and neuronal loss) were acquired at baseline, after HI and at 24 and 36 h.

Results

Lac/NAA was reduced at 36 h with HT compared to NT (p = 0.013 basal ganglia and p = 0.033 white matter). HT showed lower serum TNF-α from baseline to 12 h (p < 0.05). Time-matched (acquired within 5 h of each other) serum cytokine and MRS showed correlations between Lac/NAA and serum IL-1β and IL-10 (all p < 0.01). The pro/anti-inflammatory ratios IL-1β/IL-10, IL-6/IL-10, IL-4/IL-10 and IL-8/IL-10 were similar in NT and HT groups until 36 h (24 h for IL-6/IL-10); after this, 36 h pro/anti-inflammatory cytokine ratios in the serum were higher in HT compared to NT (p < 0.05), indicating a pro-inflammatory cytokine surge after rewarming in the HT group. In the CSF at 48 h, IL-8 was lower in the HT group (p < 0.05). At 48 h, CSF TNF-α correlated with Lac/NAA (p = 0.02) and CSF IL-8 correlated with white matter TUNEL positive cell death (p = 0.04).

Conclusions

Following cerebral HI, there was a systemic pro-inflammatory surge after rewarming in the HT group, which is counterintuitive to the putative neuroprotective effects of HT. While serum cytokines were variable, elevations in CSF inflammatory cytokines at 48 h were associated with MRS Lac/NAA and white matter cell death.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0821-x) contains supplementary material, which is available to authorized users.

Low plasma magnesium is associated with impaired brain metabolism in neonates with hypoxic-ischaemic encephalopathy

AIM

To determine the association between lowest plasma magnesium concentration and brain metabolism, and whether magnetic resonance imaging brain injury patterns moderated the association in hypoxic-ischemic encephalopathy.

METHODS

In 131 early (day-of-life 3) and 65 late (day-of-life 10) scans of term encephalopathic infants born between 2004 and 2012, we examined the association of lowest plasma magnesium (until day-of-life 3) on basal ganglia and white matter peak metabolite ratios on magnetic resonance spectroscopy independent of covariates, stratified by the predominant patterns of injury (normal, basal nuclei/total, watershed, multifocal) using multiple linear regression.

RESULTS

Lowest plasma magnesium was associated with lower white matter N-acetyl-aspartate/choline in the multifocal pattern on early scan (regression-coefficient, β: 0.13; 95% CI: 0.04, 0.22) and in the basal nuclei/total pattern on late scan (β: 0.08; 95% CI: 0.02, 0.15), and was negatively associated with basal ganglia lactate/N-acetyl-aspartate (β: -0.16; 95% CI: -0.05, -0.28) and lactate/choline (β: -0.1; 95% CI: -0.03, -0.17) ratio in the basal nuclei/total pattern on late scan independent of hypomagnesaemia correction, cooling and postmenstrual age at scan. Lowest plasma magnesium was not associated with metabolite ratios in other brain injury patterns.

CONCLUSION

In infants with hypoxic-ischaemic encephalopathy, predominant patterns of brain injury moderated the association between lowest plasma magnesium in the first three days of life and impaired brain metabolism.

Immediate remote ischemic postconditioning after hypoxia ischemia in piglets protects cerebral white matter but not grey matter

Remote ischemic postconditioning (RIPostC) is a promising therapeutic intervention whereby brief episodes of ischemia/reperfusion of one organ (limb) mitigate damage in another organ (brain) that has experienced severe hypoxia-ischemia. Our aim was to assess whether RIPostC is protective following cerebral hypoxia-ischemia in a piglet model of neonatal encephalopathy (NE) using magnetic resonance spectroscopy (MRS) biomarkers and immunohistochemistry. After hypoxia-ischemia (HI), 16 Large White female newborn piglets were randomized to: (i) no intervention (n = 8); (ii) RIPostC - with four, 10-min cycles of bilateral lower limb ischemia/reperfusion immediately after HI (n = 8). RIPostC reduced the hypoxic-ischemic-induced increase in white matter proton MRS lactate/N acetyl aspartate (p = 0.005) and increased whole brain phosphorus-31 MRS ATP (p = 0.039) over the 48 h after HI. Cell death was reduced with RIPostC in the periventricular white matter (p = 0.03), internal capsule (p = 0.002) and corpus callosum (p = 0.021); there was reduced microglial activation in corpus callosum (p = 0.001) and more surviving oligodendrocytes in corpus callosum (p = 0.029) and periventricular white matter (p = 0.001). Changes in gene expression were detected in the white matter at 48 h, including KATP channel and endothelin A receptor. Immediate RIPostC is a potentially safe and promising brain protective therapy for babies with NE with protection in white but not grey matter.

Basic Principles and Clinical Applications of Magnetic Resonance Spectroscopy in Neuroradiology

Magnetic resonance spectroscopy is a powerful tool to assist daily clinical diagnostics. This review is intended to give an overview on basic principles of the technology, discuss some of its technical aspects, and present typical applications in daily clinical routine in neuroradiology.

Inhaled 45-50% argon augments hypothermic brain protection in a piglet model of perinatal asphyxia

Cooling to 33.5 °C in babies with neonatal encephalopathy significantly reduces death and disability, however additional therapies are needed to maximize brain protection. Following hypoxia–ischemia we assessed whether inhaled 45–50% Argon from 2–26 h augmented hypothermia neuroprotection in a neonatal piglet model, using MRS and aEEG, which predict outcome in babies with neonatal encephalopathy, and immunohistochemistry. Following cerebral hypoxia–ischemia, 20 Newborn male Large White piglets < 40 h were randomized to: (i) Cooling (33 °C) from 2–26 h (n = 10); or (ii) Cooling and inhaled 45–50% Argon (Cooling + Argon) from 2–26 h (n = 8). Whole-brain phosphorus-31 and regional proton MRS were acquired at baseline, 24 and 48 h after hypoxia–ischemia. EEG was monitored. At 48 h after hypoxia–ischemia, cell death (TUNEL) was evaluated over 7 brain regions. There were no differences in body weight, duration of hypoxia–ischemia or insult severity; throughout the study there were no differences in heart rate, arterial blood pressure, blood biochemistry and inotrope support. Two piglets in the Cooling + Argon group were excluded. Comparing Cooling + Argon with Cooling there was preservation of whole-brain MRS ATP and PCr/Pi at 48 h after hypoxia–ischemia (p < 0.001 for both) and lower ¹H MRS lactate/N acetyl aspartate in white (p = 0.03 and 0.04) but not gray matter at 24 and 48 h. EEG background recovery was faster (p < 0.01) with Cooling + Argon. An overall difference between average cell-death of Cooling versus Cooling + Argon was observed (p < 0.01); estimated cells per mm² were 23.9 points lower (95% C.I. 7.3–40.5) for the Cooling + Argon versus Cooling. Inhaled 45–50% Argon from 2–26 h augmented hypothermic protection at 48 h after hypoxia–ischemia shown by improved brain energy metabolism on MRS, faster EEG recovery and reduced cell death on TUNEL. Argon may provide a cheap and practical therapy to augment cooling for neonatal encephalopathy.

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45–50% Argon augments brain protection above hypothermia after neonatal hypoxia–ischemia.

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No physiological or biochemical change occurred with the 24 h exposure of 45–50% Argon.

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45–50% Argon led to faster recovery of aEEG, and improved cerebral metabolism on MRS.

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TUNEL + cells were ~ 24 points lower per mm² with Argon augmented cooling v cooling.

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Argon was practical to administer with a standard neonatal ventilator (unlike xenon).

New horizons for newborn brain protection: enhancing endogenous neuroprotection

Intrapartum-related events are the third leading cause of childhood mortality worldwide and result in one million neurodisabled survivors each year. Infants exposed to a perinatal insult typically present with neonatal encephalopathy (NE). The contribution of pure hypoxia-ischaemia (HI) to NE has been debated; over the last decade, the sensitising effect of inflammation in the aetiology of NE and neurodisability is recognised. Therapeutic hypothermia is standard care for NE in high-income countries; however, its benefit in encephalopathic babies with sepsis or in those born following chorioamnionitis is unclear. It is now recognised that the phases of brain injury extend into a tertiary phase, which lasts for weeks to years after the initial insult and opens up new possibilities for therapy.There has been a recent focus on understanding endogenous neuroprotection and how to boost it or to supplement its effectors therapeutically once damage to the brain has occurred as in NE. In this review, we focus on strategies that can augment the body's own endogenous neuroprotection. We discuss in particular remote ischaemic postconditioning whereby endogenous brain tolerance can be activated through hypoxia/reperfusion stimuli started immediately after the index hypoxic-ischaemic insult. Therapeutic hypothermia, melatonin, erythropoietin and cannabinoids are examples of ways we can supplement the endogenous response to HI to obtain its full neuroprotective potential. Achieving the correct balance of interventions at the correct time in relation to the nature and stage of injury will be a significant challenge in the next decade.

Bumetanide for the treatment of seizures in newborn babies with hypoxic ischaemic encephalopathy (NEMO): an open-label, dose finding, and feasibility phase 1/2 trial

BACKGROUND

Preclinical data suggest that the loop-diuretic bumetanide might be an effective treatment for neonatal seizures. We aimed to assess dose and feasibility of intravenous bumetanide as an add-on to phenobarbital for treatment of neonatal seizures.

METHODS

In this open-label, dose finding, and feasibility phase 1/2 trial, we recruited full-term infants younger than 48 h who had hypoxic ischaemic encephalopathy and electrographic seizures not responding to a loading-dose of phenobarbital from eight neonatal intensive care units across Europe. Newborn babies were allocated to receive an additional dose of phenobarbital and one of four bumetanide dose levels by use of a bivariate Bayesian sequential dose-escalation design to assess safety and efficacy. We assessed adverse events, pharmacokinetics, and seizure burden during 48 h continuous electroencephalogram (EEG) monitoring. The primary efficacy endpoint was a reduction in electrographic seizure burden of more than 80% without the need for rescue antiepileptic drugs in more than 50% of infants. The trial is registered with ClinicalTrials.gov, number NCT01434225.

FINDINGS

Between Sept 1, 2011, and Sept 28, 2013, we screened 30 infants who had electrographic seizures due to hypoxic ischaemic encephalopathy. 14 of these infants (10 boys) were included in the study (dose allocation: 0·05 mg/kg, n=4; 0·1 mg/kg, n=3; 0·2 mg/kg, n=6; 0·3 mg/kg, n=1). All babies received at least one dose of bumetanide with the second dose of phenobarbital; three were withdrawn for reasons unrelated to bumetanide, and one because of dehydration. All but one infant also received aminoglycosides. Five infants met EEG criteria for seizure reduction (one on 0·05 mg/kg, one on 0·1 mg/kg and three on 0·2 mg/kg), and only two did not need rescue antiepileptic drugs (ie, met rescue criteria; one on 0·05 mg/kg and one on 0·3 mg/kg). We recorded no short-term dose-limiting toxic effects, but three of 11 surviving infants had hearing impairment confirmed on auditory testing between 17 and 108 days of age. The most common non-serious adverse reactions were moderate dehydration in one, mild hypotension in seven, and mild to moderate electrolyte disturbances in 12 infants. The trial was stopped early because of serious adverse reactions and limited evidence for seizure reduction.

INTERPRETATION

Our findings suggest that bumetanide as an add-on to phenobarbital does not improve seizure control in newborn infants who have hypoxic ischaemic encephalopathy and might increase the risk of hearing loss, highlighting the risks associated with the off-label use of drugs in newborn infants before safety assessment in controlled trials.

FUNDING

European Community's Seventh Framework Programme.

MRI for neurodevelopmental prognostication in the high-risk term infant

MRI performed in the neonatal period has become a tool widely used by clinicians and researchers to evaluate the developing brain. MRI can provide detailed anatomical resolution, enabling identification of brain injuries due to various perinatal insults. This review will focus on the link between neonatal MRI findings and later neurodevelopmental outcomes in high-risk term infants. In particular, the role of conventional and advanced MR imaging in prognosticating outcomes in neonates with hypoxic-ischemic encephalopathy, ischemic perinatal stroke, need for extracorporeal membrane oxygenation life support, congenital heart disease, and other neonatal neurological conditions will be discussed.

Magnetic resonance imaging of bilirubin encephalopathy: current limitations and future promise

Infants with chronic bilirubin encephalopathy often demonstrate abnormal bilateral, symmetric, high-signal intensity on T2-weighted magnetic resonance imaging of the globus pallidus and subthalamic nucleus, consistent with the neuropathology of kernicterus. Early magnetic resonance imaging of at-risk infants, while frequently showing increased T1-signal in these regions, may give false-positive findings due to the presence of myelin in these structures. Advanced magnetic resonance imaging including diffusion-weighted imaging, magnetic resonance spectroscopy, and diffusion tensor imaging with tractography may shed new insights into the pathogenesis of bilirubin-induced brain injury and the neural basis of long-term disability in infants and children with chronic bilirubin encephalopathy.

Proton Magnetic Resonance Spectroscopy Assessment of Fetal Brain Metabolism in Late-Onset ‘Small for Gestational Age' versus ‘Intrauterine Growth Restriction' Fetuses

Objectives: We used magnetic resonance spectroscopy (MRS) to evaluate brain metabolic differences in small fetuses near term as compared to appropriate for gestational age (AGA) fetuses. Study Design: 71 term small fetuses (estimated fetal weight <10th centile for gestational age with normal umbilical artery Doppler sonography) were subclassified as late intrauterine growth restriction (IUGR) (n = 50) or small for gestational age (SGA) (n = 21), and compared with 65 AGA fetuses. IUGR was defined by either abnormal middle cerebral artery, abnormal uterine artery Doppler sonography or estimated fetal weight <3rd centile. All participants underwent brain magnetic resonance imaging at 37 weeks of gestation, and single-voxel magnetic resonance spectra were obtained from the frontal lobe on a 3-tesla scanner. N-acetylaspartate (NAA)/choline (Cho), NAA/creatine (Cr) and Cho/Cr ratios were calculated and compared between cases and controls. The association of the metabolic ratios with the study groups was tested. Results: After MRS processing and applying quality control criteria, 31 spectra from late-onset IUGR, 11 from SGA and 30 from AGA fetuses were selected for further analysis. Both SGA and late-onset IUGR fetuses showed significantly reduced NAA/Cho levels when compared to AGA fetuses. This decrease followed a linear trend across the three clinical groups that were considered. Conclusions: Both SGA and late-onset IUGR fetuses showed differences in MRS brain metabolic ratios. The findings suggest that despite near-normal perinatal outcomes, SGA fetuses are not constitutionally small and may represent a form of growth disorder that needs to be clarified.

Diffusion-weighted imaging and magnetic resonance proton spectroscopy following preterm birth

AIM

To study the associations between magnetic resonance proton spectroscopy (MRS) data and apparent diffusion coefficients (ADC) from the preterm brain with developmental outcome at 18 months corrected age and clinical variables.

MATERIALS AND METHODS

A prospective observational cohort study of 67 infants born before 35 weeks gestational age who received both magnetic resonance imaging of the brain between 37 and 44 weeks corrected gestational age and developmental assessment around 18 months corrected age.

RESULTS

No relationships were found between ADC values and MRS results or outcome. MRS ratios involving N-acetyl aspartate (NAA) from the posterior white matter were associated with "severe" and "moderate to severe" difficulties, and fine motor scores were significantly lower in participants with a visible lactate doublet in the posterior white matter. The presence of a patent ductus arteriosus (PDA) was the only clinical factor related to NAA ratios.

CONCLUSION

Altered NAA levels in the posterior white matter may reflect subtle white matter injury associated with neuro-developmental difficulties, which may be related to a PDA. Further work is needed to assess the longer-term neuro-developmental implications of these findings, and to study the effect of PDAs on developmental outcome in later childhood/adolescence.

Na⁺/H⁺ exchangers and intracellular pH in perinatal brain injury

Encephalopathy consequent on perinatal hypoxia–ischemia occurs in 1–3 per 1,000 term births in the UK and frequently leads to serious and tragic consequences that devastate lives and families, with huge financial burdens for society. Although the recent introduction of cooling represents a significant advance, only 40 % survive with normal neurodevelopmental function. There is thus a significant unmet need for novel, safe, and effective therapies to optimize brain protection following brain injury around birth. The Na⁺/H⁺ exchanger (NHE) is a membrane protein present in many mammalian cell types. It is involved in regulating intracellular pH and cell volume. NHE1 is the most abundant isoform in the central nervous system and plays a role in cerebral damage after hypoxia–ischemia. Excessive NHE activation during hypoxia–ischemia leads to intracellular Na⁺ overload, which subsequently promotes Ca²⁺ entry via reversal of the Na⁺/Ca²⁺ exchanger. Increased cytosolic Ca²⁺ then triggers the neurotoxic cascade. Activation of NHE also leads to rapid normalization of pH_i and an alkaline shift in pH_i. This rapid recovery of brain intracellular pH has been termed pH paradox as, rather than causing cells to recover, this rapid return to normal and overshoot to alkaline values is deleterious to cell survival. Brain pH_i changes are closely involved in the control of cell death after injury: an alkalosis enhances excitability while a mild acidosis has the opposite effect. We have observed a brain alkalosis in 78 babies with neonatal encephalopathy serially studied using phosphorus-31 magnetic resonance spectroscopy during the first year after birth (151 studies throughout the year including 56 studies of 50 infants during the first 2 weeks after birth). An alkaline brain pH_i was associated with severely impaired outcome; the degree of brain alkalosis was related to the severity of brain injury on MRI and brain lactate concentration; and a persistence of an alkaline brain pH_i was associated with cerebral atrophy on MRI. Experimental animal models of hypoxia–ischemia show that NHE inhibitors are neuroprotective. Here, we review the published data on brain pH_i in neonatal encephalopathy and the experimental studies of NHE inhibition and neuroprotection following hypoxia–ischemia.

Magnetic resonance spectroscopy as a prognostic marker in neonatal hypoxic-ischemic encephalopathy: a study protocol for an individual patient data meta-analysis

BACKGROUND

The prognostic accuracy of 1H (proton) magnetic resonance spectroscopy (MRS) in neonatal hypoxic-ischemic encephalopathy has been assessed by a criticized study-based meta-analysis. An individual patient data meta-analysis may overcome some of the drawbacks encountered in the aggregate data meta-analysis. Moreover, the prognostic marker can be assessed quantitatively and the effect of covariates can be estimated.

METHODS

Diagnostic accuracy studies relevant to the study topic were retrieved. The primary authors will be invited to share the raw de-identified study data. These individual patient data will be analyzed using logistic regression analysis. A prediction tool calculating the individualized risk of very adverse outcome will be devised.

DISCUSSION

The proposed individual patient data meta-analysis provides several advantages. Inclusion and exclusion criteria can be applied more uniformly. Furthermore, adjustment is possible for confounding factors and subgroup analyses can be conducted. Our goal is to develop a prediction model for outcome in newborns with hypoxic-ischemic encephalopathy.

Resuscitation intensity at birth is associated with changes in brain metabolic development in preterm neonates

INTRODUCTION

Intensive resuscitation at birth has been linked to intraventricular haemorrhage (IVH) in the preterm neonate. However, the impact of less intensive resuscitation on more subtle alterations in brain metabolic development is largely unknown. Our objective was to determine the relationship between the intensity of neonatal resuscitation following preterm birth on brain metabolic development.

METHODS

One hundred thirty-three very preterm-born neonates (median gestational age [GA] 27 ± 2 weeks) underwent MR spectroscopic imaging early in life (median postmenstrual age 32 weeks) and again at term-equivalent age (median 40 weeks). Severity of white matter injury, IVH and cerebellar haemorrhage on magnetic resonance imaging were scored. Ratios of N-acetylaspartate (NAA) and lactate to choline (Cho) were calculated in eight regions of interest and were assessed in relation to intensiveness of resuscitation strategy (bag and mask, continuous positive airway pressure [CPAP], intubation, cardiopulmonary resuscitation [CPR]).

RESULTS

Within the first hour of life, 14 newborns had no intervention, 3 received bag and mask, 30 had CPAP, 79 were intubated and 7 had CPR. Resuscitated infants were more likely to have IVH (p = 0.02). More intensive resuscitation was associated with decreased NAA/Cho maturation (p < 0.001, adjusting for birth GA). Metabolic development was similar in neonates requiring CPAP in comparison to those receiving no intervention. The change in lactate/Cho did not differ across resuscitation categories (p = 0.8).

CONCLUSIONS

Intensity of resuscitation at birth is related to changes in metabolic brain development from early in life to term-equivalent age. Results suggest that preventing the need for intensive neonatal resuscitation may provide an opportunity to improve brain development in preterm neonates.

Melatonin augments hypothermic neuroprotection in a perinatal asphyxia model

Despite treatment with therapeutic hypothermia, almost 50% of infants with neonatal encephalopathy still have adverse outcomes. Additional treatments are required to maximize neuroprotection. Melatonin is a naturally occurring hormone involved in physiological processes that also has neuroprotective actions against hypoxic-ischaemic brain injury in animal models. The objective of this study was to assess neuroprotective effects of combining melatonin with therapeutic hypothermia after transient hypoxia-ischaemia in a piglet model of perinatal asphyxia using clinically relevant magnetic resonance spectroscopy biomarkers supported by immunohistochemistry. After a quantified global hypoxic-ischaemic insult, 17 newborn piglets were randomized to the following: (i) therapeutic hypothermia (33.5°C from 2 to 26 h after resuscitation, n = 8) and (ii) therapeutic hypothermia plus intravenous melatonin (5 mg/kg/h over 6 h started at 10 min after resuscitation and repeated at 24 h, n = 9). Cortical white matter and deep grey matter voxel proton and whole brain (31)P magnetic resonance spectroscopy were acquired before and during hypoxia-ischaemia, at 24 and 48 h after resuscitation. There was no difference in baseline variables, insult severity or any physiological or biochemical measure, including mean arterial blood pressure and inotrope use during the 48 h after hypoxia-ischaemia. Plasma levels of melatonin were 10 000 times higher in the hypothermia plus melatonin than hypothermia alone group. Melatonin-augmented hypothermia significantly reduced the hypoxic-ischaemic-induced increase in the area under the curve for proton magnetic resonance spectroscopy lactate/N-acetyl aspartate and lactate/total creatine ratios in the deep grey matter. Melatonin-augmented hypothermia increased levels of whole brain (31)P magnetic resonance spectroscopy nucleotide triphosphate/exchangeable phosphate pool. Correlating with improved cerebral energy metabolism, TUNEL-positive nuclei were reduced in the hypothermia plus melatonin group compared with hypothermia alone in the thalamus, internal capsule, putamen and caudate, and there was reduced cleaved caspase 3 in the thalamus. Although total numbers of microglia were not decreased in grey or white matter, expression of the prototypical cytotoxic microglial activation marker CD86 was decreased in the cortex at 48 h after hypoxia-ischaemia. The safety and improved neuroprotection with a combination of melatonin with cooling support phase II clinical trials in infants with moderate and severe neonatal encephalopathy.

Acid extrusion via blood-brain barrier causes brain alkalosis and seizures after neonatal asphyxia

Birth asphyxia is often associated with a high seizure burden that is predictive of poor neurodevelopmental outcome. The mechanisms underlying birth asphyxia seizures are unknown. Using an animal model of birth asphyxia based on 6-day-old rat pups, we have recently shown that the seizure burden is linked to an increase in brain extracellular pH that consists of the recovery from the asphyxia-induced acidosis, and of a subsequent plateau level well above normal extracellular pH. In the present study, two-photon imaging of intracellular pH in neocortical neurons in vivo showed that pH changes also underwent a biphasic acid–alkaline response, resulting in an alkaline plateau level. The mean alkaline overshoot was strongly suppressed by a graded restoration of normocapnia after asphyxia. The parallel post-asphyxia increase in extra- and intracellular pH levels indicated a net loss of acid equivalents from brain tissue that was not attributable to a disruption of the blood–brain barrier, as demonstrated by a lack of increased sodium fluorescein extravasation into the brain, and by the electrophysiological characteristics of the blood–brain barrier. Indeed, electrode recordings of pH in the brain and trunk demonstrated a net efflux of acid equivalents from the brain across the blood–brain barrier, which was abolished by the Na/H exchange inhibitor, N-methyl-isobutyl amiloride. Pharmacological inhibition of Na/H exchange also suppressed the seizure activity associated with the brain-specific alkalosis. Our findings show that the post-asphyxia seizures are attributable to an enhanced Na/H exchange-dependent net extrusion of acid equivalents across the blood–brain barrier and to consequent brain alkalosis. These results suggest targeting of blood–brain barrier-mediated pH regulation as a novel approach in the prevention and therapy of neonatal seizures.

Distribution of pH changes in mouse neonatal hypoxic-ischaemic insult

We assessed the distribution in brain pH after neonatal hypoxic-ischaemic insult and its correlation with local injury. Postnatal day 7 mice were injected with neutral red and underwent left carotid occlusion and exposure to 8% oxygen. Images captured from the cut surface of snap-frozen brain were used to calculate the pH from the blue-green absorbance ratios. Carotid occlusion alone had no effect, but combined with hypoxia caused rapid, biphasic pH decline, with the first plateau at 15-30 min, and the second at 60-90 min. The ipsilateral dorsal cortex, hippocampus, striatum and thalamus were most affected. Contralateral pH initially showed only 30% of the ipsilateral decline, becoming more acidotic with increasing duration. Systemic blood analysis revealed, compared with hypoxia alone, that combined insult caused a 63% decrease in blood glucose (1.3 ± 0.2 mM), a 2-fold increase in circulating lactate (17.7 ± 2.9 mM), a reduction in CO(2) to 1.9 ± 0.1 kPa and a drop in pH (7.26 ± 0.06). Re-oxygenation resulted in the normalisation of systemic changes, as well as a global alkaline rebound in brain pH at 4-6 h. A topographic comparison of brain injury showed only a partial correlation with pH changes, with the severest injury occurring in the ipsilateral hippocampus and sparing acidic parts of the contralateral cortex.

Xenon augmented hypothermia reduces early lactate/N-acetylaspartate and cell death in perinatal asphyxia

OBJECTIVE

Additional treatments for therapeutic hypothermia are required to maximize neuroprotection for perinatal asphyxial encephalopathy. We assessed neuroprotective effects of combining inhaled xenon with therapeutic hypothermia after transient cerebral hypoxia-ischemia in a piglet model of perinatal asphyxia using magnetic resonance spectroscopy (MRS) biomarkers supported by immunohistochemistry.

METHODS

Thirty-six newborn piglets were randomized (all groups n = 9), with intervention from 2 to 26 hours, to: (1) normothermia; (2) normothermia + 24 hours 50% inhaled xenon; (3) 24 hours hypothermia (33.5°C); or (4) 24 hours hypothermia (33.5°C) + 24 hours 50% inhaled xenon. Serial MRS was acquired before, during, and up to 48 hours after hypoxia-ischemia.

RESULTS

Mean arterial blood pressure was lower in all treatment groups compared with normothermia (p < 0.01) (although >40mmHg); the combined therapy group required more fluid boluses (p < 0.05) and inotropes (p < 0.001). Compared with no intervention, both hypothermia and xenon-augmented hypothermia reduced the temporal regression slope magnitudes for phosphorus-MRS inorganic phosphate/exchangeable phosphate pool (EPP) and phosphocreatine/EPP (both p < 0.05); for lactate/N-acetylaspartate (NAA), only xenon-augmented hypothermia reduced the slope (p < 0.01). Xenon-augmented hypothermia also reduced transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)(+) nuclei and caspase 3 immunoreactive cells in parasagittal cortex and putamen and increased microglial ramification in midtemporal cortex compared with the no treatment group (p < 0.05). Compared with hypothermia, however, combination treatment did not reach statistical significance for any measure. Lactate/NAA showed a strong positive correlation with TUNEL; nucleotide triphosphate/EPP showed a strong negative correlation with microglial ramification (both p < 0.01).

INTERPRETATION

Compared with no treatment, xenon-augmented hypothermia reduced cerebral MRS abnormalities and cell death markers in some brain regions. Compared with hypothermia, xenon-augmented hypothermia did not reach statistical significance for any measure. The safety and possible improved efficacy support phase II trials.

Brain alkalosis causes birth asphyxia seizures, suggesting therapeutic strategy

OBJECTIVE

The mechanisms whereby birth asphyxia leads to generation of seizures remain unidentified. To study the possible role of brain pH changes, we used a rodent model that mimics the alterations in systemic CO(2) and O(2) levels during and after intrapartum birth asphyxia.

METHODS

Neonatal rat pups were exposed for 1 hour to hypercapnia (20% CO(2) in the inhaled gas), hypoxia (9% O(2)), or both (asphyxic conditions). CO(2) levels of 10% and 5% were used for graded restoration of normocapnia. Seizures were characterized behaviorally and utilizing intracranial electroencephalography. Brain pH and oxygen were measured with intracortical microelectrodes, and blood pH, ionized calcium, carbon dioxide, oxygen, and lactate with a clinical device. The impact of the postexposure changes in brain pH on seizure burden was assessed during 2 hours after restoration of normoxia and normocapnia. N-methyl-isobutyl-amiloride, an inhibitor of Na(+) /H(+) exchange, was given intraperitoneally.

RESULTS

Whereas hypercapnia or hypoxia alone did not result in an appreciable postexposure seizure burden, recovery from asphyxic conditions was followed by a large seizure burden that was tightly paralleled by a rise in brain pH, but no change in brain oxygenation. By graded restoration of normocapnia after asphyxia, the alkaline shift in brain pH and the seizure burden were strongly suppressed. The seizures were virtually blocked by preapplication of N-methyl-isobutyl-amiloride.

INTERPRETATION

Our data indicate that brain alkalosis after recovery from birth asphyxia plays a key role in the triggering of seizures. We question the current practice of rapid restoration of normocapnia in the immediate postasphyxic period, and suggest a novel therapeutic strategy based on graded restoration of normocapnia.

Magnetic resonance biomarkers of neuroprotective effects in infants with hypoxic ischemic encephalopathy

Evaluation of infants with hypoxic ischemic encephalopathy by magnetic resonance spectroscopy and imaging is useful to direct clinical care, and may assist the evaluation of candidate neuroprotective therapies. Cerebral metabolites measured by magnetic resonance spectroscopy, and visual analysis of magnetic resonance images during the first 30 days after birth accurately predict later neurological outcome and are valid biomarkers of the key physiological processes underlying brain injury in neonatal hypoxic ischemic encephalopathy. Visual assessment of magnetic resonance images may also be a suitable surrogate outcome in studies of neuroprotective therapies but current magnetic resonance methods are relatively inefficient for use in early phase, first in human infant studies of novel neuroprotective therapies. However, diffusion tensor imaging and analysis of fractional anisotropy with tract-based spatial statistics promises to be a highly efficient biomarker and surrogate outcome for rapid preliminary evaluation of promising therapies for neonatal hypoxic ischemic injury. Standardisation of scanning protocols and data analysis between different scanners is essential.

Patterns of neonatal hypoxic-ischaemic brain injury

Enormous progress has been made in assessing the neonatal brain, using magnetic resonance imaging (MRI). In this review, we will describe the use of MRI and proton magnetic resonance spectroscopy in detecting different patterns of brain injury in (full-term) human neonates following hypoxic–ischaemic brain injury and indicate the relevance of these findings in predicting neurodevelopmental outcome.

MRI and withdrawal of life support from newborn infants with hypoxic-ischemic encephalopathy

The majority of deaths in infants with hypoxic-ischemic encephalopathy (HIE) follow decisions to withdraw life-sustaining treatment. Clinicians use prognostic tests including MRI to help determine prognosis and decide whether to consider treatment withdrawal. A recently published meta-analysis provided valuable information on the prognostic utility of magnetic resonance (MR) biomarkers in HIE and suggested, in particular, that proton MR spectroscopy is the most accurate predictor of neurodevelopmental outcome. How should this evidence influence treatment-limitation decisions? In this article I outline serious limitations in existing prognostic studies of HIE, including small sample size, selection bias, vague and overly inclusive outcome assessment, and potential self-fulfilling prophecies. Such limitations make it difficult to answer the most important prognostic question. Reanalysis of published data reveals that severe abnormalities on conventional MRI in the first week have a sensitivity of 71% (95% confidence interval: 59%-91%) and specificity of 84% (95% confidence interval: 68%-93%) for very adverse outcome in infants with moderate encephalopathy. On current evidence, MR biomarkers alone are not sufficiently accurate to direct treatment-limitation decisions. Although there may be a role for using MRI or MR spectroscopy in combination with other prognostic markers to identify infants with very adverse outcome, it is not possible from meta-analysis to define this group clearly. There is an urgent need for improved prognostic research into HIE.

Experimental treatments for hypoxic ischaemic encephalopathy

Hypoxic ischaemic encephalopathy continues to be a significant cause of death and disability worldwide. In the last 1-2 years, therapeutic hypothermia has entered clinical practice in industrialized countries and neuroprotection of the newborn has become a reality. The benefits and safety of cooling under intensive care settings have been shown consistently in trials; therapeutic hypothermia reduces death and neurological impairment at 18 months with a number needed to treat of approximately nine. Unfortunately, around half the infants who receive therapeutic hypothermia still have abnormal outcomes. Recent experimental data suggest that the addition of another agent to cooling may enhance overall protection either additively or synergistically. This review discusses agents such as inhaled xenon, N-acetylcysteine, melatonin, erythropoietin and anticonvulsants. The role of biomarkers to speed up clinical translation is discussed, in particular, the use of the cerebral magnetic resonance spectroscopy lactate/N-acetyl aspartate peak area ratios to provide early prognostic information. Finally, potential future therapies such as regeneration/repair and postconditioning are discussed.

Patterns of neonatal hypoxic-ischaemic brain injury

Enormous progress has been made in assessing the neonatal brain, using magnetic resonance imaging (MRI). In this review, we will describe the use of MRI and proton magnetic resonance spectroscopy in detecting different patterns of brain injury in (full-term) human neonates following hypoxic-ischaemic brain injury and indicate the relevance of these findings in predicting neurodevelopmental outcome.

Cerebral magnetic resonance biomarkers in neonatal encephalopathy: a meta-analysis

OBJECTIVE

Accurate prediction of neurodevelopmental outcome in neonatal encephalopathy (NE) is important for clinical management and to evaluate neuroprotective therapies. We undertook a meta-analysis of the prognostic accuracy of cerebral magnetic resonance (MR) biomarkers in infants with neonatal encephalopathy.

METHODS

We reviewed all studies that compared an MR biomarker performed during the neonatal period with neurodevelopmental outcome at > or =1 year. We followed standard methods recommended by the Cochrane Diagnostic Accuracy Method group and used a random-effects model for meta-analysis. Summary receiver operating characteristic curves and forest plots of each MR biomarker were calculated. chi(2) tests examined heterogeneity.

RESULTS

Thirty-two studies (860 infants with NE) were included in the meta-analysis. For predicting adverse outcome, conventional MRI during the neonatal period (days 1-30) had a pooled sensitivity of 91% (95% confidence interval [CI]: 87%-94%) and specificity of 51% (95% CI: 45%-58%). Late MRI (days 8-30) had higher sensitivity but lower specificity than early MRI (days 1-7). Proton MR spectroscopy deep gray matter lactate/N-acetyl aspartate (Lac/NAA) peak-area ratio (days 1-30) had 82% overall pooled sensitivity (95% CI: 74%-89%) and 95% specificity (95% CI: 88%-99%). On common study analysis, Lac/NAA had better diagnostic accuracy than conventional MRI performed at any time during neonatal period. The discriminatory powers of the posterior limb of internal capsule sign and brain-water apparent diffusion coefficient were poor.

CONCLUSIONS

Deep gray matter Lac/NAA is the most accurate quantitative MR biomarker within the neonatal period for prediction of neurodevelopmental outcome after NE. Lac/NAA may be useful in early clinical management decisions and counseling parents and as a surrogate end point in clinical trials that evaluate novel neuroprotective therapies.

Magnetic resonance spectroscopy in pediatric neuroradiology: clinical and research applications

Magnetic resonance spectroscopy (MRS) offers a unique, noninvasive approach to assess pediatric neurological abnormalities at microscopic levels by quantifying cellular metabolites. The most widely available MRS method, proton ((1)H; hydrogen) spectroscopy, is FDA approved for general use and can be ordered by clinicians for pediatric neuroimaging studies if indicated. There are a multitude of both acquisition and post-processing methods that can be used in the implementation of MR spectroscopy. MRS in pediatric neuroimaging is challenging to interpret because of dramatic normal developmental changes that occur in metabolites, particularly in the first year of life. Still, MRS has been proven to provide additional clinically relevant information for several pediatric neurological disease processes such as brain tumors, infectious processes, white matter disorders, and neonatal injury. MRS can also be used as a powerful quantitative research tool. In this article, specific research applications using MRS will be demonstrated in relation to neonatal brain injury and pediatric brain tumor imaging.

The TOBY Study. Whole body hypothermia for the treatment of perinatal asphyxial encephalopathy: a randomised controlled trial

Background

A hypoxic-ischaemic insult occurring around the time of birth may result in an encephalopathic state characterised by the need for resuscitation at birth, neurological depression, seizures and electroencephalographic abnormalities. There is an increasing risk of death or neurodevelopmental abnormalities with more severe encephalopathy. Current management consists of maintaining physiological parameters within the normal range and treating seizures with anticonvulsants.

Studies in adult and newborn animals have shown that a reduction of body temperature of 3–4°C after cerebral insults is associated with improved histological and behavioural outcome. Pilot studies in infants with encephalopathy of head cooling combined with mild whole body hypothermia and of moderate whole body cooling to 33.5°C have been reported. No complications were noted but the group sizes were too small to evaluate benefit.

Methods/Design

TOBY is a multi-centre, prospective, randomised study of term infants after perinatal asphyxia comparing those allocated to "intensive care plus total body cooling for 72 hours" with those allocated to "intensive care without cooling".

Full-term infants will be randomised within 6 hours of birth to either a control group with the rectal temperature kept at 37 +/- 0.2°C or to whole body cooling, with rectal temperature kept at 33–34°C for 72 hours. Term infants showing signs of moderate or severe encephalopathy +/- seizures have their eligibility confirmed by cerebral function monitoring. Outcomes will be assessed at 18 months of age using neurological and neurodevelopmental testing methods.

Sample size

At least 236 infants would be needed to demonstrate a 30% reduction in the relative risk of mortality or serious disability at 18 months.

Recruitment was ahead of target by seven months and approvals were obtained allowing recruitment to continue to the end of the planned recruitment phase. 325 infants were recruited.

Primary outcome

Combined rate of mortality and severe neurodevelopmental impairment in survivors at 18 months of age. Neurodevelopmental impairment will be defined as any of:

• Bayley mental developmental scale score less than 70

• Gross Motor Function Classification System Levels III – V

• Bilateral cortical visual impairments

Trial Registration

Current Controlled Trials ISRCTN89547571

Bench to bedside strategies for optimizing neuroprotection following perinatal hypoxia-ischaemia in high and low resource settings

BACKGROUND

Therapeutic hypothermia gathers impetus in the developed world as a safe and effective therapy for term asphyxial encephalopathy. Although many questions still remain about the optimal application of hypothermic neuroprotection it is difficult to ignore the developing world where the prevalence of asphyxial encephalopathy is much higher. Experimental studies to optimize high tech cooling need to run in parallel with trials to determine the possible benefits of therapeutic hypothermia in low resource settings.

METHODS

We used a validated newborn piglet model of transient HI to determine (i) whether optimal neuroprotection occurs at different temperatures in the cortical and deep grey matter; (ii) the effect of body size on regional brain temperature under normothermia and hypothermia; (iii) the effect of insult severity on the therapeutic window duration; (iv) whether cooling using a water bottle is feasible. In this model hypoxia-ischaemia is induced by reversible occlusion of the common carotid arteries by remotely controlled vascular occluders and simultaneous reduction in the inspired oxygen fraction to 0.12. Intensive care can be administered to the piglet maintaining metabolic and physiological homeostasis throughout the experiment, and cerebral energy metabolism is monitored continuously providing quantitative measures of the HI insult, latent phase and secondary energy failure using phosphorus-31 ((31)P) magnetic resonance spectroscopy (MRS).

RESULTS

(i) The optimal temperature for cooling was lower in the cortex than deep grey matter. (ii) Cerebral temperatures were body-weight dependent: a smaller body weight led to a lower brain temperature especially with selective head cooling. (iii) Latent-phase duration is inversely related to insult severity. (iv) Low tech, simple cooling methods using a water bottle can induce and maintain moderate hypothermia.

CONCLUSIONS

Small shifts in brain temperature critically influence the survival of neuronal cells and body size critically influences brain-temperature gradients - smaller subjects have a larger surface area to brain volume and hence more heat is lost. The clinical implication is that smaller infants may require higher cap or body temperatures to avoid detrimental effects of over-zealous cooling. Latent-phase brevity may explain less effective neuroprotection following severe HI in some clinical studies. "Tailored" treatments which take into account individual and regional characteristics may increase the effectiveness of therapeutic hypothermia in the developed world. Low tech cooling methods using water bottles may be feasible although adequate staffing and monitoring would be required.

Hypothermia

Experimental studies show that, following hypoxic ischaemic injury, mild induced hypothermia-a reduction of body temperature by about 3 degrees C -- preserves cerebral energy metabolism, reduces cerebral tissue injury and improves neurological function. Randomized trials in full-term and near-full-term newborns suggest that treatment with mild hypothermia is safe and improves survival without disabilities up to 18 months of age. Although the optimal time of initiation, the depth and duration, and the method of cooling are uncertain, in the absence of specific treatments many clinicians will wish to consider treating asphyxiated infants with hypothermia. Guidance now needs to be provided to promote uniform practice, to avoid inappropriate treatment and to foster continuing collaboration in future studies of neuroprotection following asphyxia. If the promising results of the current trials are confirmed by the findings from other on-going studies, with longer follow-up, the impact of such a treatment on the babies, their families and health resources in the shorter and longer terms will be considerable.

Comparative prognostic utilities of early quantitative magnetic resonance imaging spin-spin relaxometry and proton magnetic resonance spectroscopy in neonatal encephalopathy

OBJECTIVE

We sought to compare the prognostic utilities of early MRI spin-spin relaxometry and proton magnetic resonance spectroscopy in neonatal encephalopathy.

METHODS

Twenty-one term infants with neonatal encephalopathy were studied at a mean age of 3.1 days (range: 1-5). Basal ganglia, thalamic and frontal, parietal, and occipital white matter spin-spin relaxation times were determined from images with echo times of 25 and 200 milliseconds. Metabolite ratios were determined from an 8-mL thalamic-region magnetic resonance spectroscopy voxel (1H point-resolved spectroscopy; echo time 270 milliseconds). Outcomes were assigned at age 1 year as follows: (1) normal, (2) moderate (neuromotor signs or Griffiths developmental quotient of 75-84), (3) severe (functional neuromotor deficit or developmental quotient <75 or died). Predictive efficacies for differentiation between normal and adverse (combined moderate and severe) outcomes were compared by receiver operating characteristic curve analysis and logistic regression.

RESULTS

Thalamic and basal ganglia spin-spin relaxation times correlated positively with outcome and predicted adversity. Although thalamic and basal ganglia spin-spin relaxation times were prognostic of adversity, magnetic resonance spectroscopy metabolite ratios were better predictors, and, of these, lactate/N-acetylaspartate was most accurate.

CONCLUSIONS

Deep gray matter spin-spin relaxation time was increased in the first few days after birth in infants with an adverse outcome. Proton magnetic resonance spectroscopy was more prognostic than spin-spin relaxation time, with lactate/N-acetylaspartate the best measure. Nevertheless, both techniques were useful for early prognosis, and the potential superior spatial resolution of spin-spin relaxometry may define better the precise anatomic pattern of injury in the early days after birth.

N-methyl-isobutyl-amiloride ameliorates brain injury when commenced before hypoxia ischemia in neonatal mice

Underphysiologic conditions, brain intracellular pH (pH(i)) is maintained at 7.03. Rebound brain intracellular alkalosis has been observed in experimental models and adult stroke after hypoxia/ischemia (HI). In term infants with neonatal encephalopathy (NE), an association exists between the magnitude of brain alkalosis and neurodevelopmental outcome, and there is increasing evidence to suggest that alkalosis may be deleterious to cell survival. Activation of the Na(+)/H(+) exchanger (NHE) is thought to be responsible for the rapid normalization of pH(i) and rebound alkalosis after reperfusion. We hypothesized that N-methyl-isobutyl-amiloride (MIA), an inhibitor of the NHE, would reduce brain injury in a model of neonatal HI. Seven-day-old mice underwent left carotid artery occlusion followed by exposure to 8% oxygen for 30 min (moderate insult) or 1 h (severe insult). Animals received MIA or saline 8 hourly starting 30 min before HI. Outcome was determined at 48 h by measuring viable tissue in the injured hemisphere (severe insult) or injury score and TUNEL staining (moderate insult). After the severe insult, MIA had a significant neuroprotective effect increasing forebrain tissue survival from 44% to 67%. After the moderate insult, damage was localized to the hippocampus where treatment resulted in a significant reduction in injury score and in TUNEL-positive cells. MIA was also shown to have a significant overall neuroprotective effect based on injury score after the moderate insult. Amiloride analogues are neuroprotective when commenced before HI in a mouse model.

Advanced MR techniques in the term-born neonate with perinatal brain injury

Magnetic resonance imaging (MRI) has become an essential tool for assessing the neonatal brain. Conventional imaging can detect patterns of injury that relate to the aetiology and timing of an insult and provide valuable information about prognosis. Sequences must always be adapted for the immature brain. Diffusion techniques improve the detection of ischaemic tissue and allow more accurate timing of an insult. Diffusion tensor imaging allows the assessment of tissue microstructure changes with normal development as well as in response to tissue injury. Diffusion tractography will further our understanding of the long-term effects of perinatal injuries on brain development, and when used in combination with clinical and functional imaging studies will allow the plasticity of the immature brain to be studied. MR angiography and venography are important adjuncts to the clinical examination, and when combined with perfusion studies can provide valuable information about vessel development following injury. Detailed vascular studies may detect inherent susceptibilities, which give rise to lesions in some babies but not others. The future for neonatal imaging is exciting; however, detailed and serial imaging of carefully chosen cohorts of infants coupled with long-term clinical follow-up are essential to ensure the clinical significance of any new findings.

Time for a cool head-neuroprotection becomes a reality

Studies in encephalopathic infants have demonstrated a brief phase of normal cerebral energetics following hypoxia-ischaemia prior to development of delayed energy failure. In experimental models, mild hypothermia has shown a consistent neuroprotective action, although its efficacy is critically dependent on the severity of the primary insult, the delay in initiating cooling, and the duration and depth of hypothermia. Early electroencephalographic assessment of encephalopathic infants has the potential to provide objective information about the preceding insult, aiding the selection of infants for enrollment to clinical trials. Preliminary results from a large randomised trial of selective head cooling suggest that early intervention can lead to significantly improved outcome in a subgroup of encephalopathic infants with intermediate electroencephalographic abnormalities. Further research in established experimental models is essential to improve the identification of suitable infants for treatment, to investigate the importance of variations in regional brain temperature, and to examine the therapeutic potential of hypothermia combined with other neuroprotective agents.