Post-hypoxic hypothermia reduces cerebrocortical release of NO and excitotoxins

Resuscitation with 100% oxygen increases injury and counteracts the neuroprotective effect of therapeutic hypothermia in the neonatal rat

INTRODUCTION

Mild therapeutic hypothermia (HT) reduces brain injury in survivors after perinatal asphyxia. Recent guidelines suggest that resuscitation of term infants should be started with air, but supplemental oxygen is still in use. It is not known whether supplemental oxygen during resuscitation affects the protection offered by subsequent HT.

RESULTS

Wilcoxon median (95% confidence interval) hippocampal injury scores (range 0.0-4.0; 0 to ≥90% injury) were 21% O(2) normothermia (NT): 2.00 (1.25-2.50), 21% O(2) HT: 1.00 (0.50-1.50), 100% O(2) NT: 2.50 (1.50-3.25), and 100% O(2) HT: 2.00 (1.25-2.50). Although HT significantly reduced hippocampal injury (B = -0.721, SEM = 0.297, P = 0.018), reoxygenation with 100% O(2) increased injury (B = +0.647, SEM = 0.297, P = 0.033). Regression constant B = 1.896, SEM = 0.257 and normally distributed residuals.

DISCUSSION

We confirm an ~50% neuroprotective effect of therapeutic HT in the neonatal rat. Reoxygenation with 100% O(2) increased injury and worsened reflex performance. HT was neuroprotective whether applied after reoxygenation with air or 100% O(2). However, HT after 100% O(2) gave no net neuroprotection.

METHODS

In an established neonatal rat model, hypoxia-ischemia (HI) was followed by 30-min reoxygenation in either 21% O(2) or 100% O(2) before 5 h of NT (37 °C) or HT (32 °C). The effects of HT and 100% O(2) on histopathologic injury in the hippocampus, basal ganglia, and cortex, and on postural reflex performance 7 d after the insult, were estimated by linear regression.

Differential effect of intrauterine hypoxia on caspase 3 and DNA fragmentation in fetal guinea pig hearts and brains

The aim of this study is to quantify the effect of intrauterine hypoxia (HPX) and the role of nitric oxide (NO) on the apoptotic enzyme, caspase 3, and DNA fragmentation in fetal heart and brain. Hypoxia and NO are important regulators of apoptosis, although this has been little studied in the fetal organs. We investigated the effect of intrauterine HPX on apoptosis and the role of NO in both fetal hearts and brains. Pregnant guinea pigs were exposed to room temperature (N = 14) or 10.5% O₂ (N = 12) for 14 days prior to term (term = 65 days) and administered water or L-N6-(1-iminoethyl)-lysine (LNIL), an inducible nitric oxide synthase (iNOS) inhibitor, for 10 days. Fetal hearts and brains were excised from anesthetized near-term fetuses for study. Chronic HPX decreased pro- and active caspase 3, caspase 3 activity, and DNA fragmentation levels in fetal hearts compared with normoxic controls. L-N6-(1-iminoethyl)-lysine prevented the HPX-induced decrease in caspase 3 activity but did not alter DNA fragmentation levels. In contrast, chronic HPX increased both apoptotic indices in fetal brains, which were inhibited by LNIL. Thus, the effect of HPX on apoptosis differs between fetal organs, and NO may play an important role in modulating these effects.

Treatment advances in neonatal neuroprotection and neurointensive care

Knowledge of the nature, prognosis, and ways to treat brain lesions in neonatal infants has increased remarkably. Neonatal hypoxic-ischaemic encephalopathy (HIE) in term infants, mirrors a progressive cascade of excito-oxidative events that unfold in the brain after an asphyxial insult. In the laboratory, this cascade can be blocked to protect brain tissue through the process of neuroprotection. However, proof of a clinical effect was lacking until the publication of three positive randomised controlled trials of moderate hypothermia for term infants with HIE. These results have greatly improved treatment prospects for babies with asphyxia and altered understanding of the theory of neuroprotection. The studies show that moderate hypothermia within 6 h of asphyxia improves survival without cerebral palsy or other disability by about 40% and reduces death or neurological disability by nearly 30%. The search is on to discover adjuvant treatments that can further enhance the effects of hypothermia.

Bilateral middle cerebral artery thromboembolic occlusion. Could maternal hyperthermia be a detrimental factor?

We describe a six-month-old girl with microcephaly, developmental delay, truncal hypotonia, left pyramidal signs, partial seizures and myoclonic spasms, born to a feverish mother. MRI showed bilateral vascular lesions in the territory of the middle cerebral arteries, prevalent in the right hemisphere, together with hypoplasia of the posterior part of the corpus callosum and Wallerian degeneration of the cerebral peduncle. There may be many reasons for these lesions. In the reported patient the presence of maternal hyperthermia could have exacerbated cerebral thromboembolic occlusion.

Current management of the infant who presents with neonatal encephalopathy

Neonatal encephalopathy after perinatal hypoxic-ischemic insult is a major contributor to global child mortality and morbidity. Brain injury in term infants in response to hypoxic-ischemic insult is a complex process evolving over hours to days, which provides a unique window of opportunity for neuroprotective treatment interventions. Advances in neuroimaging, brain monitoring techniques, and tissue biomarkers have improved the ability to diagnose, monitor, and care for newborn infants with neonatal encephalopathy as well as predict their outcome. However, challenges remain in early identification of infants at risk for neonatal encephalopathy, determination of timing and extent of hypoxic-ischemic brain injury, as well as optimal management and treatment duration. Therapeutic hypothermia is the most promising neuroprotective intervention to date for infants with moderate to severe neonatal encephalopathy after perinatal asphyxia and has currently been incorporated in many neonatal intensive care units in developed countries. However, only 1 in 6 babies with encephalopathy will benefit from hypothermia therapy; many infants still develop significant adverse outcomes. To enhance the outcome, specific diagnostic predictors are needed to identify patients likely to benefit from hypothermia treatment. Studies are needed to determine the efficacy of combined therapeutic strategies with hypothermia therapy to achieve maximal neuroprotective effect. This review focuses on important concepts in the pathophysiology, diagnosis, and management of infants with neonatal encephalopathy due to perinatal asphyxia, including an overview of recently introduced novel therapies.

Mechanisms of hypothermic neuroprotection

There is now compelling clinical evidence that 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 subsequent neuronal loss and improve behavioral recovery in term infants and adults after cardiac arrest. Perhaps surprisingly, the specific mechanisms of hypothermic neuroprotection remain unclear, at least in part because hypothermia suppresses a broad range of potential injurious factors. In the present review we critically examine proposed mechanisms in relation to the known window of opportunity for effective protection with hypothermia. Better knowledge of the mechanisms of hypothermia is critical to help guide the rational development of future combination treatments to augment neuroprotection with hypothermia, and to identify those most likely to benefit from it.

Reduced expression of DNA glycosylases in post-hypoxic newborn pigs undergoing therapeutic hypothermia

Supplementary oxygen during resuscitation of the asphyxiated newborn is associated with increased generation of reactive oxygen species and oxidative stress. It is suspected that hyperoxic reoxygenation may cause increased damage to DNA, resulting in replication errors, and cell death or potential fixation of mutations if unrepaired. Therapeutic hypothermia may attenuate the development of brain damage after asphyxia, but it is not known how post-hypoxic hyperoxia and hypothermia affect accumulation of DNA-damage and DNA repair. Anaesthetised newborn pigs were randomised to control (n=6) or severe global hypoxia (n=46). After 20min of reoxygenation with either room air or 100% O(2), followed by 6.5h of normothermia (deep rectal temperature 39°C) or total body cooling (35°C), oxidative DNA damage (8-hydroxy-2'-deoxyguanosine) in brain, liver and urine, and transcription of DNA repair glycosylases (NEIL1, NEIL3, and OGG1) in brain and liver were measured. Hypoxic pigs displayed increased urinary 8-oxodG levels: mean (SD) 8-oxodG/creatinine was 3.55 (1.46) vs. control 2.02 (0.53), p<0.05, but levels were not affected by hyperoxia or hypothermia. Accumulation of 8-oxodG in the brain and liver did not differ across groups. Post-hypoxic transcription of DNA glycosylases was down-regulated by hypothermia: OGG1 in hippocampus and liver (p<0.01); NEIL1 in hippocampus (p<0.01), cortex and striatum (p<0.05) and liver (p<0.001); and NEIL3 in hippocampus (p<0.01) and cerebellum (p<0.001). Hyperoxia did not affect transcription of glycosylases in the brain. We confirm increased oxidative stress after hypoxia. DNA repair glycosylases were down-regulated by hypothermia but with no effect on accumulation of oxidative damage in genomic DNA.

Xenon enhances hypothermic neuroprotection in asphyxiated newborn pigs

OBJECTIVE

To investigate whether inhaling 50% xenon during hypothermia (HT) offers better neuroprotection than xenon or HT alone.

METHODS

Ninety-eight newborn pigs underwent a 45-minute global hypoxic-ischemic insult severe enough to cause permanent brain injury, and 12 pigs underwent sham protocol. Pigs then received intravenous anesthesia and were randomized to 6 treatment groups: (1) normothermia (NT; rectal temperature 38.5 degrees C, n = 18); (2) 18 hours 50% xenon with NT (n = 12); (3) 12 hours HT (rectal temperature 33.5 degrees C, n = 18); (4) 24 hours HT (rectal temperature 33.5 degrees C, n = 17); (5) 18 hours 50% xenon with 12 hours HT (n = 18); and (6) 18 hours 50% xenon with 24 hours HT (n = 17). Fifty percent xenon was administered via a closed circle with 30% oxygen and 20% nitrogen. After 10 hours rewarming, cooled pigs remained normothermic until terminal perfusion fixation at 72 hours. Global and regional brain neuropathology and clinical neurological scores were performed.

RESULTS

Xenon (p = 0.011) and 12 or 24 hours HT (p = 0.003) treatments offered significant histological global, and regional neuroprotection. Combining xenon with HT yielded an additive neuroprotective effect, as there was no interaction effect (p = 0.54). Combining Xenon with 24 hours HT offered 75% global histological neuroprotection with similarly improved regional neuroprotection: thalamus (100%), brainstem (100%), white matter (86%), basal ganglia (76%), cortical gray matter (74%), cerebellum (73%), and hippocampus (72%). Neurology scores improved in the 24-hour HT and combined xenon HT groups at 72 hours.

INTERPRETATION

Combining xenon with HT is a promising therapy for severely encephalopathic infants, doubling the neuroprotection offered by HT alone.

Early protective effect of hypothermia in newborn pigs after hyperoxic, but not after normoxic, reoxygenation

Abstract Mild hypothermia can attenuate the development of brain damage after asphyxia. Supplemental oxygen during resuscitation increases generation of reactive oxygen species, compared to room air. It is unknown if supplemental oxygen affects hypothermic neuroprotection. We studied the early effects of hyperoxic reoxygenation and subsequent hypothermia on tissue oxygenation, microcirculation, inflammation and brain damage after global hypoxia. Anesthetized newborn pigs were randomized to control (n=6), or severe global hypoxia (n=46). Three pigs died during hypoxia or reoxygenation. After 20-min reoxygenation with room air (n=22) or 100% oxygen (n=21), pigs were randomized to normothermia (deep rectal temperature 39 degrees C, n=22) or total body cooling (35 degrees C, n=21) for 6.5 h before the experiment was terminated. We demonstrated a differential effect of post-hypoxic hypothermia between animals reoxygenated with 100% oxygen and with room air, with reduced damage only in hypothermic animals reoxygenated with 100% oxygen (P=0.001). Hyperoxic reoxygenation resulted in a significant overshoot in striatal oxygen tension, without affecting microcirculation. Inflammatory response after the insult did not differ between groups. The results indicate an early protective effect of hypothermia which may vary with oxygen level used during reoxygenation.

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.

Hypoxic-ischemic encephalopathy in the term infant

Hypoxia-ischemia in the perinatal period is an important cause of cerebral palsy and associated disabilities in children. There has been significant research progress in hypoxic-ischemic encephalopathy over the last 2 decades, and many new molecular mechanisms have been identified. Despite all these advances, therapeutic interventions are still limited. In this article the authors discuss several molecular pathways involved in hypoxia-ischemia, and potential therapeutic targets.

Topiramate concentrations in neonates treated with prolonged whole body hypothermia for hypoxic ischemic encephalopathy

PURPOSE

Therapeutic hypothermia reduces mortality and neurologic impairment in neonates with hypoxic-ischemic encephalopathy. Topiramate exerts a neuroprotective effect in asphyxiated neonatal animal models. However, no studies have investigated the association of hypothermia and topiramate, because topiramate pharmacokinetics during hypothermia and the optimal administration schedule are unknown. The influence of hypothermia on topiramate pharmacokinetics was evaluated in asphyxiated neonates treated with prolonged whole-body hypothermia and topiramate.

METHODS

Thirteen term newborns were treated with mild or deep whole body hypothermia for 72 h; all received oral topiramate, 5 mg/kg once a day for the first 3 days of life, and seven had concomitant phenobarbital treatment. Topiramate concentrations were measured on serial dried blood spots.

RESULTS

Topiramate concentrations were within the reference range in 11 of 13 newborns, whereas concentrations exceeded the upper limit in 2 of 13, both newborns on deep hypothermia. Topiramate concentrations reached a virtual steady state in nine newborns, for whom pharmacokinetic parameters were calculated. Values of topiramate maximal and minimal concentration, half-life, average concentration, and area under the time-concentration curve resulted in considerably higher values than those reported in normothermic infants. With respect to normothermic infants, time of maximal concentration was mildly delayed and apparent total body clearance was lower, suggesting slower absorption and elimination. Pharmacokinetic parameters did not differ significantly between infants on deep versus mild hypothermia and in those on topiramate monotherapy versus add-on phenobarbital.

CONCLUSION

Most neonates on prolonged hypothermia treated with topiramate 5 mg/kg once a day exhibited drug concentrations within the reference range for the entire treatment duration.

Effect of hypothermia therapy after outpatient cardiac arrest due to ventricular fibrillation

BACKGROUND

Several investigators have emphasized the positive effect of hypothermia therapy on patients who have suffered from cardiac arrest. Salvaging patients from circulatory collapse is a pivotal task, but it is unclear whether additional hypothermia can practically contribute to an improvement in the neurological outcome.

METHODS AND RESULTS

Since December 2005, our hospital has been using hypothermia therapy. Forty-six comatose patients after recovery of spontaneous circulation were consecutively enrolled in the present study. Twenty-five of the enrolled patients received hypothermia therapy and 21 did not because they were treated prior to 2005. The time from collapse to spontaneous circulation (P=0.09), the rates of performance of bystander CPR (P=0.370) and presence of a witnessed collapse (P=0.067) were not significantly different between the recovery group (n=28) and the non-recovery group (n=18). The additional hypothermia therapy was an independent predictor of neurological recovery (P=0.005, OR 6.5, 95%CI 1.74-24.27). The recovery rate was significantly higher in patients who received hypothermia therapy (80%) compared to those who did not (38%).

CONCLUSIONS

Hypothermia therapy is very useful for treating patients who have had an out-of-hospital cardiac arrest; it should be induced rapidly and smoothly.

Effects of therapeutic hypothermia on multiorgan dysfunction in asphyxiated newborns: whole-body cooling versus selective head cooling

OBJECTIVE

Multiorgan dysfunction in asphyxiated newborns receiving therapeutic hypothermia achieved by either selective head cooling (SHC) or whole-body cooling (WBC) has not been well characterized. The beneficial effect of SHC in organs other than the brain may potentially be limited because unlike WBC, SHC aims to achieve effective brain cooling with less-systemic hypothermia. However, the relative effects of SHC and WBC with currently available cooling protocols on multiorgan dysfunction are unknown.The aim of this study was to compare the multiorgan dysfunction in infants receiving therapeutic hypothermia induced by either SHC or WBC.

STUDY DESIGN

In 59 asphyxiated newborns who received therapeutic hypothermia by either SHC (n=31) or WBC (n=28), the severity of pulmonary, hepatic and renal dysfunction and coagulopathy and electrolyte disturbances were assessed before the start of cooling (baseline), and at specific time intervals (24, 48 and 72 h) throughout cooling. Enrollment criteria, clinical monitoring and treatment during cooling, whether SHC or WBC, were similar, as reported earlier.

RESULT

The presence of clinical respiratory distress, along with the need for ventilatory support for varying duration during cooling, was similar in both the WBC and SHC groups (100 vs 94%, P=0.49, OR 1.9, 95% CI 1.5-2.5). The use of fresh frozen plasma and platelet transfusion to treat coagulopathy and thrombocytopenia was similar (WBC 48% vs SHC 58%, P=0.59, OR 0.7, 95% CI 0.2-1.9, and WBC 41% vs SHC 32%, P=0.58, OR 1.4, 95% CI 0.5-4.2, respectively), and equivalent numbers of infants from both groups were treated with vasopressors for >24 h (WBC 59% vs SHC 55%, P=0.79, OR 1.2, 95% CI 0.4-3.4). The incidence of oliguria (urine output <0.5 ml kg(-1) h(-1) for >24 h after birth) and rising serum creatinine (with maximum serum creatinine >0.9 mg dl(-1)) was also similar (WBC 18% vs SHC 39%, P=0.15, OR 0.4, 95% CI 0.1-1.3, and WBC 48% vs SHC 58%, P=0.59, OR 0.7, 95% CI 0.2-1.9, respectively). Laboratory parameters to assess the differential effect of WBC versus SHC on multiorgan dysfunction during 72 h of cooling, which include serum transaminases (serum aspartate aminotransferase and alanine aminotransferase), prothrombin time, partial thromboplastin time, INR, platelet counts, serum creatinine, serum sodium, serum potassium and serum calcium, were similar between the groups at the initiation of cooling and did not differ with the method of cooling.

CONCLUSION

Multiorgan system dysfunction in asphyxiated newborns during cooling remains similar for both cooling methods. Concerns regarding a differential effect of WBC versus SHC on multiorgan dysfunction, other than of the brain, should not be a consideration in selecting a method to produce therapeutic hypothermia.

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.

Hypothermia for hypoxic-ischemic encephalopathy

We are entering an era in which hypothermia will be used in combination with other novel neuroprotective interventions. The targeting of multiple sites in the cascade leading to brain injury may prove to be a more effective treatment strategy after hypoxic-ischemic encephalopathy in newborn infants than hypothermia alone.

Hypothermia and hypoxic-ischemic encephalopathy: guideline development using the best evidence

BABY AVA WAS DELIVERED AT 39 weeks gestation by emergency cesarean section following a prolapsed cord. Her mother was 23 years old, and this was her first pregnancy, which had been uneventful. She was Group B Streptococcus negative. The mother’s membranes ruptured one hour prior to arrival at the hospital, and she presented in labor. She was afebrile with stable vital signs. When initially examined, the cord was found prolapsed in the vaginal canal. She was immediately placed in a knee-chest posture and rushed to the operating room.

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

Background

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

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

Methods/Design

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

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

Sample size

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

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

Primary outcome

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

• Bayley mental developmental scale score less than 70

• Gross Motor Function Classification System Levels III – V

• Bilateral cortical visual impairments

Trial Registration

Current Controlled Trials ISRCTN89547571

Xenon and hypothermia combine additively, offering long-term functional and histopathologic neuroprotection after neonatal hypoxia/ischemia

BACKGROUND AND PURPOSE

Hypoxic/ischemic (HI) brain injury affects 1 to 6 per 1000 live human births, with a mortality of 15% to 20%. A quarter of survivors have permanent disabilities. Hypothermia is the only intervention that improves outcome; however, further improvements might be obtained by combining hypothermia with additional treatments. Xenon is a noble anesthetic gas with an excellent safety profile, showing great promise in vitro and in vivo as a neuroprotectant. We investigated combinations of 50% xenon (Xe(50%)) and hypothermia of 32 degrees C (HT(32 degrees C)) as a post-HI therapy.

METHODS

An established neonatal rat HI model was used. Serial functional neurologic testing into adulthood 10 weeks after injury was performed, followed by global and regional brain histopathology evaluation.

RESULTS

In the combination Xe(50%)HT(32 degrees C) group, complete restoration of long-term functional outcomes was seen. Hypothermia produced improvement on short- (P<0.001) and long- (P<0.001) term functional testing, whereas Xe(50%) alone predominantly improved long-term function (P<0.05), suggesting that short-term testing does not always predict eventual outcome. Similarly, the Xe(50%)HT(32 degrees C) combination produced the greatest (71%) improvement in global histopathology scores, a pattern mirrored in the regional scores, whereas Xe(50%) and HT(32 degrees C) individually produced smaller improvements (P<0.05 and P<0.001, respectively). The interaction between the 2 treatments was additive.

CONCLUSIONS

The xenon/hypothermia combination additively confers greater protection after HI than either treatment alone. The functional improvement is almost complete, is sustained long term, and is accompanied by greatly improved histopathology. The unique safety profile differentiates xenon as an attractive combination therapy with hypothermia to improve the otherwise bleak outcome from neonatal HI.

Pathological apoptosis in the developing brain

More than half of the initially-formed neurons are deleted in certain brain regions during normal development. This process, whereby cells are discretely removed without interfering with the further development of remaining cells, is called programmed cell death (PCD). The term apoptosis is used to describe certain morphological manifestations of PCD. Many of the effectors of this developmental cell death program are highly expressed in the developing brain, making it more susceptible to accidental activation of the death machinery, e.g. following hypoxia-ischemia or irradiation. Recent evidence suggests, however, that activation and regulation of cell death mechanisms under pathological conditions do not exactly mirror physiological, developmentally regulated PCD. It may be argued that the conditions after e.g. ischemia are not even compatible with the execution of PCD as we know it. Under pathological conditions cells are exposed to various stressors, including energy failure, oxidative stress and unbalanced ion fluxes. This results in parallel triggering and potential overshooting of several different cell death pathways, which then interact with one another and result in complex patterns of biochemical manifestations and cellular morphological features. These types of cell death are here called "pathological apoptosis," where classical hallmarks of PCD, like pyknosis, nuclear condensation and caspase-3 activation, are combined with non-PCD features of cell death. Here we review our current knowledge of the mechanisms involved, with special focus on the potential for therapeutic intervention tailored to the needs of the developing brain.

Cerebral palsy

Cerebral palsy (CP) is a group of disorders of movement and posture resulting from nonprogressive disturbances of the fetal or neonatal brain. More than 80% of cases of CP in term infants originate in the prenatal period; in premature infants, both prenatal or postnatal causes contribute. The most prevalent pathological lesion seen in CP is periventricular white matter injury (PWMI) resulting from vulnerability of the immature oligodendrocytes (pre-OLs) before 32 wk of gestation. PWMI is responsible for the spastic diplegia form of CP and a spectrum of cognitive and behavioral disorders. Oxidative stress and excitotoxicity resulting from excessive stimulation of ionotropic glutamate receptors on preOLs are the most prominent molecular mechanisms for PWMI. Asphyxia around the time of birth in term infants accounts for less than 15% of CP in developed countries but the incidence is higher in underdeveloped areas. Asphyxia causes a different pattern of brain injury and CP than is seen after preterm injuries. This type of CP is associated with the clinical syndrome of hypoxic-ischemic encephalopathy shortly after the insult, and the cortex, basal ganglia, and brainstem are selectively vulnerable to injury. Experimental models indicate that neurons in the neonatal brain are more likely to die by delayed apoptosis extending over days to weeks than those in the adult brain. Neurons die by glutamate-mediated excitotoxicity involving downstream caspase-dependent and caspase-independent cell death pathways. Recent reports indicate that males and females preferentially utilize different pathways. Clinical trials indicate that mild hypothermia reduces death or disability in term infants following asphyxia and basic research suggests that this approach might be combined with pharmacological strategies in the future.

Biopterin in the acute phase of hypoxia-ischemia in a neonatal pig model

To clarify the participation of inducible NOS (iNOS) in the hypoxia-ischemia, we examined iNOS and its tetrahydrobiopterin co-factor in the cerebral cortex and plasma in a newborn-piglet model. We also investigated the role of hypothermia in iNOS expression and biopterin production. Male newborn piglets were ventilated 6% oxygen for 45 min. Their common carotid arteries were clamped during hypoxia. Then they were resuscitated with 30% oxygen (HI group). Piglets of the hypothermia group were treated as the HI group and their body was cooled to 35.5 degrees C after hypoxic-ischemic insults. Sham-treated piglets were also reserved. In the HI group, iNOS was present in neurons and macrophages of the cerebral cortex 12h after the insult. The concentrations of nitrite and nitrate were elevated in the cerebral cortex 12h after hypoxic-ischemic insults but the biopterin level was unchanged. The plasma biopterin concentration after the insult (377.9+/-78.7 nM) was five times higher than before the insult (80.1+/-4.3 nM); this level peaked 4h after the insult (604.8+/-200.9 nM) and only slightly decreased after 12h (445.9+/-57.8 nM). In the hypothermia group, no iNOS expression was observed 12h after the insult. The plasma biopterin concentration after the insult (464.2+/-92.3 nM) was similar to that in the HI group, but was suppressed by 4h of hypothermia (229.3+/-106.8 nM). In this study, neuronal iNOS expression and increase of NO production were found in the acute phase of hypoxia-ischemia. Brain biopterin did not increase in hypoxia-ischemia although plasma biopterin was five-fold elevated. The discrepancy may also affect hypoxic-ischemic organ damage.

Hypothermia as a treatment for birth asphyxia

This chapter will report to the frequency of neonatal hypoxic-ischemic encephalopathy. The pathophysiology and the childhood outcome of encephalopathy due to hypoxia-ischemia will be examined. The limitations of current therapy for this condition and new therapies will be evaluated. Hypothermia seems to offer the most promise as a therapy for neuroprotection in hypoxic-ischemic encephalopathy. The evidence-based trials of hypothermia will be reviewed along with recommendations regarding clinical applications for this therapy and need for long-term follow-up of children receiving this therapy.

Pomegranate polyphenols and resveratrol protect the neonatal brain against hypoxic-ischemic injury

A previous study from our lab has shown that the polyphenol-rich pomegranate juice can protect the neonatal mouse brain against hypoxic-ischemic (H-I) injury when given to mothers in their drinking water. To test the hypothesis that this protection is due to the polyphenols in the juice, we studied the effects of the pomegranate polyphenol extract in the same neonatal H-I model. To further explore the role of a specific polyphenol in neonatal H-I we investigated the effects of resveratrol. The neuroprotective effects of resveratrol have been demonstrated in adult models of stroke, but had not previously been examined in neonates. We show that pomegranate polyphenols and resveratrol reduce caspase-3 activation following neonatal H-I. Resveratrol reduced caspase-3 activation when given before the injury but not when given 3 h after the injury. In addition to preventing caspase-3 activation, resveratrol also reduced calpain activation. Finally, we show that resveratrol can protect against tissue loss measured at 7 days after the injury. These and other recent findings suggest that polyphenols should be further investigated as a potential treatment to decrease brain injury due to neonatal H-I.

Rapid NMDA receptor phosphorylation and oxidative stress precede striatal neurodegeneration after hypoxic ischemia in newborn piglets and are attenuated with hypothermia

The basal ganglia of newborns are extremely vulnerable to hypoxic ischemia (HI). Striatal neurons undergo prominent necrosis after HI. The mechanisms for this degeneration are not well understood. Postasphyxic hypothermia ameliorates the striatal necrosis, but the mechanisms of hypothermia-induced neuroprotection are not known. We used a newborn piglet model of hypoxic-asphyxic cardiac arrest to test the hypotheses that N-methyl-d-aspartate receptor activation and free radical damage coexist, prior to neurodegeneration, early after resuscitation, and that these changes are attenuated with hypothermia. Piglets were subjected to 30min of hypoxia followed by 7min of airway occlusion, causing asphyxic cardiac arrest, and then were resuscitated and survived normothermically for 5min, 3h, or 6h, or hypothermically for 3h. By 6h of normothermic recovery, 50% of neurons in putamen showed ischemic cytopathology. Striatal tissue was fractionated into membrane or soluble proteins and was assayed by immunoblotting for carbonyl modification, phosphorylation of the N-methyl-d-aspartate receptor subunit NR1, and neuronal nitric oxide synthase. Significant accumulation of soluble protein carbonyls was present at 3h (196% of control) and 6h (142% of control). Phosphorylation of serine-897 of NR1 was increased significantly at 5min (161% of control) and 3h (226% of control) after HI. Phosphorylation of serine-890 of NR1 was also increased after HI. Membrane-associated neuronal nitric oxide synthase was increased by 35% at 5min. Hypothermia attenuated the oxidative damage and the NR1 phosphorylation in striatum. We conclude that neuronal death signaling in newborn striatum after HI is engaged rapidly through N-methyl-d-aspartate receptor activation, neuronal nitric oxide synthase recruitment, and oxidative stress. Postasphyxic, mild whole body hypothermia provides neuroprotection by suppressing N-methyl-d-aspartate receptor phosphorylation and protein oxidation.

Changes in laboratory parameters indicating cell necrosis and organ dysfunction in asphyxiated neonates on moderate systemic hypothermia

AIM

Asphyxia is a major cause of morbidity and mortality in term infants. In addition to cerebral injury other organs are also distressed due to hypoxic-ischaemic insult. Systemic hypothermia has a beneficial effect on brain injury. We tested the impact of hypothermia on hypoxic damage of other internal organs.

METHODS

Asphyxiated term neonates (n = 21) were randomised to groups treated with hypothermia (n = 12) and normothermia (n = 9). Hypothermia (33-34 degrees C) was initiated within 6 h of life, and maintained for 72 h. We determined serum transaminase, lactate dehydrogenase, creatine kinase, uric acid, creatinine levels and diuresis during 6, 24, 48 and 72 postnatal hours.

RESULTS

Area under curve values of aspartate aminotransferase (ASAT), lactate dehydrogenase (LDH), uric acid and creatinine during the investigated period and alanine aminotransferase (ALAT) value at 72 h were lower in neonates on hypothermia than in those on normothermia. Renal failure and liver impairment affected less hypothermic than normothermic neonates (3/12 vs. 7/9, p = 0.03, 3/12 vs. 6/9 p = 0.08, respectively). Four of the 12 hypothermic and 6 of the 9 normothermic neonates developed multiorgan failure.

CONCLUSIONS

These results suggest that systemic hypothermia may protect against cell necrosis and tissue dysfunction of internal organs after neonatal asphyxia.

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.

Induced cerebral hypothermia reduces post-hypoxic loss of phenotypic striatal neurons in preterm fetal sheep

Perinatal hypoxic-ischemic injury of the basal ganglia is a significant cause of disability in premature infants. Prolonged, moderate cerebral hypothermia has been shown to be neuroprotective after experimental hypoxia-ischemia; however, it has not been tested in the preterm brain. We therefore examined the effects of severe hypoxia and the potential neuroprotective effects of delayed hypothermia on phenotypic striatal neurons. Preterm (0.7 gestation) fetal sheep received complete umbilical cord occlusion for 25 min followed by cerebral hypothermia (fetal extradural temperature reduced from 39.4+/-0.3 degrees C to 29.5+/-2.6 degrees C) from 90 min to 70 h after the end of occlusion. Hypothermia was associated with a significant overall reduction in striatal neuronal loss compared with normothermia-occlusion fetuses (mean+/-SEM, 5.5+/-1.2% vs. 38.1+/-6.5%, P<0.01). Immunohistochemical studies showed that occlusion resulted in a significant loss of calbindin-28 kd, glutamic acid decarboxylase isoform 67 and neuronal nitric oxide synthase-immunopositive neurons (n=7, P<0.05), but not choline acetyltransferase-positive neurons, compared with sham controls (n=7). Hypothermia (n=7) significantly reduced the loss of calbindin-28 kd and neuronal nitric oxide synthase, but not glutamic acid decarboxylase-immunopositive neurons. In conclusion, delayed, prolonged moderate head cooling was associated with selective protection of particular phenotypic striatal projection neurons after severe hypoxia in the preterm fetus. These findings suggest that head cooling may help reduce basal ganglia injury in some premature babies.

Differential effects of hypothermia on early and late epileptiform events after severe hypoxia in preterm fetal sheep

Moderate cerebral hypothermia is consistently neuroprotective after experimental hypoxia-ischemia; however, its mechanisms remain poorly defined. Using a model of complete umbilical cord occlusion for 25 min in 0.7 gestation fetal sheep, we examined the effects of cerebral hypothermia (fetal extradural temperature reduced from 39.5 +/- 0.2 degrees C to <34 degrees C; mean +/- SD), from 90 min to 70 h after the end of the insult, on postocclusion epileptiform activity. In the first 6 h after the end of occlusion, fetal electroencephalographic (EEG) activity was abnormal with a mixture of fast and slow epileptiform transients superimposed on a suppressed background; seizures started a mean of 8 h after occlusion. There was a close correlation between numbers of these EEG transients and subsequent neuronal loss in the striatum after 3 days recovery (r(2) = 0.65, P = 0.008). Hypothermia was associated with a marked reduction in numbers of epileptiform transients in the first 6 h, reduced amplitude of seizures, and reduced striatal neuronal loss. In conclusion, neuroprotection with delayed, prolonged head cooling after a severe asphyxial insult in the preterm fetus was associated with potent, specific suppression of epileptiform transients in the early recovery phase but not of numbers of delayed seizures.

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.

Delayed whole-body cooling to 33 or 35 degrees C and the development of impaired energy generation consequential to transient cerebral hypoxia-ischemia in the newborn piglet

OBJECTIVES

Fundamental questions remain about the precise temperature providing optimal neuroprotection after perinatal hypoxia-ischemia (HI). Furthermore, if hypothermia delays the onset of the neurotoxic cascade and the secondary impairment in cerebral energy generation, the "latent phase" may be prolonged, thus extending the period when additional treatments may be effective. The aims of this study were to investigate the effects of delayed systemic cooling at either 33 degrees C or 35 degrees C on the following: (1) latent-phase duration, and (2) cerebral metabolism during secondary energy failure itself, in the 48-hour period after transient HI.

METHODS

Piglets were randomly assigned to the following: (1) HI-normothermic (HI-n) rectal temperature (Trectal; n = 12), (2) HI-Trectal 35 degrees C (HI-35; n = 7), and (3) HI-Trectal 33 degrees C (HI-33; n = 10). Groups were cooled to the target Trectal between 2 and 26 hours after HI. Serial magnetic resonance spectroscopy was performed over 48 hours. The effect of cooling on secondary energy failure severity (indexed by the nucleotide triphosphate/exchangeable phosphate pool [NTP/EPP] and phosphocreatine/inorganic phosphate [PCr/Pi] ratios) was assessed.

RESULTS

Compared with HI-n, HI-35 and HI-33 had a longer NTP/EPP latent phase and during the entire study duration had higher mean NTP/EPP and PCr/Pi. The latent phase (both PCr/Pi and NTP/EPP) and the whole-brain cerebral energetics were similar for HI-35 and HI-33. During the hypothermic period, compared with HI-n, PCr/Pi was preserved in the cooled groups, but this advantage was not maintained after rewarming. Compared with HI-n, HI-35 and HI-33 had higher NTP/EPP after rewarming.

CONCLUSIONS

Whole-body hypothermia for 24 hours at either 35 or 33 degrees C, commenced 2 hours after resuscitation, prolonged the NTP/EPP latent phase and reduced the overall secondary falls in mean PCr/Pi and NTP/EPP during 48 hours after HI. Reducing the temperature from 35 to 33 degrees C neither increased mean PCr/Pi and NTP/EPP nor further lengthened the latent phase.

Therapeutic hypothermia following perinatal asphyxia

Well constructed and carefully analysed trials of hypothermic neural rescue therapy for infants with neonatal encephalopathy have recently been reported. The data suggest that either selective head cooling or total body cooling reduces the combined chance of death or disability after birth asphyxia. However, as there are still unanswered questions about these treatments, many may still feel that further data are needed before health care policy can be changed to make cooling the standard of care for all babies with suspected birth asphyxia.

Free radicals, mitochondria, and hypoxia-ischemia in the developing brain

The immature brain is particularly susceptible to free radical injury because of its poorly developed scavenging systems and high availability of iron for the catalytic formation of free radicals. Neurons are more vulnerable to free radical damage than glial cells, but oligodendrocyte progenitors and immature oligodendrocytes in very prematurely born infants are selectively vulnerable to depletion of antioxidants and free radical attack. Reactive oxygen and nitrogen species play important roles in the initiation of apoptotic mechanisms and in mitochondrial permeability transition, and therefore constitute important targets for therapeutic intervention. Oxidative stress is an early feature after cerebral ischemia and experimental studies targeting the formation of free radicals demonstrate various degrees of protection after perinatal insults. Oxidative stress-regulated release of proapoptotic factors from mitochondria appears to play a much more important role in the immature brain. This review will summarize and compare with the adult brain some of the current knowledge of free radical formation in the developing brain and its roles in the pathophysiology after cerebral hypoxia-ischemia.

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.

Perinatal asphyxia, hyperthermia and hyperferremia as factors inducing behavioural disturbances in adulthood: A rat model

Alertness was studied in adult male Wistar rats after neonatal critical anoxia applied under three different thermal conditions: (i) at physiological neonatal body temperature of 33 degrees C, (ii) at body temperature elevated to 37 degrees C, and (iii) at body temperature elevated to 39 degrees C (both during anoxia and for 2 h postanoxia). To elucidate the effect of iron-dependent postanoxic oxidative damage to the brain, half of the group (iii) was injected with deferoxamine, a chelator of iron. Postanoxic behavioural disturbances were recorded in open-field, elevated plus-maze, and sudden silence tests when the rats reached the age of 4 month. Moreover, spontaneous motor activity of the rats was recorded radiotelemetrically in their home-cages. Both open-field stress-induced and spontaneous motor activity were reduced in rats subjected to neonatal anoxia under hyperthermic conditions. In contrast, these rats were hyperactive in the plus-maze test. Both the plus-maze and sudden silence tests revealed that these rats show reduced alertness to external stimuli signalling potential dangers. The behavioural disturbances were prevented by the body temperature of 33 degrees C and by postanoxic administration of deferoxamine. These data support the conclusion that permanent postanoxic behavioural disturbances are due to iron-dependent oxidative damage to the brain, which can be prevented by the reduced neonatal body temperature.

Hypothermia and amiloride preserve energetics in a neonatal brain slice model

A period of secondary energy failure consisting of a decline in phosphocreatine/inorganic phosphate (PCr/Pi), a rise in brain lactate, and alkaline intracellular pH (pH(i)) has been described in infants with neonatal encephalopathy. Strategies that ameliorate this energy failure may be neuroprotective. We hypothesized that a neonatal rat brain slice model undergoes a progressive decline in energetics, which can be ameliorated with hypothermia or amiloride. Interleaved phosphorus ((31)P) and proton ((1)H) magnetic resonance (MR) spectra were obtained from 350 microm neonatal rat brain slices over 8 h in a bicarbonate buffer at 37 degrees C and at 32 degrees C in 7- and 14-d models. (31)P MR spectra were obtained with amiloride in a bicarbonate-free buffer at 37 degrees C in the 14-d model. Findings were similar in 7- and 14-d models. In the 14-d model, there was a Pi doublet structure corresponding to alkaline pH(i) values of 7.50 +/- 0.02 and 7.21 +/- 0.04. Compared with the stabilized baseline of 100, at 5 h PCr/Pi was 65 +/- 6.3 and lactate/NAA was 187 +/- 3 at 37 degrees C, but PCr/Pi and lactate/NAA were not significantly different from baseline at 32 degrees C. Nucleotide triphosphate (NTP)/phosphomonoester (PME) was 0.93 +/- 0.23 at 37 degrees C and 1.81 +/- 0.21 at 32 degrees C at 5 h. With amiloride exposure in the 14-d model, baseline pH(i) values were 7.25 +/- 0.09 and 6.98 +/- 0.02 and NTP/PME was 1.81 +/- 0.05; these parameters were not significantly different at 5 h. Our interpretation of these findings is that the brain slice model underwent secondary energy failure, which was delayed with hypothermia or amiloride.

Therapeutic hypothermia for hypoxic–ischaemic encephalopathy in the newborn infant: review

PURPOSE OF REVIEW

This review examines recent findings from experimental models and clinical trials of induced hypothermia as treatment after cerebral hypoxia-ischaemia in term newborn infants.

RECENT FINDINGS

Experimental hypothermia inhibits many steps in the biochemical cascade that produces severe brain injury after hypoxia-ischaemia. This is in contrast to pharmacological agents, which tend to target only one step in the process that leads to brain injury. In adult humans hypothermia initiated immediately after cardiac arrest has improved outcomes. Delayed cooling after brain trauma has also been effective in a subgroup of adult patients. Seventy-two hours of selective head cooling with mild systemic hypothermia (rectal temperature 34.5 degrees C) in term infants with hypoxic-ischaemic encephalopathy (HIE) reduced death or disability in the infants with less severe electroencephalographic changes at entry (no benefit in those with advanced electroencephalographic changes). Cooling had no apparent adverse effects. A smaller randomized clinical trial of 48 h whole body cooling (rectal T 33 degrees C) found a reduction in death and neurological impairment.

SUMMARY

In term infants with HIE there is emerging evidence that both selective head cooling and whole body cooling are neuroprotective and safe. This is consistent with a wealth of experimental animal data and adult trials. Neuroprotection seems to be lost if cooling is started after 6 h. The challenge now is to complete ongoing trials. If meta-analysis confirms a therapeutic effect, then this may lead to selection criteria and treatment protocols for very early hypothermia in HIE at term.

Epileptiform activity during rewarming from moderate cerebral hypothermia in the near-term fetal sheep

Moderate hypothermia is consistently neuroprotective after hypoxic-ischemic insults and is the subject of ongoing clinical trials. In pilot studies, we observed rebound seizure activity in one infant during rewarming from a 72-h period of hypothermia. We therefore quantified the development of EEG-defined seizures during rewarming in an experimental paradigm of delayed cooling for cerebral ischemia. Moderate cerebral hypothermia (n=9) or sham cooling (n=13) was initiated 5.5 h after reperfusion from a 30-min period of bilateral carotid occlusion in near-term fetal sheep and continued for 72 h after the insult. During spontaneous rewarming, fetal extradural temperature rose from 32.5 +/- 0.6 degrees C to control levels (39.4 +/- 0.1 degrees C) in 47 +/- 6 min. Carotid blood flow and mean arterial blood pressure increased transiently during rewarming. The cooling group showed a significant increase in electrical seizure events 2, 3, and 5 h after rewarming, maximal at 2 h (2.9 +/- 1.2 versus 0.5 +/- 0.5 events/h; p <0.05). From 6 h after rewarming, there was no significant difference between the groups. Individual seizures were typically short (28.8 +/- 5.8 s versus 29.0 +/- 6.8 s in sham cooled; NS), and of modest amplitude (35.9 +/- 2.8 versus 38.8 +/- 3.4 microV; NS). Neuronal loss in the parasagittal cortex was significantly reduced in the cooled group (51 +/- 9% versus 91 +/- 5%; p <0.002) and was not correlated with rebound epileptiform activity. In conclusion, rapid rewarming after a prolonged interval of therapeutic hypothermia can be associated with a transient increase in epileptiform events but does not seem to have significant adverse implications for neural outcome.