Modest hypothermia provides partial neuroprotection when used for immediate resuscitation after brain ischemia

Therapeutic hypothermia success for hypoxic-ischaemic encephalopathy in Latin America: Eight-year experience in EpicLatino Neonatal Network

AIM

A study reported that therapeutic hypothermia (TH) did not reduce the combined prognosis of mortality and disability at 18 months, in low- and middle-income countries for patients with hypoxic ischaemic encephalopathy (HIE) who received TH, suggesting its no implementation in these regions. We described characteristics, mortality, and neurological response before and after the use of TH in newborns with HIE within the EpicLatino Neonatal Network (ENN) and described the population of infants with HIE treated and not treated with TH.

METHODS

Data were collected from 2015 to 2022 for patients with HIE. Mortality rates and Sarnat scores were compared before and after TH. The Wilcoxon Signed-Rank Test was used for comparisons.

RESULTS

In this observational study 518 neonates of our total population of 26 970, had HIE (1.92%) of whom 150 underwent TH. Ten out of 21 neonatal intensive care units (NICUs) provided TH. The Wilcoxon Signed Rank Test for 138 cases with complete data showed a significant difference.

CONCLUSION

The findings support the benefits of TH in HIE within this cohort. TH should not be withheld solely due to the economic status of the country. A strict patient selection and TH protocol are essential.

Early assessment of injury with optical markers in a piglet model of neonatal encephalopathy

BACKGROUND

Opportunities for adjunct therapies with cooling in neonatal encephalopathy are imminent; however, robust biomarkers of early assessment are lacking. Using an optical platform of broadband near-infrared spectroscopy and diffuse correlation spectroscopy to directly measure mitochondrial metabolism (oxCCO), oxygenation (HbD), cerebral blood flow (CBF), we hypothesised optical indices early (1-h post insult) after hypoxia-ischaemia (HI) predicts insult severity and outcome.

METHODS

Nineteen newborn large white piglets underwent continuous neuromonitoring as controls or following moderate or severe HI. Optical indices were expressed as mean semblance (phase difference) and coherence (spectral similarity) between signals using wavelet analysis. Outcome markers included the lactate/N-acetyl aspartate (Lac/NAA) ratio at 6 h on proton MRS and TUNEL cell count.

RESULTS

CBF-HbD semblance (cerebrovascular dysfunction) correlated with BGT and white matter (WM) Lac/NAA (r2 = 0.46, p = 0.004, r2 = 0.45, p = 0.004, respectively), TUNEL cell count (r2 = 0.34, p = 0.02) and predicted both initial insult (r2 = 0.62, p = 0.002) and outcome group (r2 = 0.65 p = 0.003). oxCCO-HbD semblance (cerebral metabolic dysfunction) correlated with BGT and WM Lac/NAA (r2 = 0.34, p = 0.01 and r2 = 0.46, p = 0.002, respectively) and differentiated between outcome groups (r2 = 0.43, p = 0.01).

CONCLUSION

Optical markers of both cerebral metabolic and vascular dysfunction 1 h after HI predicted injury severity and subsequent outcome in a pre-clinical model.

IMPACT

This study highlights the possibility of using non-invasive optical biomarkers for early assessment of injury severity following neonatal encephalopathy, relating to the outcome. Continuous cot-side monitoring of these optical markers can be useful for disease stratification in the clinical population and for identifying infants who might benefit from future adjunct neuroprotective therapies beyond cooling.

Hypothermic Protection in Neocortex Is Topographic and Laminar, Seizure Unmitigating, and Partially Rescues Neurons Depleted of RNA Splicing Protein Rbfox3/NeuN in Neonatal Hypoxic-Ischemic Male Piglets

The effects of hypothermia on neonatal encephalopathy may vary topographically and cytopathologically in the neocortex with manifestations potentially influenced by seizures that alter the severity, distribution, and type of neuropathology. We developed a neonatal piglet survival model of hypoxic-ischemic (HI) encephalopathy and hypothermia (HT) with continuous electroencephalography (cEEG) for seizures. Neonatal male piglets received HI-normothermia (NT), HI-HT, sham-NT, or sham-HT treatments. Randomized unmedicated sham and HI piglets underwent cEEG during recovery. Survival was 2-7 days. Normal and pathological neurons were counted in different neocortical areas, identified by cytoarchitecture and connectomics, using hematoxylin and eosin staining and immunohistochemistry for RNA-binding FOX-1 homolog 3 (Rbfox3/NeuN). Seizure burden was determined. HI-NT piglets had a reduced normal/total neuron ratio and increased ischemic-necrotic/total neuron ratio relative to sham-NT and sham-HT piglets with differing severities in the anterior and posterior motor, somatosensory, and frontal cortices. Neocortical neuropathology was attenuated by HT. HT protection was prominent in layer III of the inferior parietal cortex. Rbfox3 immunoreactivity distinguished cortical neurons as: Rbfox3-positive/normal, Rbfox3-positive/ischemic-necrotic, and Rbfox3-depleted. HI piglets had an increased Rbfox3-depleted/total neuron ratio in layers II and III compared to sham-NT piglets. Neuronal Rbfox3 depletion was partly rescued by HT. Seizure burdens in HI-NT and HI-HT piglets were similar. We conclude that the neonatal HI piglet neocortex has: (1) suprasylvian vulnerability to HI and seizures; (2) a limited neuronal cytopathological repertoire in functionally different regions that engages protective mechanisms with HT; (3) higher seizure burden, insensitive to HT, that is correlated with more panlaminar ischemic-necrotic neurons in the somatosensory cortex; and (4) pathological RNA splicing protein nuclear depletion that is sensitive to HT. This work demonstrates that HT protection of the neocortex in neonatal HI is topographic and laminar, seizure unmitigating, and restores neuronal depletion of RNA splicing factor.

Oleuropein Activates Neonatal Neocortical Proteasomes, but Proteasome Gene Targeting by AAV9 Is Variable in a Clinically Relevant Piglet Model of Brain Hypoxia-Ischemia and Hypothermia

Cerebral hypoxia-ischemia (HI) compromises the proteasome in a clinically relevant neonatal piglet model. Protecting and activating proteasomes could be an adjunct therapy to hypothermia. We investigated whether chymotrypsin-like proteasome activity differs regionally and developmentally in the neonatal brain. We also tested whether neonatal brain proteasomes can be modulated by oleuropein, an experimental pleiotropic neuroprotective drug, or by targeting a proteasome subunit gene using recombinant adeno-associated virus-9 (AAV). During post-HI hypothermia, we treated piglets with oleuropein, used AAV-short hairpin RNA (shRNA) to knock down proteasome activator 28γ (PA28γ), or enforced PA28γ using AAV-PA28γ with green fluorescent protein (GFP). Neonatal neocortex and subcortical white matter had greater proteasome activity than did liver and kidney. Neonatal white matter had higher proteasome activity than did juvenile white matter. Lower arterial pH 1 h after HI correlated with greater subsequent cortical proteasome activity. With increasing brain homogenate protein input into the assay, the initial proteasome activity increased only among shams, whereas HI increased total kinetic proteasome activity. OLE increased the initial neocortical proteasome activity after hypothermia. AAV drove GFP expression, and white matter PA28γ levels correlated with proteasome activity and subunit levels. However, AAV proteasome modulation varied. Thus, neonatal neocortical proteasomes can be pharmacologically activated. HI slows the initial proteasome performance, but then augments ongoing catalytic activity. AAV-mediated genetic manipulation in the piglet brain holds promise, though proteasome gene targeting requires further development.

Role of Optical Neuromonitoring in Neonatal Encephalopathy-Current State and Recent Advances

Neonatal encephalopathy (NE) in term and near-term infants is a significant global health problem; the worldwide burden of disease remains high despite the introduction of therapeutic hypothermia. Assessment of injury severity and effective management in the neonatal intensive care unit (NICU) relies on multiple monitoring modalities from systemic to brain-specific. Current neuromonitoring tools provide information utilized for seizure management, injury stratification, and prognostication, whilst systemic monitoring ensures multi-organ dysfunction is recognized early and supported wherever needed. The neuromonitoring technologies currently used in NE however, have limitations in either their availability during the active treatment window or their reliability to prognosticate and stratify injury confidently in the early period following insult. There is therefore a real need for a neuromonitoring tool that provides cot side, early and continuous monitoring of brain health which can reliably stratify injury severity, monitor response to current and emerging treatments, and prognosticate outcome. The clinical use of near-infrared spectroscopy (NIRS) technology has increased in recent years. Research studies within this population have also increased, alongside the development of both instrumentation and signal processing techniques. Increasing use of commercially available cerebral oximeters in the NICU, and the introduction of advanced optical measurements using broadband NIRS (BNIRS), frequency domain NIRS (FDNIRS), and diffuse correlation spectroscopy (DCS) have widened the scope by allowing the direct monitoring of oxygen metabolism and cerebral blood flow, both key to understanding pathophysiological changes and predicting outcome in NE. This review discusses the role of optical neuromonitoring in NE and why this modality may provide the next significant piece of the puzzle toward understanding the real time state of the injured newborn brain.

Neuroprotection Strategies for Term Encephalopathy

Brain injury in the full-term and near-term neonates is a significant cause of mortality and long-term morbidity, resulting in injury patterns distinct from that seen in premature infants and older patients. Therapeutic hypothermia improves long-term outcomes for many of these infants, but there is a continued search for therapies to enhance the plasticity of the newborn brain, resulting in long-term repair. It is likely that a combination strategy utilizing both early and late interventions may have the most benefit, capitalizing on endogenous mechanisms triggered by hypoxia or ischemia. Optimizing care of these critically ill newborns in the acute setting is also vital for improving both short- and long-term outcomes.

An experimental study and finite element modeling of head and neck cooling for brain hypothermia

Reducing brain temperature by head and neck cooling is likely to be the protective treatment for humans when subjects to sudden cardiac arrest. This study develops the experimental validation model and finite element modeling (FEM) to study the head and neck cooling separately, which can induce therapeutic hypothermia focused on the brain. Anatomically accurate geometries based on CT images of the skull and carotid artery are utilized to find the 3D geometry for FEM to analyze the temperature distributions and 3D-printing to build the physical model for experiment. The results show that FEM predicted and experimentally measured temperatures have good agreement, which can be used to predict the temporal and spatial temperature distributions of the tissue and blood during the head and neck cooling process. Effects of boundary condition, perfusion, blood flow rate, and size of cooling area are studied. For head cooling, the cooling penetration depth is greatly depending on the blood perfusion in the brain. In the normal blood flow condition, the neck internal carotid artery temperature is decreased only by about 0.13°C after 60min of hypothermia. In an ischemic (low blood flow rate) condition, such temperature can be decreased by about 1.0°C. In conclusion, decreasing the blood perfusion and metabolic reduction factor could be more beneficial to cool the core zone. The results also suggest that more SBC researches should be explored, such as the optimization of simulation and experimental models, and to perform the experiment on human subjects.

Therapeutic hypothermia translates from ancient history in to practice

Acute postasphyxial encephalopathy around the time of birth remains a major cause of death and disability. The possibility that hypothermia may be able to prevent or lessen asphyxial brain injury is a "dream revisited". In this review, a historical perspective is provided from the first reported use of therapeutic hypothermia for brain injuries in antiquity, to the present day. The first uncontrolled trials of cooling for resuscitation were reported more than 50 y ago. The seminal insight that led to the modern revival of studies of neuroprotection was that after profound asphyxia, many brain cells show initial recovery from the insult during a short "latent" phase, typically lasting ~6 h, only to die hours to days later during a "secondary" deterioration phase characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Studies designed around this conceptual framework showed that mild hypothermia initiated as early as possible before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, is associated with potent, long-lasting neuroprotection. There is now compelling evidence from randomized controlled trials that mild induced hypothermia significantly improves intact survival and neurodevelopmental outcomes to midchildhood.

Effects of hypothermia on skeletal ischemia reperfusion injury in rats

OBJECTIVE

The aim of this study was to investigate the effect of hypothermia (H) on skeletal ischemia-reperfusion (IR) injury in rats by measuring malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), nitric oxide (NO), and interleukin-1 beta (IL-1β) in muscle, and measureing immunohistochemical-inducible nitric oxide synthase (iNOS) staining of skeletal muscle.

MATERIALS AND METHODS

Eighteen Wistar Albino rats were divided randomly into three groups (sham, IR, hypothermia) (n=6). The sham group had all procedures without the IR period. The lower right extremity of rats in the IR and hypothermia groups was subjected to 2 hours of ischemia and 22 hours of reperfusion by applying a clamp on the common iliac artery and a rubber-band at the level of the lesser trochanter under general anesthesia. Rats in the hypothermia group underwent 4 hours of hypothermia during the first four hours of reperfusion in addition to a 2-hour ischemia and 22-hour reperfusion period. All rats were sacrificed at end of the IR period using a high dose of anesthesia. The tibialis anterior muscles were preserved. Immunohistochemical iNOS staining was performed, and MDA, SOD, GSH-Px, NO, and IL-1β were measured in the muscle.

RESULTS

The level of MDA, NO, and IL-1β in muscle was increased in the IR group compared with that in the sham group, but these parameters were decreased in the hypothermia group compared with the IR group. The activities of SOD and GSH-Px in muscle were decreased in the IR group; however, these parameters were increased in the hypothermia group. The score and intensity of iNOS staining of skeletal muscle was dens in IR group, mild in hypothermia group, and weak in sham group.

CONCLUSION

The present study has shown that hypothermia reduced IR injury in the skeletal muscle by decreasing the levels of MDA, NO, and IL-1β, and increasing the activities of SOD and GSH-Px. In addition, hypothermia attenuated the score and intensity of iNOS staining.

Rationale, timeline, study design, and protocol overview of the therapeutic hypothermia after pediatric cardiac arrest trials

OBJECTIVE

To describe the rationale, timeline, study design, and protocol overview of the Therapeutic Hypothermia after Pediatric Cardiac Arrest trials.

DESIGN

Multicenter randomized controlled trials.

SETTING

Pediatric intensive care and cardiac ICUs in the United States and Canada.

PATIENTS

Children from 48 hours to 18 years old, who have return of circulation after cardiac arrest, who meet trial eligibility criteria, and whose guardians provide written consent.

INTERVENTIONS

Therapeutic hypothermia or therapeutic normothermia.

MEASUREMENTS AND MAIN RESULTS

From concept inception in 2002 until trial initiation in 2009, 7 years were required to plan and operationalize the Therapeutic Hypothermia after Pediatric Cardiac Arrest trials. Two National Institute of Child Health and Human Development clinical trial planning grants (R21 and R34) supported feasibility assessment and protocol development. Two clinical research networks, Pediatric Emergency Care Applied Research Network and Collaborative Pediatric Critical Care Research Network, provided infrastructure resources. Two National Heart Lung Blood Institute U01 awards provided funding to conduct separate trials of in-hospital and out-of-hospital cardiac arrest. A pilot vanguard phase that included half the clinical sites began on March 9, 2009, and this was followed by full trial funding through 2015.

CONCLUSIONS

Over a decade will have been required to plan, design, operationalize, and conduct the Therapeutic Hypothermia after Pediatric Cardiac Arrest trials. Details described in this report, such as participation of clinical research networks and clinical trial planning grants utilization, may be of utility for individuals who are planning investigator-initiated, federally supported clinical trials.

Cooling for newborns with hypoxic ischaemic encephalopathy

BACKGROUND

Newborn animal studies and pilot studies in humans suggest that mild hypothermia following peripartum hypoxia-ischaemia in newborn infants may reduce neurological sequelae without adverse effects.

OBJECTIVES

To determine the effect of therapeutic hypothermia in encephalopathic asphyxiated newborn infants on mortality, long-term neurodevelopmental disability and clinically important side effects.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review Group as outlined in The Cochrane Library (Issue 2, 2007). Randomised controlled trials evaluating therapeutic hypothermia in term and late preterm newborns with hypoxic ischaemic encephalopathy were identified by searching the Oxford Database of Perinatal Trials, the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, 2007, Issue 2), MEDLINE (1966 to June 2007), previous reviews including cross-references, abstracts, conferences, symposia proceedings, expert informants and journal handsearching. We updated this search in May 2012.

SELECTION CRITERIA

We included randomised controlled trials comparing the use of therapeutic hypothermia with standard care in encephalopathic term or late preterm infants with evidence of peripartum asphyxia and without recognisable major congenital anomalies. The primary outcome measure was death or long-term major neurodevelopmental disability. Other outcomes included adverse effects of cooling and 'early' indicators of neurodevelopmental outcome.

DATA COLLECTION AND ANALYSIS

Four review authors independently selected, assessed the quality of and extracted data from the included studies. Study authors were contacted for further information. Meta-analyses were performed using risk ratios (RR) and risk differences (RD) for dichotomous data, and weighted mean difference for continuous data with 95% confidence intervals (CI).

MAIN RESULTS

We included 11 randomised controlled trials in this updated review, comprising 1505 term and late preterm infants with moderate/severe encephalopathy and evidence of intrapartum asphyxia. Therapeutic hypothermia resulted in a statistically significant and clinically important reduction in the combined outcome of mortality or major neurodevelopmental disability to 18 months of age (typical RR 0.75 (95% CI 0.68 to 0.83); typical RD -0.15, 95% CI -0.20 to -0.10); number needed to treat for an additional beneficial outcome (NNTB) 7 (95% CI 5 to 10) (8 studies, 1344 infants). Cooling also resulted in statistically significant reductions in mortality (typical RR 0.75 (95% CI 0.64 to 0.88), typical RD -0.09 (95% CI -0.13 to -0.04); NNTB 11 (95% CI 8 to 25) (11 studies, 1468 infants) and in neurodevelopmental disability in survivors (typical RR 0.77 (95% CI 0.63 to 0.94), typical RD -0.13 (95% CI -0.19 to -0.07); NNTB 8 (95% CI 5 to 14) (8 studies, 917 infants). Some adverse effects of hypothermia included an increase sinus bradycardia and a significant increase in thrombocytopenia.

AUTHORS' CONCLUSIONS

There is evidence from the 11 randomised controlled trials included in this systematic review (N = 1505 infants) that therapeutic hypothermia is beneficial in term and late preterm newborns with hypoxic ischaemic encephalopathy. Cooling reduces mortality without increasing major disability in survivors. The benefits of cooling on survival and neurodevelopment outweigh the short-term adverse effects. Hypothermia should be instituted in term and late preterm infants with moderate-to-severe hypoxic ischaemic encephalopathy if identified before six hours of age. Further trials to determine the appropriate techniques of cooling, including refinement of patient selection, duration of cooling and method of providing therapeutic hypothermia, will refine our understanding of this intervention.

Hypoxic-ischemic encephalopathy and novel strategies for neuroprotection

This article covers the outcome of full-term infants with encephalopathy due to hypoxic-ischemia and pathophysiology of brain injury following hypoxic-ischemia. Clinical and imaging evidence for hypothermia for neuroprotection is presented. The outcome of infants with hypothermia for encephalopathy due to hypoxic-ischemia from recent trials is summarized. Facts regarding the clinical application of cooling obtained from the randomized trials and knowledge gaps in hypothermic therapy are presented. The review concludes with the future of hypothermia for neuroprotection.

BRAIN TEMPERATURE CALCULATIONS FOR SWINE USING EXPERIMENTAL MEASUREMENTS OF CEREBRAL BLOOD FLOW

In this study, numerical simulations are performed to analyze the brain temperature reduction in swine during selective head cooling, whole body cooling or while the animals experience ischemia. Brain temperature is calculated using a time dependent thermal model that incorporates available experimental measurements of the rectal temperature, the cerebral blood flow and the cerebral metabolic rate of oxygen consumption.

The calculated temperature distribution is validated against the in vivo temperature measurements recorded during the different experiments. These comparisons help to better understand the relations between brain temperature, blood flow and metabolic activity, which are essential to successfully apply hypothermia in the treatment of brain injury.

The calculations presented here reproduce the temperature behavior observed in all the experiments considered. It is observed that the arterial temperature and the cerebral metabolic rate are important parameters that affect the deep tissue temperature. It is also concluded that the accurate knowledge of parameters such as the skin and bone thermal conductivity are necessary for effective modeling.

Brain energy metabolism during experimental neonatal seizures

During flurothyl seizures in 4-day-old rats, cortical concentration of ATP, phosphocreatine and glucose fell while lactate rose. Cortical energy use rate more than doubled, while glycolytic rate increased fivefold. Calculation of the cerebral metabolic balance during sustained seizures suggests that energy balance could be maintained in hyperglycemic animals, and would decline slowly in normoglycemia, but would be compromised by concurrent hypoglycemia, hyperthermia or hypoxia. These results suggest that the metabolic challenge imposed on the brain by this model of experimental neonatal seizures is milder than that seen at older ages, but can become critical when associated with other types of metabolic stress.

Therapeutic hypothermia for newborn infants with hypoxic-ischaemic encephalopathy

Peripartum asphyxia complicated by moderate or severe hypoxic-ischaemic encephalopathy is a devastating global health issue. A therapeutic 'window of opportunity' exists after resuscitation of the asphyxiated newborn and before the delayed phase of neuronal loss. Animal studies demonstrated that neuronal injury following hypoxia-ischaemia can be prevented or reduced by a mild reduction in brain temperature. Human infant pilot studies confirmed feasibility, without major adverse effects. Randomised trials and systematic reviews comprising term infants with moderate or severe encephalopathy and peripartum asphyxia have established the neuroprotective benefit of therapeutic hypothermia. Hypothermia reduces mortality or major disability to 18 months of age, as well as cerebral palsy, and neuromotor and cognitive delay. Importantly, mortality is reduced without any increase in major neurodevelopmental disability in survivors, and with only minor adverse effects. The evidence supports therapeutic hypothermia when used within strict protocols in tertiary centres to improve the outcome for term and near-term newborns with moderate or severe hypoxic-ischaemic encephalopathy. Equally strict protocols in non-tertiary nurseries will enable earlier initiation of hypothermia under guidance of the regional neonatal intensive care unit and transport team.

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.

A comparison of cooling methods used in therapeutic hypothermia for perinatal asphyxia

OBJECTIVE

The objective of this study was to compare cooling methods during therapeutic hypothermia (TH) for moderate or severe perinatal asphyxia with regard to temperature and hemodynamic stability.

METHODS

A total of 73 newborns received TH in our center between 1999 and 2009 by 4 methods: (1) selective head cooling with mild systemic hypothermia by using cap (SHC; n = 20); (2) whole-body cooling with mattress manually controlled (WBCmc; n = 23); (3) whole-body cooling with body wrap servo-controlled (WBCsc; n = 28); and (4) whole-body cooling with water-filled gloves (n = 2). Target rectal temperatures (Trec) were 34.5 +/- 0.5 degrees C (SHC) and 33.5 +/- 0.5 degrees C (WBC). Trec, mean arterial blood pressure, and heart rate were collected from retrospective chart review.

RESULTS

Groups had similar baseline characteristics and condition at birth. Trec was within target temperature +/-0.5 degree C for 97% of the time in infants with WBCsc, 81% in infants with WBCmc, 76% in infants with SHC, and 74% in infants who were cooled with gloves. Mean overshoot was 0.3 degree C for WBCsc, 1.3 degrees C for WBCmc, and 0.8 degree C for SHC groups. There was no difference in mean arterial blood pressure or mean heart between groups during the maintenance of cooling. In infants who were rewarmed at similar speed, there was greater variation in Trec in the SHC compared with the WBCsc group.

CONCLUSIONS

Manually controlled cooling systems are associated with greater variability in Trec compared with servo-controlled systems. A manual mattress often causes initial overcooling. It is unknown whether large variation in temperature adversely affects the neuroprotection of TH.

The discovery of hypothermic neural rescue therapy for perinatal hypoxic-ischemic encephalopathy

The development of the concepts of delayed post-ischaemic neuronal death and neural rescue brought about a search for clinical treatments to reduce brain damage after birth asphyxia. Cooling had long been an unproven empyrical therapy, and a 20 year programme of careful laboratory and clinical research has proved that hypothermia reduces neurological damage in infants suffering perinatal asphyxial encephalopathy.

Neuroprotection in the newborn infant

Neonatal brain injury is an important cause of death and disability, with pathways of oxidant stress, inflammation, and excitotoxicity that lead to damage that progresses over a long period of time. Therapies have classically targeted individual pathways during early phases of injury, but more recent therapies such as growth factors may also enhance cell proliferation, differentiation, and migration over time. More recent evidence suggests combined therapy may optimize repair, decreasing cell injury while increasing newly born cells.

Hypothermia for hypoxic-ischemic brain injury

Hypoxic-ischemic brain injury and hypoxic-ischemic encephalopathy (HIE) remain a serious problem for both preterm and term neonates with the spectrum of injury ranging from neuronal injury to encephalopathy and death. Neonatal encephalopathy due to such injury occurs in 3-9 of every 1000 term infants. Of these, it is estimated that nearly a third to a half will either have severe adverse outcomes or die. Treatment of infants with HIE remains generally supportive with attention to resuscitation, fluid and electrolyte homeostasis, maintenance of acid-base balance, nutrition and feeding issues and treatment of seizures.

Use of therapeutic hypothermia for term infants with hypoxic-ischemic encephalopathy

Newborn encephalopathy represents a clinical syndrome with diverse causes, many of which may result in brain injury. Hypoxic-ischemic encephalopathy represents a subset of newborns with encephalopathy and, in contrast to other causes, may have a modifiable outcome. Laboratory research has demonstrated robust neuroprotection associated with reductions of brain temperature following hypoxia-ischemia in animals. The neuroprotective effects of hypothermia reflect antagonism of multiple cascades of events that contribute to brain injury. Clinical trials have translated laboratory observations into successful interventions. Hypoxicischemic encephalopathy is often unanticipated, unavoidable, and may occur in any obstetric setting. Pediatricians and other providers based in community hospitals play a critical role in the initial assessment, recognition, and stabilization of infants who may be candidates for therapeutic hypothermia.

Delivery room management of the newborn

Neonatal resuscitation is an attempt to facilitate the dynamic transition from fetal to neonatal physiology. This article outlines the current practices in delivery room management of the neonate. Developments in cardiopulmonary resuscitation techniques for term and preterm infants and advances in the areas of cerebral resuscitation and thermoregulation are reviewed. Resuscitation in special circumstances (such as the presence of congenital anomalies) are also covered. The importance of communication with other members of the health care team and the family is discussed. Finally, future trends in neonatal resuscitation are explored.

Therapeutic hypothermia for neuroprotection

This review briefly discusses induced therapeutic hypothermia (TH), which represents the intentional induction of a lowered core body temperature of 35 degrees C or less. The focus is on resuscitative or postarrest hypothermia, the data that support it, and the practical issues pertaining to TH implementation.

Therapeutic hypothermia in neonates. Review of current clinical data, ILCOR recommendations and suggestions for implementation in neonatal intensive care units

Recent evidence suggests that the current ILCOR guidelines regarding hypothermia for the treatment of neonatal encephalopathy need urgent revision. In 2005 when the current ILCOR guidelines were finalised one large (CoolCap trial, n=235) and one small RCT (n=67), in addition to pilot trials, had been published, and demonstrated that therapeutic hypothermia after perinatal asphyxia was safe. The CoolCap trial showed a borderline overall effect on death and disability at 18 months of age, but significant improvement in a large subset of infants with less severe electroencephalographic changes. Based on this and other available evidence, the 2005 ILCOR guidelines supported post-resuscitation hypothermia in paediatric patients after cardiac arrest, but not after neonatal resuscitation. Subsequently, a whole body cooling trial supported by the NICHD reported a significant overall improvement in death or disability. Further large neonatal trials of hypothermia have stopped recruitment and their final results are likely to be published 2009-2011. Many important questions around the optimal therapeutic use of hypothermia remain to be answered. Nevertheless, independent meta-analyses of the published trials now indicate a consistent, robust beneficial effect of therapeutic hypothermia for moderate to severe neonatal encephalopathy, with a mean NNT between 6 and 8. Given that there is currently no other clinically proven treatment for infants with neonatal encephalopathy we propose that an interim advisory statement should be issued to support and guide the introduction of therapeutic hypothermia into routine clinical practice.

Therapeutics for neonatal brain injury

Neonatal brain injury is an important cause of death and neurodevelopmental delay. Multiple pathways of oxidant stress, inflammation, and excitotoxicity lead to both early and late phases of cell damage and death. Therapies targeting these different pathways have shown potential in protecting the brain from ongoing injury. More recent therapies, such as growth factors, have demonstrated an ability to increase cell proliferation and repair over longer periods of time. Even though hypothermia, which decreases cerebral metabolism and possibly affects other mechanisms, may show some benefit in particular cases, no widely effective therapeutic interventions for human neonates exist. In this review, we summarize recent findings in neuroprotection and neurogenesis for the immature brain, including combination therapy to optimize repair.

Cooling for newborns with hypoxic ischaemic encephalopathy

BACKGROUND

Newborn animal studies and pilot studies in humans suggest that mild hypothermia following peripartum hypoxia-ischaemia in newborn infants may reduce neurological sequelae without adverse effects.

OBJECTIVES

To determine the effect of therapeutic hypothermia in encephalopathic asphyxiated newborn infants on mortality, long-term neurodevelopmental disability and clinically important side effects.

SEARCH STRATEGY

The standard search strategy of the Neonatal Review Group as outlined in The Cochrane Library (Issue 2, 2007) was used. Randomised controlled trials evaluating therapeutic hypothermia in term newborns with hypoxic ischaemic encephalopathy were identified by searching the Oxford Database of Perinatal Trials, the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 2007), MEDLINE (1966 to June 2007), previous reviews including cross-references, abstracts, conferences, symposia proceedings, expert informants and journal hand searching.

SELECTION CRITERIA

Randomised controlled trials comparing the use of therapeutic hypothermia with standard care in encephalopathic newborn infants with evidence of peripartum asphyxia and without recognisable major congenital anomalies were included. The primary outcome measure was death or long-term major neurodevelopmental disability. Other outcomes included adverse effects of cooling and 'early' indicators of neurodevelopmental outcome.

DATA COLLECTION AND ANALYSIS

Three review authors independently selected, assessed the quality of and extracted data from the included studies. Authors were contacted for further information. Meta-analyses were performed using relative risk and risk difference for dichotomous data, and weighted mean difference for continuous data with 95% confidence intervals.

MAIN RESULTS

Eight randomised controlled trials were included in this review, comprising 638 term infants with moderate/ severe encephalopathy and evidence of intrapartum asphyxia. Therapeutic hypothermia resulted in a statistically significant and clinically important reduction in the combined outcome of mortality or major neurodevelopmental disability to 18 months of age [typical RR 0.76 (95% CI 0.65, 0.89), typical RD -0.15 (95% CI -0.24, -0.07), NNT 7 (95% CI 4, 14)]. Cooling also resulted in statistically significant reductions in mortality [typical RR 0.74 (95% CI 0.58, 0.94), typical RD -0.09 (95% CI -0.16, -0.02), NNT 11 (95% CI 6, 50)] and in neurodevelopmental disability in survivors [typical RR 0.68 (95% CI 0.51, 0.92), typical RD -0.13 (95% CI -0.23, -0.03), NNT 8 (95% CI 4, 33)]. Some adverse effects of hypothermia included an increase in the need for inotrope support of borderline significance and a significant increase in thrombocytopaenia.

AUTHORS' CONCLUSIONS

There is evidence from the eight randomised controlled trials included in this systematic review (n = 638) that therapeutic hypothermia is beneficial to term newborns with hypoxic ischaemic encephalopathy. Cooling reduces mortality without increasing major disability in survivors. The benefits of cooling on survival and neurodevelopment outweigh the short-term adverse effects. However, this review comprises an analysis based on less than half of all infants currently known to be randomised into eligible trials of cooling. Incorporation of data from ongoing and completed randomised trials (n = 829) will be important to clarify the effectiveness of cooling and to provide more information on the safety of therapeutic hypothermia, but could also alter these conclusions. Further trials to determine the appropriate method of providing therapeutic hypothermia, including comparison of whole body with selective head cooling with mild systemic hypothermia, are required.

Neuroprotection (including hypothermia)

There have been over 2000 publications in the last year addressing the topic of neuroprotection. Novel and emerging therapeutic targets that have been explored include cerebral inflammation, hypothermia, neural transplantation and repair and gene therapy. Unfortunately, with few exceptions, the successes of experimental neuroprotection have not been translated into clinical practice. The possible reasons for the discrepancy between experimental success and clinical benefit are explored.

Translational stroke research in the developing brain

Preclinical animal models can help guide the development of clinical pediatric and newborn stroke trials. Data obtained using currently available models of hypoxia-ischemia and focal stroke have demonstrated the need for age-appropriate models. There are age-related differences in susceptibility of the immature brain to oxidative stress and inflammation, as well as in the rate and degree of apoptotic neuronal death. These issues need to be carefully addressed in designing future clinical trials.

Hypothermic neuroprotection

The possibility that hypothermia during or after resuscitation from asphyxia at birth, or cardiac arrest in adults, might reduce evolving damage has tantalized clinicians for a very long time. It is now known that severe hypoxia-ischemia may not necessarily cause immediate cell death, but can precipitate a complex biochemical cascade leading to the delayed neuronal loss. Clinically and experimentally, the key phases of injury include a latent phase after reperfusion, with initial recovery of cerebral energy metabolism but EEG suppression, followed by a secondary phase characterized by accumulation of cytotoxins, seizures, cytotoxic edema, and failure of cerebral oxidative metabolism starting 6 to 15 h post insult. Although many of the secondary processes can be injurious, they appear to be primarily epiphenomena of the 'execution' phase of cell death. Studies designed around this conceptual framework have shown that moderate cerebral hypothermia initiated as early as possible before the onset of secondary deterioration, and continued for a sufficient duration in relation to the severity of the cerebral injury, has been associated with potent, long-lasting neuroprotection in both adult and perinatal species. Two large controlled trials, one of head cooling with mild hypothermia, and one of moderate whole body cooling have demonstrated that post resuscitation cooling is generally safe in intensive care, and reduces death or disability at 18 months of age after neonatal encephalopathy. These studies, however, show that only a subset of babies seemed to benefit. The challenge for the future is to find ways of improving the effectiveness of treatment.

Combination of systemic hypothermia and N-acetylcysteine attenuates hypoxic-ischemic brain injury in neonatal rats

Hypoxic ischemic (HI) injury in neonates may have devastating, long-term consequences. Recently completed clinical trials in HI neonates indicate that hypothermia within 6 h of birth results in modest improvement in the combined outcome of death or severe disability. The aim of this study was to investigate the effects of combining hypothermia and N-acetylcysteine (NAC) on brain injury, neonatal reflexes and myelination after neonatal HI. Seven-day-old rats were subjected to right common carotid artery ligation and hypoxia (8% oxygen) for 2 h. Systemic hypothermia (30 + 0.5 degrees C) was induced immediately after the period of HI and was maintained for 2 h. NAC (50 mg/kg) was administered by intraperitoneal injection daily until sacrifice. Brain infarct volumes were significantly reduced at 48 h post-HI in the hypothermia plus NAC group (21.5 +/- 3.84 mm3) compared with vehicle (240.85 +/- 4.08 mm3). Neonatal reflexes were also significantly improved by combination therapy at days 1 and 7. There was a significant loss of right hemispheric brain volume in the untreated group at 2 and 4 wk after HI insult. Brain volumes were preserved in hypothermia plus NAC group and were not significantly different when compared with the sham group. Similarly, increased myelin expression was seen in brain sections from hypothermia plus NAC group, when stained for Luxol Fast Blue (LFB), Myelin Basic Protein (MBP) and Proteolipid protein (PLP). These results indicate that hypothermia plus NAC combination therapy improves infarct volume, myelin expression and functional outcomes after focal HI injury.

Resuscitative hypothermia protects the neonatal rat brain from hypoxic-ischemic injury

The effect of 24 h of hypothermic recovery on moderate hypoxic-ischemic brain damage in P7-rats was investigated for 42 d after the insult, using magnetic resonance and histopathology. Occlusion of right common carotid artery and 90 min exposure to 8% O2 at 37 degrees C body temperature produced cytotoxic edema of 51(+/-11)% brain volume (BV) and depression of brain energy metabolism (PCr/Pi) from 1.43(+/-0.21) to 0.14(+/-0.11). During recovery, the body temperature was reduced to 30 degrees C for 24 h in 36 animals, but was kept at 37 degrees C in 34 animals. The edema waned upon reoxygenation leaving only the core lesion at 2 h, but reappeared reaching a maximal extent of 11+/-8% BV under hypothermia compared to 45(+/-10)% under normothermia at around 24 h. PCr/Pi recovered transiently within 13 h and declined again to 1.07(+/-0.19) under hypothermia and to 0.48(+/-0.22) under normothermia at around 24 h. Hypothermia led to significant long term brain protection, leaving permanent tissue damage of 12(+/-6)% BV compared to 35(+/-12)% BV under normothermia. However, animals with severe initial injury developed large infarctions, despite hypothermic treatment. Even then, the time to develop infarction was significantly prolonged, leaving the opportunity for additional therapeutic intervention.

Modest hypothermia as a neuroprotective strategy in high-risk term infants

This article briefly reviews the pathogenesis of hypoxic-ischemic cerebral injury, the experimental data, and clinical studies that have evaluated the potential therapeutic benefit of modest selective or whole body hypothermia in reducing the subsequent development of irreversible brain injury without untoward side effects. Data are insufficient to recommend routine use of either modest selective or whole body hypothermia after resuscitation of infants with suspected asphyxia. Further clinical trials are needed to determine which infants would benefit most and which method of cooling would be most effective.

Therapeutic hypothermia: from lab to NICU

The possibility of a therapeutic role for cerebral hypothermia during or after resuscitation from perinatal asphyxia has been a long-standing focus of research. However, early studies had limited and contradictory results. It is now known that severe hypoxia-ischemia may not cause immediate cell death, but may precipitate a complex biochemical cascade leading to the delayed development of neuronal loss. These phases include a latent phase after reperfusion, with initial recovery of cerebral energy metabolism but EEG suppression, followed by a secondary phase characterized by accumulation of cytotoxins, seizures, cytotoxic edema, and failure of cerebral oxidative metabolism from 6 to 15 h post insult. Although many of the secondary processes can be injurious, they appear to be primarily epiphenomena of the 'execution' phase of cell death. This conceptual framework allows a better understanding of the experimental parameters that determine effective hypothermic neuroprotection, including the timing of initiation of cooling, its duration and the depth of cooling attained. Moderate cerebral hypothermia initiated in the latent phase, between one and as late as 6 h after reperfusion, and continued for a sufficient duration in relation to the severity of the cerebral injury, has been consistently associated with potent, long-lasting neuroprotection in both adult and perinatal species. The results of the first large multicentre randomized trial of head cooling for neonatal encephalopathy and previous phase I and II studies now strongly suggest that prolonged cerebral hypothermia is both generally safe - at least in an intensive care setting - and can improve intact survival up to 18 months of age. Both long-term followup studies and further large studies of whole body cooling are in progress.

Whole-body hypothermia for neonates with hypoxic-ischemic encephalopathy

BACKGROUND

Hypothermia is protective against brain injury after asphyxiation in animal models. However, the safety and effectiveness of hypothermia in term infants with encephalopathy is uncertain.

METHODS

We conducted a randomized trial of hypothermia in infants with a gestational age of at least 36 weeks who were admitted to the hospital at or before six hours of age with either severe acidosis or perinatal complications and resuscitation at birth and who had moderate or severe encephalopathy. Infants were randomly assigned to usual care (control group) or whole-body cooling to an esophageal temperature of 33.5 degrees C for 72 hours, followed by slow rewarming (hypothermia group). Neurodevelopmental outcome was assessed at 18 to 22 months of age. The primary outcome was a combined end point of death or moderate or severe disability.

RESULTS

Of 239 eligible infants, 102 were assigned to the hypothermia group and 106 to the control group. Adverse events were similar in the two groups during the 72 hours of cooling. Primary outcome data were available for 205 infants. Death or moderate or severe disability occurred in 45 of 102 infants (44 percent) in the hypothermia group and 64 of 103 infants (62 percent) in the control group (risk ratio, 0.72; 95 percent confidence interval, 0.54 to 0.95; P=0.01). Twenty-four infants (24 percent) in the hypothermia group and 38 (37 percent) in the control group died (risk ratio, 0.68; 95 percent confidence interval, 0.44 to 1.05; P=0.08). There was no increase in major disability among survivors; the rate of cerebral palsy was 15 of 77 (19 percent) in the hypothermia group as compared with 19 of 64 (30 percent) in the control group (risk ratio, 0.68; 95 percent confidence interval, 0.38 to 1.22; P=0.20).

CONCLUSIONS

Whole-body hypothermia reduces the risk of death or disability in infants with moderate or severe hypoxic-ischemic encephalopathy.

Depth of delayed cooling alters neuroprotection pattern after hypoxia-ischemia

Hypothermia after perinatal hypoxia-ischemia (HI) is neuroprotective; the precise brain temperature that provides optimal protection is unknown. To assess the pattern of brain injury with 3 different rectal temperatures, we randomized 42 newborn piglets: (Group i) sham-normothermia (38.5-39 degrees C); (Group ii) sham-33 degrees C; (Group iii) HI-normothermia; (Group iv) HI-35 degrees C; and (Group v) HI-33 degrees C. Groups iii through v were subjected to transient HI insult. Groups ii, iv, and v were cooled to their target rectal temperatures between 2 and 26 hours after resuscitation. Experiments were terminated at 48 hours. Compared with normothermia, hypothermia at 35 degrees C led to 25 and 39% increases in neuronal viability in cortical gray matter (GM) and deep GM, respectively (both p < 0.05); hypothermia at 33 degrees C resulted in a 55% increase in neuronal viability in cortical GM (p < 0.01) but no significant increase in neuronal viability in deep GM. Comparing hypothermia at 35 and 33 degrees C, 35 degrees C resulted in more viable neurons in deep GM, whereas 33 degrees C resulted in more viable neurons in cortical GM (both p < 0.05). These results suggest that optimal neuroprotection by delayed hypothermia may occur at different temperatures in the cortical and deep GM. To obtain maximum benefit, you may need to design patient-specific hypothermia protocols by combining systemic and selective cooling.