Dramatic neuronal rescue with prolonged selective head cooling after ischemia in fetal lambs

Treatment temperature and insult severity influence the neuroprotective effects of therapeutic hypothermia

Therapeutic hypothermia (HT) is standard care for moderate and severe neonatal hypoxic-ischaemic encephalopathy (HIE), the leading cause of permanent brain injury in term newborns. However, the optimal temperature for HT is still unknown, and few preclinical studies have compared multiple HT treatment temperatures. Additionally, HT may not benefit infants with severe encephalopathy. In a neonatal rat model of unilateral hypoxia-ischaemia (HI), the effect of five different HT temperatures was investigated after either moderate or severe injury. At postnatal-day seven, rat pups underwent moderate or severe HI followed by 5 h at normothermia (37 °C), or one of five HT temperatures: 33.5 °C, 32 °C, 30 °C, 26 °C, and 18 °C. One week after treatment, neuropathological analysis of hemispheric and hippocampal area loss, and CA1 hippocampal pyramidal neuron count, was performed. After moderate injury, a significant reduction in hemispheric and hippocampal loss on the injured side, and preservation of CA1 pyramidal neurons, was seen in the 33.5 °C, 32 °C, and 30 °C groups. Cooling below 33.5 °C did not provide additional neuroprotection. Regardless of treatment temperature, HT was not neuroprotective in the severe HI model. Based on these findings, and previous experience translating preclinical studies into clinical application, we propose that milder cooling should be considered for future clinical trials.

Serum Lactate, Brain Magnetic Resonance Imaging and Outcome of Neonatal Hypoxic Ischemic Encephalopathy after Therapeutic Hypothermia

BACKGROUND

Serum lactate was used to predict the severity and outcome of neonatal hypoxic ischemic encephalopathy (HIE) before the era of therapeutic hypothermia (TH). There is no report on neurodevelopment (ND) outcome of neonates with HIE treated with TH in Taiwan.

METHODS

Between April 2011 and December 2012, newborn infants admitted to Chang Gung Memorial Hospital (CGMH), with gestational age > 35 weeks and birth weight ≥ 1800 g, who had acute perinatal events, evidence of significant fetal compromise, and ongoing clinical encephalopathy were prospectively enrolled for TH. Whole body cooling method was used to maintain the affected neonate's esophageal temperature at 33.5 ± 0.5 °C for 72 hours. Demographic data were recorded and hemogram, biochemical parameters, serum lactate, and creatine kinase (CK) were measured as well. Brain magnetic resonance imaging (MRI) was performed between 7 and 14 days of life. ND outcome of infants was evaluated by Bayley Scales of Infant Development, third edition (BSID-III) at 24 months of corrected age. Poor ND (PND) outcome was defined as infants surviving with either disability or ND delay.

RESULTS

Seventeen patients were enrolled. Fifty-nine percent of babies (10/17) were born through cesarean section and 77% of babies (13/17) were transferred from outside hospitals. Six babies were moderate HIE and 11 babies were severe HIE. Among the 14 surviving patients, eight infants had PND outcome. There was no difference in demographic data between infants with and without PND. Serum level of lactate (mg/dL) after 72 hours of TH was higher (35.6 vs. 13.8, p = 0.042) in infants with PND. Neonates with abnormal brain MRI findings were also associated with PND (p = 0.01).

CONCLUSION

This is the first report on ND outcome of neonates with HIE treated with TH in Taiwan. Higher serum level of lactate following TH and abnormal results of brain MRI are associated with poor ND outcome.

Non-additive effects of delayed connexin hemichannel blockade and hypothermia after cerebral ischemia in near-term fetal sheep

Hypothermia is partially neuroprotective after neonatal hypoxic-ischemic encephalopathy. Blockade of connexin hemichannels can improve recovery of brain activity and cell survival after ischemia in near-term fetal sheep. In this study, we investigated whether combining delayed hypothermia with connexin hemichannel blockade with intracerebroventricular infusion of a mimetic peptide can further improve outcomes after cerebral ischemia. Fetal sheep (0.85 gestation) received 30 minutes of cerebral ischemia followed by a 3-hour recovery period before treatment was started. Fetuses were randomized to one of the following treatment groups: normothermia (n=8), hypothermia for 3 days (n=8), connexin hemichannel blockade (50 μmol/L intracerebroventricular over 1 hour followed by 50 μmol/L over 24 hours, n=8) or hypothermia plus hemichannel blockade (n=7). After 7 days recovery, hypothermia was associated with reduced seizure burden, improved electroencephalographic (EEG) power, and a significant increase in neuronal and oligodendrocyte survival and reduced induction of Iba1-positive microglia. In contrast, although hemichannel blockade reduced seizure burden, there was no effect on EEG power or histology (P<0.05). There was no further improvement in outcomes with combined hypothermia plus hemichannel blockade. In conclusion, these data show that there is no additive neuroprotection with combined hypothermia and hemichannel blockade after cerebral ischemia in near-term fetal sheep.

Dietary interventions designed to protect the perinatal brain from hypoxic-ischemic encephalopathy--Creatine prophylaxis and the need for multi-organ protection

Birth asphyxia or hypoxia arises from impaired placental gas exchange during labor and remains one of the leading causes of neonatal morbidity and mortality worldwide. It is a condition that can strike in pregnancies that have been uneventful until these final moments, and leads to fundamental loss of cellular energy reserves in the newborn. The cascade of metabolic changes that occurs in the brain at birth as a result of hypoxia can lead to significant damage that evolves over several hours and days, the severity of which can be ameliorated with therapeutic cerebral hypothermia. However, this treatment is only applied to a subset of newborns that meet strict inclusion criteria and is usually administered only in facilities with a high level of medical surveillance. Hence, a number of neuropharmacological interventions have been suggested as adjunct therapies to improve the efficacy of hypothermia, which alone improves survival of the post-hypoxic infant but does not altogether prevent adverse neurological outcomes. In this review we discuss the prospect of using creatine as a dietary supplement during pregnancy and nutritional intervention that can significantly decrease the risk of brain damage in the event of severe oxygen deprivation at birth. Because brain damage can also arise secondarily to compromise of other fetal organs (e.g., heart, diaphragm, kidney), and that compromise of mitochondrial function under hypoxic conditions may be a common mechanism leading to damage of these tissues, we present data suggesting that dietary creatine supplementation during pregnancy may be an effective prophylaxis that can protect the fetus from the multi-organ consequences of severe hypoxia at birth.

Subacute Hypoxia-Ischemia and the Timing of Injury in Treatment With Therapeutic Hypothermia

OBJECTIVE

This study aims to categorize infants treated with therapeutic hypothermia who presented with suspected subacute hypoxia-ischemia-that is, injury that likely occurred well before delivery and thus beyond the 6-hour window for therapeutic hypothermia-and to contrast the clinical characteristics with infants who suffered a known acute hypoxia-ischemia event.

DESIGN

A retrospective chart review was undertaken of infants treated with therapeutic hypothermia at our center during a 6-year period. Suspected subacute injury is defined as decreased fetal movement greater than 6 hours before delivery or severe depression at birth without need for cardiopulmonary resuscitation. Acute injury is defined as an acute perinatal event including placental abruption, ruptured uterus, or umbilical cord abnormalities. Abnormal outcome is defined as death, cognitive delay, or spastic quadriplegia at follow-up.

RESULTS

Infants with subacute (n = 7) versus acute injury (n = 26) were less likely to require cardiopulmonary resuscitation, were less acidotic at birth on cord gases with no significant difference in initial postnatal pH or base deficit, were more severely encephalopathic with severe amplitude electroencephalogram suppression, and demonstrated universal adverse outcome.

CONCLUSIONS

These data demonstrate greater benefit of therapeutic hypothermia for those infants with acute versus subacute injury. Early initiation of therapeutic hypothermia relative to the presumed onset of hypoxia-ischemia is critical. Early severe encephalopathy in the absence of a known acute perinatal event should raise concern in some cases for a subacute insult where the effect of therapeutic hypothermia is unlikely to be of benefit.

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

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

Ontogeny of tight junction protein expression in the ovine cerebral cortex during development

Tight junctions of the blood-brain barrier are composed of transmembrane and associated cytoplasmic proteins. The transmembrane claudin proteins form the primary seal between endothelial cells and junctional adhesion molecules (JAMs) regulate tight junction formation. We have previously shown that claudin-1, claudin-5, zonula occludens (ZO)-1, and ZO-2 exhibit differential developmental regulation from 60% of gestation up to maturity in adult sheep. The purpose of the current study was to examine developmental changes in claudin-3, -12, and JAM-A protein expression in cerebral cortices of fetuses at 60%, 80%, and 90% gestation, and in newborn and adult sheep. We also examined correlations between changes in endogenous cortisol levels and tight junction protein expression in cerebral cortices of the fetuses. Claudin-3, -12 and JAM-A expressions were determined by Western immunoblot. Claudin-3 and -12 were lower (P<0.01) at 60%, 80%, 90% and in newborns than in adults, and JAM-A was lower in adults than in fetuses at 80% and 90% gestation. Claudin-3 expression demonstrated a direct correlation with increasing plasma cortisol levels (r=0.60, n=15, P<0.02) in the fetuses. We conclude that: claudin-3, -12 and JAM-A are expressed as early as 60% of gestation in ovine cerebral cortices, exhibit differential developmental regulation, and that increasing endogenous glucocorticoids modulate claudin-3 expression in the fetus.

Therapeutic Hypothermia for Neonatal Hypoxic-Ischemic Encephalopathy - Where to from Here?

Hypoxia-ischemia before or around the time of birth occurs in approximately 2/1000 live births and is associated with a high risk of death or lifelong disability. Therapeutic hypothermia is now well established as standard treatment for infants with moderate to severe hypoxic-ischemic encephalopathy but is only partially effective. There is compelling preclinical and clinical evidence that hypothermia is most protective when it is started as early as possible after hypoxia-ischemia. Further improvements in outcome from therapeutic hypothermia are very likely to arise from strategies to reduce the delay before starting treatment of affected infants. In this review, we examine evidence that current protocols are reasonably close to the optimal depth and duration of cooling, but that the optimal rate of rewarming after hypothermia is unclear. The potential for combination treatments to augment hypothermic neuroprotection has considerable promise, particularly with endogenous targets such as melatonin and erythropoietin, and noble gases such as xenon. We dissect the critical importance of preclinical studies using realistic delays in treatment and clinically relevant cooling protocols when examining combination treatment, and that for many strategies overlapping mechanisms of action can substantially attenuate any effects.

The hospital outcomes compared between the early and late hypothermia-treated groups in neonates

BACKGROUND AND OBJECTIVE

The incidence of hypoxic ischemic encephalopathy (HIE) in developed countries is estimated to be 1.5 per 1000 live births. The primary aim of this study was to analyze whether earlier hypothermia (≤1 h) improves hospital outcomes in survivors who underwent therapeutic hypothermia (TH) when compared with late TH (>1 h).

METHOD

Forty-nine (70%) newborns received TH for 72 h, within 6 h of birth; the remaining 21 received standard care. We divided the TH-treated newborns into early and late groups; early cooling was considered when TH was started ≤1 h after birth; late cooling was considered when started >1 h.

RESULTS

The early TH group consisted of 20 of 49 (41%) infants; the late TH group consisted of 29 (59%) infants. Apgar score at 1 min and the initial calcium level was significantly lower in the early (≤1 h) TH infants; there were significantly more inborns in the early TH group (p = 0.008). Infants in the late TH group manifested more clinical seizures followed by more abnormal EEG findings, longer ventilator care and longer hospitalization (p = 0.001). TH-related complications and mortality were not significantly different between the two groups.

CONCLUSIONS

Early TH (≤1 h) had lower Apgar score at 1 min and initial calcium level, but had decreased incidence of clinico-electrical seizures among HIE infants. Also, ventilator support and hospitalization period were longer in the late TH group.

Development of an experimental model of maternal allergic asthma during pregnancy

Maternal asthma during pregnancy adversely affects pregnancy outcomes but identification of the cause/s, and the ability to evaluate interventions, is limited by the lack of an appropriate animal model. We therefore aimed to characterise maternal lung and cardiovascular responses and fetal-placental growth and lung surfactant levels in a sheep model of allergic asthma. Immune and airway functions were studied in singleton-bearing ewes, either sensitised before pregnancy to house dust mite (HDM, allergic, n = 7) or non-allergic (control, n = 5), and subjected to repeated airway challenges with HDM (allergic group) or saline (control group) throughout gestation. Maternal lung, fetal and placental phenotypes were characterised at 140 ± 1 days gestational age (term, ∼147 days). The eosinophil influx into lungs was greater after HDM challenge in allergic ewes than after saline challenge in control ewes before mating and in late gestation. Airway resistance increased throughout pregnancy in allergic but not control ewes, consistent with increased airway smooth muscle in allergic ewes. Maternal allergic asthma decreased relative fetal weight (-12%) and altered placental phenotype to a more mature form. Expression of surfactant protein B mRNA was 48% lower in fetuses from allergic ewes than controls, with a similar trend for surfactant protein D. Thus, allergic asthma in pregnant sheep modifies placental phenotype, and inhibits fetal growth and lung development consistent with observations from human pregnancies. Preconceptional allergen sensitisation and repeated airway challenges in pregnant sheep therefore provides an animal model to identify mechanisms of altered fetal development and adverse pregnancy outcomes caused by maternal asthma in pregnancy.

Therapeutic hypothermia and hypoxia-ischemia in the term-equivalent neonatal rat: characterization of a translational preclinical model

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is a major cause of morbidity in survivors. Therapeutic hypothermia (TH) is the only available intervention, but the protection is incomplete. Preclinical studies of HIE/TH in the rodent have relied on the postnatal day (P) 7 rat whose brain approximates a 32-36 wk gestation infant, less relevant for these studies. We propose that HIE and TH in the term-equivalent P10 rat will be more translational.

METHODS

P10-11 rat pups were subjected to unilateral hypoxia-ischemia (HI) and 4 h recovery in normothermic (N) or hypothermic (TH) conditions. Brain damage was assessed longitudinally at 24 h, 2 wk, and 12 wk. Motor function was assessed with the beam walk; recognition memory was measured by novel object recognition.

RESULTS

Neuroprotection with TH was apparent at 2 and 12 wk in both moderately and severely damaged animals. TH improved motor function in moderate, but not severe, damage. Impaired object recognition occurred with severe damage with no evidence of protection of TH.

CONCLUSION

This adaptation of the immature rat model of HI provides a reproducible platform to further study HIE/TH in which individual animals are followed up longitudinally to provide a useful translational preclinical model.

Interleukin-1β transfer across the blood-brain barrier in the ovine fetus

Pro-inflammatory cytokines contribute to hypoxic-ischemic brain injury. Blood-brain barrier (BBB) dysfunction represents an important component of hypoxic-ischemic brain injury in the fetus. Hypoxic-ischemic injury could accentuate systemic cytokine transfer across the fetal BBB. There has been considerable conjecture suggesting that systemic cytokines could cross the BBB during the perinatal period. Nonetheless, evidence to support this contention is sparse. We hypothesized that ischemia-reperfusion increases the transfer of systemic interleukin-1β (IL-1β) across the BBB in the fetus. Ovine fetuses at 127 days of gestation were studied 4 hours after 30 minutes of bilateral carotid artery occlusion and compared with a nonischemic group. Recombinant ovine IL-1β protein was expressed from an IL-1β pGEX-2 T vector in E. coli BL-21 cells and purified. The BBB function was quantified in 12 brain regions using a blood-to-brain transfer constant with intravenous (125)I-radiolabeled IL-1β ((125)I-IL-1β). Interleukin-1β crossed the intact BBB in nonischemic fetuses. Blood-to-brain transport of (125)I-IL-1β was higher (P<0.05) across brain regions in fetuses exposed to ischemia-reperfusion than nonischemic fetuses. We conclude that systemic IL-1β crosses the intact fetal BBB, and that ischemia-reperfusion increases transfer of this cytokine across the fetal BBB. Therefore, altered BBB function after hypoxia-ischemia facilitates entry of systemic cytokines into the brain of the fetus.

Neonatal encephalopathy: pre-clinical studies in neuroprotection

Neonatal encephalopathy resulting from HI (hypoxia-ischaemia) continues to be a significant cause of mortality and morbidity in infants and children, affecting 1-2/1000 live term births and up to 60% of pre-term births. In order to understand the pathophysiology of this insult, as well as design therapeutic interventions, it is important to establish a relevant animal model for pre-clinical studies. One of the most frequently used models of HI-induced brain damage in immature animals is the unilateral carotid ligation/hypoxia model, initially developed in our laboratory more than 30 years ago. The original model employed the postnatal day 7 rat, whose brain is representative of that of a late gestation, pre-term [32-36 weeks GA (gestational age)] human infant. We, and others, have employed this model to characterize the pathophysiological, biochemical/energetic and neuropathological events following HI, as well as the determination of the unique characteristics of the immature brain that define its vulnerability to, and outcome from, HI. In defining the cascade of events following HI, it has become possible to identify potential targets for intervention and neuroprotection. Currently, the only available therapeutic intervention for neonatal encephalopathy in the term asphyxiated infant is therapeutic hypothermia, although this must be initiated within 6 h of birth and is at best partially effective in moderately injured infants. Ongoing pre-clinical studies are necessary to determine the basis for the partial protection afforded by hypothermia as well as the design of adjunct therapies to improve the outcome. The present review highlights the importance of using a well-characterized and relevant animal model to continue to pursue translational research in neuroprotection for the infant brain.

Adding 5 h delayed xenon to delayed hypothermia treatment improves long-term function in neonatal rats surviving to adulthood

BACKGROUND

We previously reported that combining immediate hypothermia with immediate or 2 h delayed inhalation of an inert gas, xenon, gave additive neuroprotection in rats after a hypoxic-ischemic insult, compared to hypothermia alone. Defining the therapeutic time window for this new combined intervention is crucial in clinical practice when immediate treatment is not always feasible. The aim of this study is to investigate whether combined hypothermia and xenon still provide neuroprotection in rats after a 5 h delay for both hypothermia and xenon.

METHODS

Seven-day-old Wistar rat pups underwent a unilateral hypoxic-ischemic insult. Pups received 5 h of treatment starting 5 h after the insult randomized between normothermia, hypothermia, or hypothermia with 50% xenon. Surviving pups were tested for fine motor function through weeks 8-10 before being euthanized at week 11. Their hemispheric and hippocampal areas were assessed.

RESULTS

Both delayed hypothermia-xenon and hypothermia-only treated groups had significantly less brain tissue loss than those which underwent normothermia. The functional performance after 1 wk and adulthood was significantly better after hypothermia-xenon treatment as compared to the hypothermia-only or normothermia groups.

CONCLUSION

Adding 50% xenon to 5 h delayed hypothermia significantly improved functional outcome as compared to delayed hypothermia alone despite similar reductions in brain area.

In vivo Monitoring of Cerebral Hemodynamics in the Immature Rat: Effects of Hypoxia-Ischemia and Hypothermia

BACKGROUND

Neonatal hypoxic-ischemic (HI) encephalopathy occurs in 1-4 per 1,000 live term births and can cause devastating neurodevelopmental disabilities. Currently, therapeutic hypothermia (TH) is the only treatment with proven efficacy. Since TH is associated with decreased cerebral metabolism and cerebral blood flow (CBF), it is important to assess CBF at the bedside. Diffuse correlation spectroscopy (DCS) has emerged as a promising optical modality to noninvasively assess an index of CBF (CBFi) in both humans and animals. In this initial descriptive study, we employ DCS to monitor the evolution of CBFi following HI with or without TH in immature rats. We investigate potential relationships between CBF and subsequent cerebral damage.

METHODS

HI was induced on postnatal day 10 or 11 rat pups by right common carotid artery ligation followed by 60-70 min hypoxia (8% oxygen). After HI, the pups recovered for 4 h under hypothermia (HI-TH group, n = 23) or normothermia (HI-N group, n = 23). Bilateral measurements of hemispheric CBFi were made with DCS in unanesthetized animals at baseline, before HI, and 0, 1, 2, 3, 4, 5, and 24 h after HI. The animals were sacrificed at either 1 or 4 weeks, and brain injury was scored on an ordinal scale of 0-5 (0 = no injury).

RESULTS

Carotid ligation caused moderate bilateral decreases in CBFi. Following HI, an initial hyperemia was observed that was more prominent in the contralateral hemisphere. After initiation of TH, CBFi dropped significantly below baseline levels and remained reduced for the duration of TH. In contrast, CBFi in the HI-N group was not significantly decreased from baseline levels. Reductions in CBFi after 4 h of TH were not associated with reduced damage at 1 or 4 weeks. However, elevated ipsilateral CBFi and ipsilateral-to-contralateral CBFi ratios at 24 h were associated with worse outcome at 1 week after HI.

CONCLUSIONS

Both HI and TH alter CBFi, with significant differences in CBFi between hypothermic and normothermic groups after HI. CBFi may be a useful biomarker of subsequent cerebral damage.

How long is too long for cerebral cooling after ischemia in fetal sheep?

Therapeutic hypothermia can partially reduce long-term death and disability in neonates after hypoxic-ischemic encephalopathy. The aim of this study was to determine whether prolonging the duration of cooling from 3 days to 5 days could further improve outcomes of cerebral ischemia in near-term fetal sheep. Fetal sheep (0.85 gestation) received 30 minutes bilateral carotid artery occlusion followed by 3 days of normothermia (n = 8), 3 days of hypothermia (n = 8), or 5 days of hypothermia (n=8) started 3 hours after ischemia. Sham controls received sham ischemia followed by normothermia (n = 8). Cerebral ischemia was associated with profound loss of electroencephalography power and spectral edge, with greater and more rapid recovery in both hypothermia groups (P<0.05). Ischemia was associated with severe loss of neurons in the cortex, hippocampus and thalamus (P < 0.05), with a significant improvement in both hypothermia groups. However, the ischemia-3-day hypothermia group showed greater neuronal survival in the cortex and dentate gyrus compared with ischemia-5-day hypothermia (P < 0.05). Ischemia was associated with induction of iba1-positive microglia, which was attenuated in both hypothermia groups (P < 0.05). Extending the duration of delayed therapeutic hypothermia from 3 to 5 days did not improve outcomes after severe ischemia, and was associated with reduced neuronal survival in some regions.

A randomized clinical trial of therapeutic hypothermia mode during transport for neonatal encephalopathy

OBJECTIVE

To determine if temperature regulation is improved during neonatal transport using a servo-regulated cooling device when compared with standard practice.

STUDY DESIGN

We performed a multicenter, randomized, nonmasked clinical trial in newborns with neonatal encephalopathy cooled during transport to 9 neonatal intensive care units in California. Newborns who met institutional criteria for therapeutic hypothermia were randomly assigned to receive cooling according to usual center practices vs device servo-regulated cooling. The primary outcome was the percentage of temperatures in target range (33°-34°C) during transport. Secondary outcomes included percentage of newborns reaching target temperature any time during transport, time to target temperature, and percentage of newborns in target range 1 hour after cooling initiation.

RESULTS

One hundred newborns were enrolled: 49 to control arm and 51 to device arm. Baseline demographics did not differ with the exception of cord pH. For each subject, the percentage of temperatures in the target range was calculated. Infants cooled using the device had a higher percentage of temperatures in target range compared with control infants (median 73% [IQR 17-88] vs 0% [IQR 0-52], P < .001). More subjects reached target temperature during transport using the servo-regulated device (80% vs 49%, P <.001), and in a shorter time period (44 ± 31 minutes vs 63 ± 37 minutes, P = .04). Device-cooled infants reached target temperature by 1 hour with greater frequency than control infants (71% vs 20%, P < .001).

CONCLUSIONS

Cooling using a servo-regulated device provides more predictable temperature management during neonatal transport than does usual care for outborn newborns with neonatal encephalopathy.

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.

Human Umbilical Cord Blood Cells Ameliorate Motor Deficits in Rabbits in a Cerebral Palsy Model

Cerebral palsy (CP) has a significant impact on both patients and society, but therapy is limited. Human umbilical cord blood cells (HUCBC), containing various stem and progenitor cells, have been used to treat various brain genetic conditions. In small animal experiments, HUCBC have improved outcomes after hypoxic-ischemic (HI) injury. Clinical trials using HUCBC are underway, testing feasibility, safety and efficacy for neonatal injury as well as CP. We tested HUCBC therapy in a validated rabbit model of CP after acute changes secondary to HI injury had subsided. Following uterine ischemia at 70% gestation, we infused HUCBC into newborn rabbit kits with either mild or severe neurobehavioral changes. Infusion of high-dose HUCBC (5 × 10(6) cells) dramatically altered the natural history of the injury, alleviating the abnormal phenotype including posture, righting reflex, locomotion, tone, and dystonia. Half the high dose showed lesser but still significant improvement. The swimming test, however, showed that joint function did not restore to naïve control function in either group. Tracing HUCBC with either MRI biomarkers or PCR for human DNA found little penetration of HUCBC in the newborn brain in the immediate newborn period, suggesting that the beneficial effects were not due to cellular integration or direct proliferative effects but rather to paracrine signaling. This is the first study to show that HUCBC improve motor performance in a dose-dependent manner, perhaps by improving compensatory repair processes.

Magnesium is not consistently neuroprotective for perinatal hypoxia-ischemia in term-equivalent models in preclinical studies: a systematic review

There is an important unmet need to further improve the outcome of neonatal encephalopathy in term infants. Meta-analyses of large controlled trials now suggest that maternal magnesium sulfate (MgSO4) therapy is associated with a reduced risk of cerebral palsy and gross motor dysfunction after premature birth, but that it has no effect on death or disability. Because of this inconsistency, it remains controversial whether MgSO4 is clinically neuroprotective and, thus, it is unclear whether it would be appropriate to test MgSO4 for treatment of encephalopathy in term infants. We therefore systematically reviewed the preclinical evidence for neuroprotection with MgSO4 before or after hypoxic-ischemic encephalopathy (HIE) in term-equivalent perinatal and adult animals. The outcomes were highly inconsistent between studies. Although there were differences in dose and timing of administration, there was evidence that beneficial effects of MgSO4 were associated with confounding mild hypothermia and, strikingly, the studies that included rigorous maintenance of environmental temperature or body temperature consistently suggested a lack of effect. On balance, these preclinical studies suggest that peripherally administered MgSO4 is unlikely to be neuroprotective. Rigorous testing in translational animal models of perinatal HIE is needed before MgSO4 should be considered in clinical trials for encephalopathy in term infants.

Anti-IL-6 neutralizing antibody modulates blood-brain barrier function in the ovine fetus

Impaired blood-brain barrier function represents an important component of hypoxic-ischemic brain injury in the perinatal period. Proinflammatory cytokines could contribute to ischemia-related blood-brain barrier dysfunction. IL-6 increases vascular endothelial cell monolayer permeability in vitro. However, contributions of IL-6 to blood-brain barrier abnormalities have not been examined in the immature brain in vivo. We generated pharmacologic quantities of ovine-specific neutralizing anti-IL-6 mAbs and systemically infused mAbs into fetal sheep at 126 days of gestation after exposure to brain ischemia. Anti-IL-6 mAbs were measured by ELISA in fetal plasma, cerebral cortex, and cerebrospinal fluid, blood-brain barrier permeability was quantified using the blood-to-brain transfer constant in brain regions, and IL-6, tight junction proteins, and plasmalemma vesicle protein (PLVAP) were detected by Western immunoblot. Anti-IL-6 mAb infusions resulted in increases in mAb (P < 0.05) in plasma, brain parenchyma, and cerebrospinal fluid and decreases in brain IL-6 protein. Twenty-four hours after ischemia, anti-IL-6 mAb infusions attenuated ischemia-related increases in blood-brain barrier permeability and modulated tight junction and PLVAP protein expression in fetal brain. We conclude that inhibiting the effects of IL-6 protein with systemic infusions of neutralizing antibodies attenuates ischemia-related increases in blood-brain barrier permeability by inhibiting IL-6 and modulates tight junction proteins after ischemia.

Neuroprotection in preterm infants

Preterm infants born before the 30th week of pregnancy are especially at risk of perinatal brain damage which is usually a result of cerebral ischemia or an ascending intrauterine infection. Prevention of preterm birth and early intervention given signs of imminent intrauterine infection can reduce the incidence of perinatal cerebral injury. It has been shown that administering magnesium intravenously to women at imminent risk of a preterm birth leads to a significant reduction in the likelihood of the infant developing cerebral palsy and motor skill dysfunction. It has also been demonstrated that delayed clamping of the umbilical cord after birth reduces the rate of brain hemorrhage among preterm infants by up to 50%. In addition, mesenchymal stem cells seem to have significant neuroprotective potential in animal experiments, as they increase the rate of regeneration of the damaged cerebral area. Clinical tests of these types of therapeutic intervention measures appear to be imminent. In the last trimester of pregnancy, the serum concentrations of estradiol and progesterone increase significantly. Preterm infants are removed abruptly from this estradiol and progesterone rich environment. It has been demonstrated in animal experiments that estradiol and progesterone protect the immature brain from hypoxic-ischemic lesions. However, this neuroprotective strategy has unfortunately not yet been subject to sufficient clinical investigation.

Neutralizing anti-interleukin-1β antibodies modulate fetal blood-brain barrier function after ischemia

We have previously shown that increases in blood-brain barrier permeability represent an important component of ischemia-reperfusion related brain injury in the fetus. Pro-inflammatory cytokines could contribute to these abnormalities in blood-brain barrier function. We have generated pharmacological quantities of mouse anti-ovine interleukin-1β monoclonal antibody and shown that this antibody has very high sensitivity and specificity for interleukin-1β protein. This antibody also neutralizes the effects of interleukin-1β protein in vitro. In the current study, we hypothesized that the neutralizing anti-interleukin-1β monoclonal antibody attenuates ischemia-reperfusion related fetal blood-brain barrier dysfunction. Instrumented ovine fetuses at 127 days of gestation were studied after 30 min of carotid occlusion and 24h of reperfusion. Groups were sham operated placebo-control- (n=5), ischemia-placebo- (n=6), ischemia-anti-IL-1β antibody- (n=7), and sham-control antibody- (n=2) treated animals. Systemic infusions of placebo (0.154M NaCl) or anti-interleukin-1β monoclonal antibody (5.1±0.6 mg/kg) were given intravenously to the same sham or ischemic group of fetuses at 15 min and 4h after ischemia. Concentrations of interleukin-1β protein and anti-interleukin-1β monoclonal antibody were measured by ELISA in fetal plasma, cerebrospinal fluid, and parietal cerebral cortex. Blood-brain barrier permeability was quantified using the blood-to-brain transfer constant (Ki) with α-aminoisobutyric acid in multiple brain regions. Interleukin-1β protein was also measured in parietal cerebral cortices and tight junction proteins in multiple brain regions by Western immunoblot. Cerebral cortical interleukin-1β protein increased (P<0.001) after ischemia-reperfusion. After anti-interleukin-1β monoclonal antibody infusions, plasma anti-interleukin-1β monoclonal antibody was elevated (P<0.001), brain anti-interleukin-1β monoclonal antibody levels were higher (P<0.03), and interleukin-1β protein concentrations (P<0.03) and protein expressions (P<0.001) were lower in the monoclonal antibody-treated group than in placebo-treated-ischemia-reperfusion group. Monoclonal antibody infusions attenuated ischemia-reperfusion-related increases in Ki across the brain regions (P<0.04), and Ki showed an inverse linear correlation (r= -0.65, P<0.02) with anti-interleukin-1β monoclonal antibody concentrations in the parietal cortex, but had little effect on tight junction protein expression. We conclude that systemic anti-interleukin-1β monoclonal antibody infusions after ischemia result in brain anti-interleukin-1β antibody uptake, and attenuate ischemia-reperfusion-related interleukin-1β protein up-regulation and increases in blood-brain barrier permeability across brain regions in the fetus. The pro-inflammatory cytokine, interleukin-1β, contributes to impaired blood-brain barrier function after ischemia in the fetus.

Hypothermia in hypoxic ischemic encephalopathy: a 5-year experience at Phoenix Children's Hospital Neuro NICU

We found TH to be safe and effective in improving survival and neurodevelopmental outcomes following HIE in term children. Additionally, the use of a multidisciplinary team involved with these complex patients and the use of advanced monitoring techniques will likely assist in identifying second insults (ie, seizures), leading to more rapidly instituted treatments. Our study, however, had the limitation of including only retrospective data from patients in whom TH was provided. This makes it difficult to identify the specific sources for the improved outcomes and/or the presence of complications.

Changes in amplitude-integrated electroencephalograms in piglets during selective mild head cooling after hypoxia-ischemia

BACKGROUND

Amplitude-integrated electroencephalogram (aEEG) is a simplified, alternative means of monitoring cerebral function and may be more useful clinically in some situations than conventional EEG. The aim of this study is to evaluate newborn piglets as an animal model to examine the effect of selective mild head cooling (HC) on aEEG after hypoxia-ischemia (HI).

METHODS

Thirty-four piglets were randomly allocated to the following treatment groups: normothermic control group (NC, n = 7), selective HC control group (HC, n = 9), normothermic HI group (NHI, n = 9), and selective HC HI group (SHC-HI, n = 9). HI was induced by temporary occlusion of both carotid arteries and simultaneous reduction of the concentration of inspired oxygen to 6% for 30 minutes. Mild hypothermia (35°C) was induced after HI using a HC cap and was maintained for 24 hours. Changes in aEEG were monitored for 6 days after these treatments and the incidence of abnormalities analyzed. Physiological parameters were also measured during this period.

RESULTS

In the two HI groups, animals exhibited severely abnormal aEEGs [continuous low voltage (CLV), burst-suppression, or flat tracing (FT)] 20 minutes after the beginning of HI. At 2 hours, the aEEG returned to normal in most of these animals. From 12 hours to 6 days, all animals in the NHI group exhibited severely abnormal aEEGs. Fewer animals in the SHC-HI group exhibited severe abnormal aEEGs during this time period, and four out of nine (44.4%) animals had continuous normal voltage (CNV) at 6 days.

CONCLUSIONS

Selective mild HC decreases the incidence of severe abnormal aEEGs at late times after HI in newborn piglets.

Obstetric antecedents to body-cooling treatment of the newborn infant

OBJECTIVE

Obstetric antecedents were analyzed in births in which the infant received whole-body cooling for neonatal encephalopathy.

STUDY DESIGN

This retrospective cohort study included all live-born singleton infants delivered at or beyond 36 weeks' gestation from October 2005 through December 2011. Infants who had received whole-body cooling identified by review of a prospective neonatal registry were compared with a control group comprising the remaining obstetric population delivered at greater than 36 weeks but not cooled. Univariable analysis was followed up by a staged, stepwise selection of variables with the intent to rank significant risk factors for cooling.

RESULTS

A total of 86,371 women delivered during the study period and 98 infants received whole-body cooling (1.1 per 1000 live births). Of these 98 infants, 80 newborns (88%) had moderate encephalopathy and 10 (12%) had severe encephalopathy prior to cooling. Maternal age of 15 years or younger, low parity, maternal body habitus (body mass index of ≥40 kg/m(2)), diabetes, preeclampsia, induction, epidural analgesia, chorioamnionitis, length of labor, and mode of delivery were associated with significantly increased risk of infant cooling during a univariable analysis. Catastrophic events to include umbilical cord prolapse (odds ratio [OR], 14; 95% confidence interval [CI], 3-72), placental abruption (OR, 17; 95% CI, 7-44), uterine rupture (OR, 130; 95% CI, 11-1477) were the strongest factors associated with infant cooling after staged-stepwise logistic analysis.

CONCLUSION

A variety of intrapartum characteristics were associated with infant cooling for neonatal encephalopathy, with the most powerful antecedents being umbilical cord prolapse, placental abruption, and uterine rupture.

Effects of inter-alpha inhibitor proteins on neonatal brain injury: Age, task and treatment dependent neurobehavioral outcomes

Hypoxic-ischemic (HI) brain injury is frequently associated with premature and/or full term birth related complications. HI injury often results in learning and processing deficits that reflect widespread damage to an extensive range of cortical and sub-cortical brain structures. Further, inflammation has been implicated in the long-term progression and severity of HI injury. Recently, inter-alpha inhibitor proteins (IAIPs) have been shown to attenuate inflammation in models of systemic infection. Importantly, preclinical studies of neonatal HI injury and neuroprotection often focus on single time windows of assessment or single behavioral domains. This approach limits translational validity, given evidence for a diverse spectrum of neurobehavioral deficits that may change across developmental windows following neonatal brain injury. Therefore, the aims of this research were to assess the effects of human IAIPs on early neocortical cell death (72h post-insult), adult regional brain volume measurements (cerebral cortex, hippocampus, striatum, corpus callosum) and long-term behavioral outcomes in juvenile (P38-50) and adult (P80+) periods across two independent learning domains (spatial and non-spatial learning), after postnatal day 7 HI injury in rats. Here, for the first time, we show that IAIPs reduce acute neocortical neuronal cell death and improve brain weight outcome 72h following HI injury in the neonatal rat. Further, these longitudinal studies are the first to show age, task and treatment dependent improvements in behavioral outcome for both spatial and non-spatial learning following systemic administration of IAIPs in neonatal HI injured rats. Finally, results also show sparing of brain regions critical for spatial and non-spatial learning in adult animals treated with IAIPs at the time of injury onset. These data support the proposal that inter-alpha inhibitor proteins may serve as novel therapeutics for brain injury associated with premature birth and/or neonatal brain injury and highlight the importance of assessing multiple ages, brain regions and behavioral domains when investigating experimental treatment efficacy.

Ischemia/Reperfusion-induced neovascularization in the cerebral cortex of the ovine fetus

Information on the effects of injury on neovascularization in the immature brain is limited. We investigated the effects of ischemia on cerebral cortex neovascularization after the exposure of fetuses to 30 minutes of cerebral ischemia followed by 48 hours of reperfusion (I/R-48), 30 minutes of cerebral ischemia followed by 72 hours of reperfusion (I/R-72), or sham control treatment (Non-I/R). Immunohistochemical and morphometric analyses of cerebral cortex sections included immunostaining for glial fibrillary acidic protein and collagen type IV (a molecular component of the vascular basal lamina) to determine the glial vascular network in fetal brains and Ki67 as a proliferation marker. Cerebral cortices from I/R-48 and I/R-72 fetuses exhibited general responses to ischemia, including reactive astrocyte morphology, which was not observed in Non-I/R fetuses. Cell bodies of reactive proliferating astrocytes, along with large end-feet, surrounded the walls of cerebral cortex microvessels in addition to the thick collagen type IV-enriched basal lamina. Morphometric analysis of the Non-I/R group with the I/R-48 and I/R-72 groups revealed increased collagen type IV density in I/R-72 cerebral cortex microvessels (p < 0.01), which also frequently displayed a sprouting appearance characterized by growing tip cells and activated pericytes. Increases in cerebral cortex basic fibroblast growth factor were associated with neovascularization. We conclude that increased neovascularization in fetal cerebral cortices occurs within 72 hours of ischemia.

Maternal treatment with glucocorticoids modulates gap junction protein expression in the ovine fetal brain

Gap junctions facilitate intercellular communication and are important in brain development. Connexins (Cx) comprise a transmembrane protein family that forms gap junctions. Cx-32 is expressed in oligodendrocytes and neurons, Cx-36 in neurons, and Cx-43 in astrocytes. Although single antenatal steroid courses are recommended for fetal lung maturation, multiple courses can be given to women at recurrent risk for premature delivery. We examined the effects of single and multiple glucocorticoid courses on Cx-32, Cx-36, and Cx-43 protein expressions in the fetal cerebral cortex, cerebellum, and spinal cord, and differences in Cx expression among brain regions under basal conditions. In the single-course groups, the ewes received dexamethasone (6 mg) or placebo as four intramuscular injections every 12h over 48 h. In the multiple-course groups, the ewes received the same treatment, once a week for 5 weeks starting at 76-78 days of gestation. Cx were measured by Western immunoblot on brain samples from 105 to 108-day gestation fetuses. A single dexamethasone course was associated with increases (P<0.05) in cerebral cortical and spinal cord Cx-36 and Cx-43 and multiple courses with increases in cerebellar and spinal cord Cx-36, and cerebral cortical and cerebellar Cx-43. Cx-32 did not change. Cx-32 was higher in the cerebellum than cerebral cortex and spinal cord, Cx-36 higher in the spinal cord than cerebellum, and Cx-43 higher in the cerebellum and spinal cord than cerebral cortex during basal conditions. In conclusion, maternal glucocorticoid therapy increases specific Cx, responses to different maternal courses vary among Cx and brain regions, and Cx expression differs among brain regions under basal conditions. Maternal treatment with glucocorticoids differentially modulates Cx in the fetal brain.

Current status of hypothermia for hypoxemic ischemia of the newborn

This article reviews the pathophysiology of hypoxic-ischemic brain injury, and the impact of hypothermia as neuroprotection in the clinical setting. The results of trials performed in well resourced and mid and low resourced countries is presented. Infant and childhood outcome following hypothermia is provided. Biomarkers of outcome that are clinical, electrophysiological and imaging which will be helpful to clinicians are noted. Management of infants with encephalopathy, including safety of hypothermia is reviewed. The article concludes with knowledge gaps in neuroprotection and the future of hypothermia therapy.

Status epilepticus after prolonged umbilical cord occlusion is associated with greater neural injury in [corrected] fetal sheep at term-equivalent

The majority of pre-clinical studies of hypoxic-ischemic encephalopathy at term-equivalent have focused on either relatively mild insults, or on functional paradigms of cerebral ischemia or hypoxia-ischemia/hypotension. There is surprisingly little information on the responses to single, severe ‘physiological’ insults. In this study we examined the evolution and pattern of neural injury after prolonged umbilical cord occlusion (UCO). 36 chronically instrumented fetal sheep at 125–129 days gestational age (term = 147 days) were subjected to either UCO until mean arterial pressure was < = 8 mmHg (n = 29), or sham occlusion (n = 7). Surviving fetuses were killed after 72 hours for histopathologic assessment with acid-fuchsin thionine. After UCO, 11 fetuses died with intractable hypotension and 5 ewes entered labor and were euthanized. The remaining 13 fetuses showed marked EEG suppression followed by evolving seizures starting at 5.8 (6.8) hours (median (interquartile range)). 6 of 13 developed status epilepticus, which was associated with a transient secondary increase in cortical impedance (a measure of cytotoxic edema, p<0.05). All fetuses showed moderate to severe neuronal loss in the hippocampus and the basal ganglia but mild cortical cell loss (p<0.05 vs sham occlusion). Status epilepticus was associated with more severe terminal hypotension (p<0.05) and subsequently, greater neuronal loss (p<0.05). In conclusion, profound UCO in term-equivalent fetal sheep was associated with delayed seizures, secondary cytotoxic edema, and subcortical injury, consistent with the predominant pattern after peripartum sentinel events at term. It is unclear whether status epilepticus exacerbated cortical injury or was simply a reflection of a longer duration of asphyxia.

Validation of a neuropathology score using quantitative methods to evaluate brain injury in a pig model of hypoxia ischaemia

BACKGROUND

Neuropathological examination is the classic outcome measure in experimental studies of newborn brain injury to evaluate novel therapies. We have used a graded neuropathology score in an established global model of perinatal hypoxic-ischaemic (HI) injury. We wished to validate the score using cell counting in our model.

NEW METHOD

32 newborn pigs underwent a 45 min global HI insult then maintained at normothermia (NT, rectal temperature, Trectal 38.5 °C) for 72 h or mild total body hypothermia (HT, Trectal 37.0 °C) combined with selective head cooling for 48 h and subsequently maintained at NT for 24h before brain perfusion fixation. A perinatal pathologist scored haematoxylin and eosin stained 6 μm histological sections for injury in the hippocampus and basal ganglia on a 9-step scale (0.0=no injury, 4.0=>75% injury). We counted the number of healthy neurons in the hippocampus CA1 region and putamen using morphological criteria in eight random, non-overlapping fields from representative sections.

RESULTS

Healthy neuronal cell density correlated with neuropathology score in the hippocampus CA1 (r = -0.74) and in the putamen (r = -0.75) and both measures detected a difference between groups. The correlation coefficients were better for the NT compared to the HT group in both the hippocampus (r = -0.87 vs. -0.53) and putamen (r = -0.77 vs. -0.54).

COMPARISON WITH EXISTING METHOD

We have validated a histological neuropathological scoring system in our model of perinatal HI by showing correlation between neuronal cell count and estimated injury.

CONCLUSIONS

Our neuropathology score is a valid method to assess brain injury with good reproducibility and sensitivity.

Asphyxia and therapeutic hypothermia modulate plasma nitrite concentrations and carotid vascular resistance in preterm fetal sheep

In this study, we tested the hypothesis that cerebral hypoperfusion after asphyxia and induced hypothermia is associated with reduced circulating nitrite levels as an index of nitric oxide synthase (NOS) activity. The preterm fetal sheep at 0.7 gestation (103-104 days, term = 147 days) received 25-minute umbilical cord occlusion, followed by mild whole-body cooling from 30 minutes to 72 hours after occlusion. Occlusion and induced hypothermia were independently associated with reduced carotid vascular conductance (CaVC) from 2 to 72 hours, and with transiently suppressed plasma nitrite levels at 6 hours. There was a significant within-subjects correlation (r(2) = 0.33, P = .002) between CaVC and plasma nitrite values in the first 24 hours after occlusion but not after sham occlusion. These findings suggest that in preterm fetal sheep, changes in NOS activity are an important mediator of changes in carotid vascular tone in the early recovery phase after asphyxia and may help mediate some of the vascular effects of induced hypothermia.

Selective cerebral hypothermia induced via hypothermic retrograde jugular vein saline flush in a porcine model

OBJECTIVES

Multiple methods of selective brain cooling have been used to prevent cerebral ischemia secondary to trauma and pathological or iatrogenic cerebral blood flow restriction. In this study, we tested the efficacy of hypothermic retrograde jugular vein flush (HRJVF) in eliciting selective brain hypothermia in a porcine model.

METHODS

Twelve swine were divided into two groups: retrograde jugular vein infusion (RJVI) with cold saline (4°C RJVI, n  =  6) and with room temperature saline (24°C RJVI, n  =  6). For 90 minutes, the following parameters were measured: brain parenchymal temperature, rectal temperature, intracranial pressure (ICP), mean arterial pressure, and heart rate (HR).

RESULTS

Swine receiving 4°C RJVI experienced a drop in mean brain parenchymal temperature of 1·1 ± 0·1°C, compared to 0·1 ± 0·1°C in swine receiving 24°C RJVI. At 90 minutes, mean brain parenchymal temperature in the 4°C RJVI treatment group was 35·5 ± 0·2°C, as compared to 37·1 ± 0·2°C in the 24°C RJVI treatment group (P < 0·001). In the 4°C RJVI group, the brain-systemic temperature gradient peaked 10 minutes after initiation of cooling and remained significantly different when comparing the two experimental groups (P < 0·001) throughout the duration of the 90 minutes experiment. Of note, ICP, mean arterial pressure, and HR remained constant without any significant changes or differences between treatment groups.

DISCUSSION

These results suggest that HRJVF is an effective method for selective brain hypothermia in a large animal model. Clinical application may prove effective in delaying neural ischemia.

Mechanisms of hypothermic neuroprotection

Prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death can reduce acute brain injury and improve long-term behavioral recovery in term infants and in adults after cardiac arrest. The specific mechanisms of hypothermic neuroprotection remain unclear, in part because hypothermia suppresses a broad range of potential injurious factors. This article examines proposed mechanisms in relation to the known window of opportunity for effective protection with hypothermia. Knowledge of the mechanisms of hypothermia will help guide the rational development of future combination treatments to augment neuroprotection with hypothermia and identify those most likely to benefit.

The mechanisms and treatment of asphyxial encephalopathy

Acute post-asphyxial encephalopathy occurring around the time of birth remains a major cause of death and disability. The recent seminal insight that allows active neuroprotective treatment is that even after profound asphyxia (the “primary” phase), many brain cells show initial recovery from the insult during a short “latent” phase, typically lasting approximately 6 h, only to die hours to days later after a “secondary” deterioration characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Although many of these secondary processes are potentially injurious, they appear to be primarily epiphenomena of the “execution” phase of cell death. Animal and human studies designed around this conceptual framework have shown that moderate cerebral hypothermia initiated as early as possible but before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, has been associated with potent, long-lasting neuroprotection. Recent clinical trials show that while therapeutic hypothermia significantly reduces morbidity and mortality, many babies still die or survive with disabilities. The challenge for the future is to find ways of improving the effectiveness of treatment. In this review, we will dissect the known mechanisms of hypoxic-ischemic brain injury in relation to the known effects of hypothermic neuroprotection.

Hypothermia for hypoxic-ischemic encephalopathy

Moderate to severe hypoxic-ischemic injury in newborn infants, manifested as encephalopathy immediately or within hours after birth, is associated with a high risk of either death or a lifetime with disability. In recent multicenter clinical trials, hypothermia initiated within the first 6 postnatal hours has emerged as a therapy that reduces the risk of death or impairment among infants with hypoxic-ischemic encephalopathy. Prior to hypothermia, no therapies directly targeting neonatal encephalopathy secondary to hypoxic-ischemic injury had convincing evidence of efficacy. Hypothermia therapy is now becoming increasingly available at tertiary centers. Despite the deserved enthusiasm for hypothermia, obstetric and neonatology caregivers, as well as society at large, must be reminded that in the clinical trials more than 40% of cooled infants died or survived with impairment. Although hypothermia is an evidence-based therapy, additional discoveries are needed to further improve outcome after HIE. In this article, we briefly present the epidemiology of neonatal encephalopathy due to hypoxic-ischemic injury, describe the rationale for the use of hypothermia therapy for hypoxic-ischemic encephalopathy, and present results of the clinical trials that have demonstrated the efficacy of hypothermia. We also present findings noted during and after these trials that will guide care and direct research for this devastating problem.

Strategies to prevent reperfusion injury to the brain following intrapartum hypoxia-ischemia

Hypoxia-ischemia is an infrequent event which may occur prior to or during delivery, following a period of decreased placental and/or fetal blood flow. Following recovery, a reperfusion phase and secondary energy failure may occur 6-48 h subsequent to the initial insult. Therapeutic hypothermia may be offered to infants at risk for evolving encephalopathy if identified within the 6 h therapeutic window, and should be instituted as early as possible for eligible infants. Additionally, the clinician must pay close attention to supportive measures such as avoidance of hyperthermia, as well as comprehensive management of clinical or electrographic seizures, blood pressure, blood glucoses, and carbon dioxide levels.

Therapeutic hypothermia in neonatal hypoxic ischemic encephalopathy: electrographic seizures and magnetic resonance imaging evidence of injury

OBJECTIVE

To evaluate the electrographic seizure burden in neonates with hypoxic ischemic encephalopathy (HIE) treated with or without therapeutic hypothermia and stratified results by severity of HIE and severity of injury as assessed by magnetic resonance imaging (MRI).

STUDY DESIGN

Between 2007 and 2011, video-electroencephalography (EEG) monitoring was initiated in neonates with moderate to severe HIE. Seizure burden (in seconds) was calculated, and brain MRI scans were quantitatively scored. Data were analyzed by ANOVA, the Student t test, and the χ(2) test.

RESULTS

Sixty-nine neonates with moderate or severe HIE were prospectively enrolled, including 51 who received therapeutic hypothermia and 18 who did not. The mean duration of video-EEG monitoring was longer in the therapeutic hypothermia group (72 ± 34 hours vs 48 ± 34 hours; P = .01). The therapeutic hypothermia group had a lower electrographic seizure burden (log units) after controlling for injury, as assessed by MRI (2.9 ± 0.6 vs 6.2 ± 0.9; P = .003). A reduction in seizure burden was seen in neonates with moderate HIE (P = .0001), but not in those with severe HIE (P = .80). Among neonates with injury assessed by MRI, seizure burden was lower in those with mild (P = .0004) and moderate (P = .02) injury, but not in those with severe injury (P = .90).

CONCLUSION

Therapeutic hypothermia was associated with reduced electrographic seizure burden in neonatal HIE. This effect was detected on video-EEG in infants with moderate HIE, but not in those with severe HIE. When stratified by injury as assessed by MRI, therapeutic hypothermia was associated with a reduced seizure burden in infants with mild and moderate injury, but not in those with severe injury.

Pathophysiology of an hypoxic–ischemic insult during the perinatal period

Hypoxia-ischemia is a leading cause of morbidity and mortality in the perinatal period with an incidence of 1/4000 live births. Biochemical events such as energy failure, membrane depolarization, brain edema, an increase of neurotransmitter release and inhibition of uptake, an increase of intracellular Ca(2+), production of oxygen-free radicals, lipid peroxidation, and a decrease of blood flow are triggered by hypoxia-ischemia and may lead to brain dysfunction and neuronal death. These abnormalities can result in mental impairments, seizures, and permanent motor deficits, such as cerebral palsy. The physical and emotional strain that is placed on the children affected and their families is enormous. The care that these individuals need is not only confined to childhood, but rather extends throughout their entire life span, so it is very important to understand the pathophysiology that follows a hypoxic-ischemic insult. This review will highlight many of the mechanisms that lead to neuronal death and include the emerging area of white matter injury as well as the role of inflammation and will provide a summary of therapeutic strategies. Hypothermia and oxygen will also be discussed as treatments that currently lack a specific target in the hypoxic/ischemic cascade.

Connexin hemichannel blockade is neuroprotective after, but not during, global cerebral ischemia in near-term fetal sheep

There is increasing evidence that connexin hemichannels, the half gap junctions that sit unopposed in the cell membrane, can open during ischemia and that blockade of connexin43 hemichannels after cerebral ischemia can improve neural outcomes. However, it is unclear whether connexin blockade during ischemia is protective. In the present study global cerebral ischemia was induced by 30 min of bilateral carotid artery occlusion in near-term (128 ± 1 day gestation age) fetal sheep. A specific mimetic peptide that blocks connexin43 hemichannels was infused into the lateral ventricle for either 1h before and during ischemia (intra-ischemia group, n=6) or for 25 h starting 90 min after the end of ischemia (post-ischemia group, n=7). The vehicle was infused in the ischemia-vehicle group (n=6) and sham-controls received sham occlusion plus vehicle (n=10). The post-ischemia group showed enhanced recovery of EEG power from day five until the end of the experiment (-5 ± 1.6 dB) compared to ischemia-vehicle (-13 ± 1.9 dB, p<0.05) and intra-ischemia infusion (-14.4 ± 3.6 dB, p<0.05). Post-ischemic infusion was associated with higher neuronal counts compared to ischemia-vehicle and intra-ischemia in the cortex (p<0.05) but not the CA1 and CA3 regions of the hippocampus. Oligodendrocyte cell counts in the intragyral and periventricular white matter were significantly higher in the post-ischemia group compared to ischemia-vehicle and intra-ischemia infusion (p<0.05). These large animal data support the hypothesis that connexin hemichannel opening after, but not during, ischemia contributes to the spread of white and gray matter injury of the developing brain.