Mild hypothermia after severe transient hypoxia-ischemia reduces the delayed rise in cerebral lactate in the newborn piglet

Temperature control after cardiac arrest

Managing temperature is an important part of post-cardiac arrest care. Fever or hyperthermia during the first few days after cardiac arrest is associated with worse outcomes in many studies. Clinical data have not determined any target temperature or duration of temperature management that clearly improves patient outcomes. Current guidelines and recent reviews recommend controlling temperature to prevent hyperthermia. Higher temperatures can lead to secondary brain injury by increasing seizures, brain edema and metabolic demand. Some data suggest that targeting temperature below normal could benefit select patients where this pathology is common. Clinical temperature management should address the physiology of heat balance. Core temperature reflects the heat content of the head and torso, and changes in core temperature result from changes in the balance of heat production and heat loss. Clinical management of patients after cardiac arrest should include measurement of core temperature at accurate sites and monitoring signs of heat production including shivering. Multiple methods can increase or decrease heat loss, including external and internal devices. Heat loss can trigger compensatory reflexes that increase stress and metabolic demand. Therefore, any active temperature management should include specific pharmacotherapy or other interventions to control thermogenesis, especially shivering. More research is required to determine whether individualized temperature management can improve outcomes.

Effects of xenon gas on human airway epithelial cells during hyperoxia and hypothermia

BACKGROUND

Hypothermia with xenon gas has been used to reduce brain injury and disability rate after perinatal hypoxia-ischemia. We evaluated xenon gas therapy effects in an in vitro model with or without hypothermia on cultured human airway epithelial cells (Calu-3).

METHODS

Calu-3 monolayers were grown at an air-liquid interface and exposed to one of the following conditions: 1) 21% FiO2 at 37°C (control); 2) 45% FiO2 and 50% xenon at 37°C; 3) 21% FiO2 and 50% xenon at 32°C; 4) 45% FiO2 and 50% xenon at 32°C for 24 hours. Transepithelial resistance (TER) measurements were performed and apical surface fluids were collected and assayed for total protein, IL-6, and IL-8. Three monolayers were used for immunofluorescence localization of zonula occludens-1 (ZO-1). The data were analyzed by one-way ANOVA.

RESULTS

TER decreased at 24 hours in all treatment groups. Xenon with hyperoxia and hypothermia resulted in greatest decrease in TER compared with other groups. Immunofluorescence localization of ZO-1 (XY) showed reduced density of ZO-1 rings and incomplete ring-like staining in the 45% FiO2- 50% xenon group at 32°C compared with other groups. Secretion of total protein was not different among groups. Secretion of IL-6 in 21% FiO2 with xenon group at 32°C was less than that of the control group. The secretion of IL-8 in 45% FiO2 with xenon at 32°C was greater than that of other groups.

CONCLUSION

Hyperoxia and hypothermia result in detrimental epithelial cell function and inflammation over 24-hour exposure. Xenon gas did not affect cell function or reduce inflammation.

Prospective qualification of early cerebral biomarkers in a randomised trial of treatment with xenon combined with moderate hypothermia after birth asphyxia

Background

The TOBY-Xe proof of concept randomised trial found no effect of xenon combined with hypothermia after birth asphyxia on the lactate to N-acetyl aspartate ratio (Lac/NAA) in the thalamus and fractional anisotropy (FA) in white matter tracts measured within 15 days of birth. To confirm that these biomarkers are qualified to predict long-term outcome after neural rescue therapy we assessed surviving participants at 2–3 years of age.

Methods

Of the 92 infants in TOBY-Xe, one was omitted from the study, 69 survived and we assessed 62 participants, 32 in the hypothermia and xenon and 30 in the hypothermia only groups. We examined the relation between Lac/NAA and FA and the scores of the Bayley Scales of Infant and Toddler Development III and calculated their predictive accuracy for moderate or severe disability or death.

Results

Fifteen of 62 participants (24%) developed moderate/severe disability, and 22/92 (24%) died.

The Lac/NAA ratio (difference in medians 0.628, 95% CI -0.392 to 4.684) and FA (difference in means −0.055, 95% CI -0.033 to −0.077) differed significantly between participants with or without moderate or severe disability or death and were significantly related with development scores in both groups. Adverse outcomes were correctly identified in 95.65% of cases by Lac/NAA and 78.79% by FA, with adequate mean calibration of the model.

Interpretation

The results confirm the qualification of the cerebral magnetic resonance biomarkers employed in the TOBY-Xe study as predictors of outcome after neuroprotective therapy.

Fund

The Centre for the Developing Brain, King's College London, UK.

Cerebral Lactate Concentration in Neonatal Hypoxic-Ischemic Encephalopathy: In Relation to Time, Characteristic of Injury, and Serum Lactate Concentration

Background

Cerebral lactate concentration can remain detectable in neonatal hypoxic-ischemic encephalopathy (HIE) after hemodynamic stability. The temporal resolution of regional cerebral lactate concentration in relation to the severity or area of injury is unclear. Furthermore, the interplay between serum and cerebral lactate in neonatal HIE has not been well defined. The study aims to describe cerebral lactate concentration in neonatal HIE in relation to time, injury, and serum lactate.

Design/methods

Fifty-two newborns with HIE undergoing therapeutic hypothermia (TH) were enrolled. Magnetic resonance imaging and spectroscopy (MRI + MR spectroscopy) were performed during and after TH at 54.6 ± 15.0 and 156 ± 57.6 h of life, respectively. Severity and predominant pattern of injury was scored radiographically. Single-voxel ¹H MR spectra were acquired using short-echo (35 ms) PRESS sequence localized to the basal ganglia (BG), thalamus (Thal), gray matter (GM), and white matter. Cerebral lactate concentration was quantified by LCModel software. Serum and cerebral lactate concentrations were plotted based on age at time of measurement. Multiple comparisons of regional cerebral lactate concentration based on severity and predominant pattern of injury were performed. Spearman's Rho was computed to determine correlation between serum lactate and cerebral lactate concentration at the respective regions of interest.

Results

Overall, serum lactate concentration decreased over time. Cerebral lactate concentration remained low for less severe injury and decreased over time for more severe injury. Cerebral lactate remained detectable even after TH. During TH, there was a significant higher concentration of cerebral lactate at the areas of injury and also when injury was more severe. However, these differences were no longer observed after TH. There was a weak correlation between serum lactate and cerebral lactate concentration at the BG (r_s = 0.3, p = 0.04) and Thal (r_s = 0.35, p = 0.02). However, in infants with moderate-severe brain injury, a very strong correlation exists between serum lactate and cerebral lactate concentration at the BG (r_s = 0.7, p = 0.03), Thal (r_s = 0.9 p = 0.001), and GM (r_s = 0.6, p = 0.04) regions.

Conclusion

Cerebral lactate is most significantly different between regions and severity of injury during TH. There is a moderate correlation between serum and cerebral lactate concentration measured in the deep gray nuclei during TH. Differences in injury and altered regional cerebral metabolism may account for these differences.

Secondary Increase of Lactate Levels in Asphyxiated Newborns during Hypothermia Treatment: Reflect of Suboptimal Hemodynamics (A Case Series and Review of the Literature)

Objective To evaluate whether a secondary increase of serum lactate levels in asphyxiated newborns during hypothermia treatment may reflect suboptimal dynamics. Methods-Retrospective case series and review of the literature. We present the clinical course of four asphyxiated newborns treated with hypothermia who presented with hypotension requiring inotropic support, and who displayed a secondary increase of serum lactate levels during hypothermia treatment. Serial serum lactate levels are correlated with blood pressure and inotropic support within the first 96 hours of life. Results Lactate levels initially decreased in the four patients. However, each of them started to present lower blood pressure, and lactate levels started to increase again. Inotropic support was started to raise blood pressure. The introduction of an epinephrine drip consistently worsened the increase of lactate levels in these newborns, whereas dopamine and dobutamine enabled the clearance of lactate in addition to raising the blood pressure. Rewarming was associated with hemodynamics perturbations (a decrease of blood pressure and/or an increase of lactate levels) in the three newborns who survived. Conclusions Lactate levels during the first 4 days of life should be followed as a potential marker for suboptimal hemodynamic status in term asphyxiated newborns treated with hypothermia, for whom the maintenance of homeostasis during hypothermia treatment is of utmost importance to alleviate brain injury.

The cooling tube: A novel small animal model of systemic hypothermia in awake Syrian Golden Hamsters (mesocricetus auratus)

Hypothermia is increasingly used as a therapeutic strategy in a diversity of clinical scenarios. Its impact on mammalian physiology, particularly on the microcirculatory changes of critical organ systems, are, however, incompletely understood. Close examination of the literature reveals a marked paucity of small animal models of rapid systemic hypothermia. All published models introduce important microvascular confounders by investigating either local cooling processes or using anaesthetised animals. Here we present the first rapid systemic hypothermia model in an awake hamster. We developed a waterstream cooled copper tube system for standardized systemic temperature control. With this novel system core body temperature (Tc) in 14 awake animals could be precisely stabilised at temperatures of 30°C and 18°C (7 animals, respectively) within 10-20 min. Rewarming was achieved over 10-15 min. Tolerance of the procedure was excellent. Hamsters did not show any behavioural changes in the mild hypothermia group. In the deep hypothermia group 6 of 7 animals regained normal behaviour within 2-11 hs. As hypothermia was induced in dorsal skinfold chamber bearing animals this model seems suitable for investigation of microcirculatory purposes.Advantages over previously established experimental hypothermia models are significant. Amongst these, the possibility of visualization of microcirculation, the lack of microcirculation confounding factors such as anaesthetic drugs, the ability for precise Tc control and rapid induction of hypothermia are prominent.

Hypoxic–ischemic brain injury and neuroprotection in the newborn infant

Recent clinical trials have confirmed that in term infants with moderate-to-severe hypoxic–ischemic encephalopathy, death and severe developmental disability can be reduced by early treatment with hypothermia. However, meta-analysis of these trials has confirmed that two-thirds of the survivors remain seriously impaired. The search for new neuroprotective interventions has therefore continued. Extensive research has identified the important biochemical pathways that result in neuronal loss, and the subsequent repair and regeneration processes. The most promising neuroprotective agents that limit the former, and promote the latter, are being tested in animal models of hypoxic–ischemic brain injury and are awaiting clinical trials. It is likely that a ‘cocktail’ of agents, affecting a number of pathways, will ultimately prove to be the most effective intervention. The latest additions to a long list of proposed substances are various stem cells that promote neurogenesis by releasing trophic substances into the injured brain. Future clinical trials are likely to employ early biomarkers, of which MRI and proton spectroscopy are probably the most predictive of long-term neurodevelopmental outcome. In conclusion, the exponential increase in knowledge in this field can be expected to provide many more neuroprotective agents within the next decade.

Decreased frontal lobe phosphocreatine levels in methamphetamine users

BACKGROUND

Mitochondria-related mechanisms have been suggested to mediate methamphetamine (METH) toxicity. However, changes in brain energetics associated with high-energy phosphate metabolism have not been investigated in METH users. Phosphorus-31 ((31)P) magnetic resonance spectroscopy (MRS) was used to evaluate changes in mitochondrial high energy phosphates, including phosphocreatine (PCr) and β-nucleoside triphosphate (β-NTP, primarily ATP in brain) levels. We hypothesized that METH users would have decreased high-energy PCr levels in the frontal gray matter.

METHODS

Study participants consisted of 51 METH (age=32.8±6.7) and 23 healthy comparison (age=31.1±7.5) subjects. High-energy phosphate metabolite levels were compared between the groups and potential gender differences were explored.

RESULTS

METH users had lower ratios of PCr to total pool of exchangeable phosphate (PCr/TPP) in the frontal lobe as compared to the healthy subjects (p=.001). The lower PCr levels in METH subjects were significantly associated with lifetime amount of METH use (p=.003). A sub-analysis for gender differences revealed that female METH users, who had lower daily amounts (1.1±1.0g) of METH use than males (1.4±1.7g), had significantly lower PCr/TPP ratios than male METH users, controlling for the amount of METH use (p=.02).

CONCLUSIONS

The present findings suggest that METH compromises frontal lobe high-energy phosphate metabolism in a dose-responsive manner. Our findings also suggest that the abnormality in frontal lobe high-energy phosphate metabolism might be more prominent in female than in male METH users. This is significant as decreased PCr levels have been associated with depressive symptoms, and poor responses to antidepressant treatment have been reported in those with decreased PCr levels.

The efficacy of hypothermia in hypoxic-ischemic encephalopathy at 18 mo or more

OBJECTIVE

To evaluate the efficacy of hypothermia in the treatment of hypoxic-ischemic encephalopathy (HIE) in neonates at 18 mo of age or more. Also to examine whether the severity of encephalopathy affects the efficacy of hypothermia on mortality and neurodevelopmental disability.

METHODS

The authors recruited the trials that assessed the efficacy of therapeutic hypothermia in the treatment of HIE in neonates at 18 mo of age or older up to April 2011. The meta- analysis was performed using a fixed effect model.

RESULTS

Hypothermia significantly reduced the combined rate of death or neurodevelopmental disability (RR = 0.74, 95% CI: 0.67 to 0.82; RD = -0.13, 95% CI: -0.18 to -0.08; NNT = 7, 95% CI: 6 to 9) among infants at 18 mo of age or older. Hypothermia reduced the rate of death (RR = 0.75, 95% CI: 0.64 to 0.88), neurodevelopmental disability (RR = 0.65, 95% CI: 0.54 to 0.79), cerebral palsy (RR = 0.65, 95% CI: 0.53 to 0.80), developmental delay (RR = 0.72, 95% CI: 0.57 to 0.92), neuromotor delay (RR = 0.78, 95% CI: 0.61 to 0.99) and visual deficit (RR = 0.59, 95% CI: 0.36 to 0.99). Analysis of the severity of disease showed that hypothermia reduced the combined rate of death or neurodevelopmental disability not only in moderate encephalopathy infants (RR = 0.63, 95% CI: 0.53 to 0.76) but also in severe encephalopathy infants (RR = 0.82, 95% CI: 0.74 to 0.92).

CONCLUSIONS

Hypothermia has a beneficial effect in the treatment of HIE in neonates at 18 mo of age or older.

Systemic hypothermia induced within 10 hours after birth improved neurological outcome in newborns with hypoxic-ischemic encephalopathy

OBJECTIVE

To evaluate the efficacy of systemic hypothermia when applied within 10 hours after birth to neonates with hypoxic-ischemic encephalopathy (HIE).

STUDY DESIGN

Ninety-three term infants with moderate-to-severe HIE were randomly assigned to either systemic hypothermia (n = 46) or conventional treatment (n = 47). Hypothermia was induced within 10 hours after birth, decreasing rectal temperature to 33.5°C for 72 hours, followed by slow rewarming to 36.5°C. Neurodevelopmental outcome was assessed at 18 months old. The primary outcome was death or moderate-to-severe disability.

RESULTS

Outcome data were available for 82 infants. Death or moderate-to-severe disability occurred in 21 of 44 infants (47.7%) in the control group and in 7 of 38 infants (18.4%) in the hypothermia group (P = 0.01) at 18 months. The primary outcome was not different whether hypothermia was started within 6 hours or 6 to 10 hours after birth. Subgroup analysis suggested that systemic hypothermia improved long-term outcome only in infants with moderate HIE (P = 0.009), but not in those with severe HIE. No severe hypothermia-related adverse events were observed.

CONCLUSION

Systemic hypothermia reduced the risk of disability in infants with moderate HIE, in accordance with earlier studies. Hypothermia was induced within 6 hours in most infants, but delaying the onset to 6 to 10 hours after birth did not negatively affect primary outcome. Further studies with a large number of patients are needed to confirm that delayed cooling is equally effective.

Safety and efficacy of topiramate in neonates with hypoxic ischemic encephalopathy treated with hypothermia (NeoNATI)

BACKGROUND

Despite progresses in neonatal care, the mortality and the incidence of neuro-motor disability after perinatal asphyxia have failed to show substantial improvements. In countries with a high level of perinatal care, the incidence of asphyxia responsible for moderate or severe encephalopathy is still 2-3 per 1000 term newborns. Recent trials have demonstrated that moderate hypothermia, started within 6 hours after birth and protracted for 72 hours, can significantly improve survival and reduce neurologic impairment in neonates with hypoxic-ischemic encephalopathy. It is not currently known whether neuroprotective drugs can further improve the beneficial effects of hypothermia. Topiramate has been proven to reduce brain injury in animal models of neonatal hypoxic ischemic encephalopathy. However, the association of mild hypothermia and topiramate treatment has never been studied in human newborns. The objective of this research project is to evaluate, through a multicenter randomized controlled trial, whether the efficacy of moderate hypothermia can be increased by concomitant topiramate treatment.

METHODS/DESIGN

Term newborns (gestational age ≥ 36 weeks and birth weight ≥ 1800 g) with precocious metabolic, clinical and electroencephalographic (EEG) signs of hypoxic-ischemic encephalopathy will be randomized, according to their EEG pattern, to receive topiramate added to standard treatment with moderate hypothermia or standard treatment alone. Topiramate will be administered at 10 mg/kg once a day for the first 3 days of life. Topiramate concentrations will be measured on serial dried blood spots. 64 participants will be recruited in the study. To evaluate the safety of topiramate administration, cardiac and respiratory parameters will be continuously monitored. Blood samplings will be performed to check renal, liver and metabolic balance. To evaluate the efficacy of topiramate, the neurologic outcome of enrolled newborns will be evaluated by serial neurologic and neuroradiologic examinations. Visual function will be evaluated by means of behavioural standardized tests.

DISCUSSION

This pilot study will explore the possible therapeutic role of topiramate in combination with moderate hypothermia. Any favourable results of this research might open new perspectives about the reduction of cerebral damage in asphyxiated newborns.

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.

Post-stroke hypothermia provides neuroprotection through inhibition of AMP-activated protein kinase

Hypothermia is robustly protective in pre-clinical models of both global and focal ischemia, as well as in patients after cardiac arrest. Although the mechanism for hypothermic neuroprotection remains unknown, reducing metabolic drive may play a role. Capitalizing on the beneficial effects of hypothermia while avoiding detrimental effects such as infection will be the key to moving this therapy forward as a treatment for stroke. AMPK is a master energy sensor that monitors levels of key energy metabolites. AMPK is activated via phosphorylation (pAMPK) when cellular energy levels are low, such as that seen during ischemia. AMPK activation appears to be detrimental in experimental stroke, likely via exacerbating ischemia-induced metabolic failure. We tested the hypothesis that hypothermia reduces AMPK activation. First, it was found that hypothermia reduced infarct after middle cerebral artery occlusion. Second, induced hypothermia reduced brain pAMPK in both sham control and stroke mice. Third, hypothermic neuroprotection was ameliorated after administration of compound C, an AMPK inhibitor. Finally, deletion of one of the catalytic isoforms of AMPK completely reversed the effect of hypothermia on stroke outcome after both acute and chronic survival. These effects were mediated by a reduction in AMPK activation rather than a reduction in LKB1, an upstream AMPK kinase. In summary, these studies provide evidence that hypothermia exerts its protective effect in part by inhibiting AMPK activation in experimental focal stroke. This suggests that AMPK represents a potentially important biological target for stroke treatment.

Temperature management in acute neurologic injury: to cool or not to cool

Therapeutic hypothermia is becoming an important intervention following acute neurologic injury despite inconclusive results concerning efficacy. This enthusiasm primarily stems from a lack of other effective interventions in this population. With the increase in the use of therapeutic hypothermia, several practical issues must be considered when initiating this intervention. Clinical pharmacists can play an important role in anticipating and addressing some complications such as shivering, slow drug metabolism, and infection. This review will discuss the available literature concerning the efficacy of therapeutic hypothermia in various neurologic injuries, as well as the most common adverse events associated with it.

Effects of selective head cooling on cerebral blood flow and metabolism in newborn piglets after hypoxia-ischemia

AIM

the effect of selective head cooling on cerebral blood flow (CBF) and cerebral metabolism rate (CMR) was investigated in newborn piglets.

METHODS

seven days old newborn piglets were randomly assigned to one of the following three groups: Selective head cooling in normal piglets (n=4), selective head cooling after HI (n=6) and normal temperature after HI (n=6). CBF was measured with color microspheres. Cerebral oxygenation metabolism rate (CMRO(2)), Cerebral glucose consumption (CMR(Glu)) and Cerebral lactate production (CMR(lac)) were calculated.

RESULT

in normal piglets, CBF, CMRO(2) and CMR(glu) were significantly decreased at both 35°C (P<0.05) and 32°C (P<0.01), while CMR(lac) did not change. Compared to baseline, CBF and CMRO(2) were significantly reduced (P<0.05), while CMR(glu) and CMR(lac) were significantly increased (P<0.01), AVDO(2) was decreased (P<0.05), while AVD(glu) and AVD(lac) were significantly increased (P<0.01 respectively) in HI piglets with normal temperature respectively. Compared to normal temperature after HI, selective head cooling after HI significantly reduced CMR(glu) and CMR(lac), and AVDO(2), AVD(glu), AVD(lac) were improved at 35°C.

CONCLUSION

selective head cooling not only reduced energy consumption, but also improve brain oxygen metabolism in newborn after HI.

Perinatal hypoxic-ischemic encephalopathy

Perinatal hypoxic-ischemic encephalopathy (HIE) is an important cause of brain injury in the newborn and can result in long-term devastating consequences. Perinatal hypoxia is a vital cause of long-term neurologic complications varying from mild behavioural deficits to severe seizure, mental retardation, and/or cerebral palsy in the newborn. In the mammalian developing brain, ongoing research into pathophysiological mechanism of neuronal injury and therapeutic strategy after perinatal hypoxia is still limited. With the advent of promising therapy of hypothermia in HIE, this paper reviews the pathophysiology of HIE and the future potential neuroprotective strategies for clinical potential for hypoxia sufferers.

Resuscitation of newborn piglets. short-term influence of FiO2 on matrix metalloproteinases, caspase-3 and BDNF

BACKGROUND

Perinatal hypoxia-ischemia is a major cause of mortality and cerebral morbidity, and using oxygen during newborn resuscitation may further harm the brain. The aim was to examine how supplementary oxygen used for newborn resuscitation would influence early brain tissue injury, cell death and repair processes and the regulation of genes related to apoptosis, neurodegeneration and neuroprotection.

METHODS AND FINDINGS

Anesthetized newborn piglets were subjected to global hypoxia and then randomly assigned to resuscitation with 21%, 40% or 100% O(2) for 30 min and followed for 9 h. An additional group received 100% O(2) for 30 min without preceding hypoxia. The left hemisphere was used for histopathology and immunohistochemistry and the right hemisphere was used for in situ zymography in the corpus striatum; gene expression and the activity of various relevant biofactors were measured in the frontal cortex. There was an increase in the net matrix metalloproteinase gelatinolytic activity in the corpus striatum from piglets resuscitated with 100% oxygen vs. 21%. Hematoxylin-eosin (HE) staining revealed no significant changes. Nine hours after oxygen-assisted resuscitation, caspase-3 expression and activity was increased by 30-40% in the 100% O(2) group (n = 9/10) vs. the 21% O(2) group (n = 10; p<0.04), whereas brain-derived neurotrophic factor (BDNF) activity was decreased by 65% p<0.03.

CONCLUSIONS

The use of 100% oxygen for resuscitation resulted in increased potentially harmful proteolytic activities and attenuated BDNF activity when compared with 21%. Although there were no significant changes in short term cell loss, hyperoxia seems to cause an early imbalance between neuroprotective and neurotoxic mechanisms that might compromise the final pathological outcome.

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.

Long-term neuroprotective effect of postischemic hypothermia in a neonatal rat model of severe hypoxic ischemic encephalopathy: a comparative study on the duration and depth of hypothermia

It is not known whether deeper or longer hypothermia (HT) can achieve better neuroprotection against hypoxic ischemic encephalopathy (HIE) in neonates. To compare the neuroprotective effects of different durations and temperatures of postischemic HT in neonatal rats with severe HIE, 7-d-old rats were subjected to the Rice-Vannucci model for 150 min hypoxia. Only the rats with identified brain lesions in diffusion-weighted MRI were assigned to normothermia (NT, 36° C/48 h) or four HT (HT-30° C/48 h; HT-30° C/24 h; HT-33° C/48 h; and HT-33° C/24 h) groups. H-magnetic resonance spectroscopy (H-MRS) and T2-weighted MRI were obtained serially, and functional studies were performed. HT groups showed significantly greater residual hemispheric volume and better rotarod and cylinder tests than did the NT group at 5 wk postischemia. HT groups also showed lower lactate-plus-lipid level in H-MRS than did the NT group at 7 d postischemia. All of these outcome variables, however, did not differ among the 4 HT subgroups, despite a trend toward greater residual brain volume in the 48-h HT versus 24-h HT subgroups. In conclusion, neither reducing the target temperature from 33 to 30° C nor prolonging the duration from 24 to 48 h produced further improvements in neurologic outcomes in neonatal rat with HIE.

Patterns of neonatal hypoxic-ischaemic brain injury

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

Therapeutic hypothermia for neonatal hypoxic ischaemic encephalopathy

There is now a strong evidence base supporting therapeutic hypothermia for infants with moderate or severe neonatal hypoxic ischaemic encephalopathy. Experimental and clinical data indicate that induced hypothermia reduces cerebral hypoxic ischaemic injury and randomized clinical trials in newborns with hypoxic ischaemic encephalopathy confirm improved neurological outcomes and survival at 18 months of age with therapeutic hypothermia. Studies are on-going to confirm whether these benefits are maintained in later childhood. Efforts are now focused on optimal implementation of therapeutic hypothermia in clinical practice: training in the assessment of severity of encephalopathy; initiation and maintenance of hypothermia before admission to a cooling facility; care of the infant during cooling; and appropriate investigation and follow-up are crucial for optimizing neurological outcomes. The establishment of registries of infants with hypoxic ischaemic encephalopathy and audit are important for guiding clinical practice.

Patterns of neonatal hypoxic-ischaemic brain injury

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

Advanced neuroimaging techniques: their role in the development of future fetal and neonatal neuroprotection

Injury to the developing brain is associated with significant risk for potential lifelong, and wide-ranging neurodevelopmental consequences. Despite major advances in neonatal intensive care in recent decades, truly informed brain-oriented care of the critically ill neonate remains lacking. Consequently, this has hindered the development of preventive neuroprotective interventions, which is in large part due to the inherent difficulties in diagnosis, timing, and the severity of insults. Recent advances in understanding the cellular mechanisms of neonatal brain injury, together with the successful application of cutting-edge neuroimaging techniques, have markedly improved our understanding of the timing and evolution of structural injury to the immature brain, and its functional consequences. Triggered by these important advances, there is intense and renewed interest in the development of brain-oriented therapies, including neuroprotective strategies aimed at circumventing the injurious effects of neonatal brain insults. This article will provide an overview of normal and abnormal brain development, and explore the role of advanced neuroimaging techniques in neuroprotective therapies in the neonatal intensive care unit.

Hypothermia as a cytoprotective strategy in ischemic tissue injury

Hypothermia is a well established cytoprotectant, with remarkable and consistent effects demonstrated across multiple laboratories. At the clinical level, it has recently been shown to improve neurological outcome following cardiac arrest and neonatal hypoxia-ischemia. It is increasingly being embraced by the medical community, and could be considered an effective neuroprotectant. Conditions such as brain injury, hepatic encephalopathy and cardiopulmonary bypass seem to benefit from this intervention. It's role in direct myocardial protection is also being explored. A review of the literature has demonstrated that in order to appreciate the maximum benefits of hypothermia, cooling needs to begin soon after the insult, and maintained for relatively long period periods of time. In the case of ischemic stroke, cooling should ideally be applied in conjunction with the re-establishment of cerebral perfusion. Translating this to the clinical arena can be challenging, given the technical challenges of rapidly and stably cooling patients. This review will discuss the application of hypothermia especially as it pertains to its effects neurological outcome, cooling methods, and important parameters in optimizing hypothermic protection.

Moderate hypothermia to treat perinatal asphyxial encephalopathy

BACKGROUND

Whether hypothermic therapy improves neurodevelopmental outcomes in newborn infants with asphyxial encephalopathy is uncertain.

METHODS

We performed a randomized trial of infants who were less than 6 hours of age and had a gestational age of at least 36 weeks and perinatal asphyxial encephalopathy. We compared intensive care plus cooling of the body to 33.5 degrees C for 72 hours and intensive care alone. The primary outcome was death or severe disability at 18 months of age. Prespecified secondary outcomes included 12 neurologic outcomes and 14 other adverse outcomes.

RESULTS

Of 325 infants enrolled, 163 underwent intensive care with cooling, and 162 underwent intensive care alone. In the cooled group, 42 infants died and 32 survived but had severe neurodevelopmental disability, whereas in the noncooled group, 44 infants died and 42 had severe disability (relative risk for either outcome, 0.86; 95% confidence interval [CI], 0.68 to 1.07; P=0.17). Infants in the cooled group had an increased rate of survival without neurologic abnormality (relative risk, 1.57; 95% CI, 1.16 to 2.12; P=0.003). Among survivors, cooling resulted in reduced risks of cerebral palsy (relative risk, 0.67; 95% CI, 0.47 to 0.96; P=0.03) and improved scores on the Mental Developmental Index and Psychomotor Developmental Index of the Bayley Scales of Infant Development II (P=0.03 for each) and the Gross Motor Function Classification System (P=0.01). Improvements in other neurologic outcomes in the cooled group were not significant. Adverse events were mostly minor and not associated with cooling.

CONCLUSIONS

Induction of moderate hypothermia for 72 hours in infants who had perinatal asphyxia did not significantly reduce the combined rate of death or severe disability but resulted in improved neurologic outcomes in survivors. (Current Controlled Trials number, ISRCTN89547571.)

Mechanisms of action, physiological effects, and complications of hypothermia

BACKGROUND

Mild to moderate hypothermia (32-35 degrees C) is the first treatment with proven efficacy for postischemic neurological injury. In recent years important insights have been gained into the mechanisms underlying hypothermia's protective effects; in addition, physiological and pathophysiological changes associated with cooling have become better understood.

OBJECTIVE

To discuss hypothermia's mechanisms of action, to review (patho)physiological changes associated with cooling, and to discuss potential side effects.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

A myriad of destructive processes unfold in injured tissue following ischemia-reperfusion. These include excitotoxicty, neuroinflammation, apoptosis, free radical production, seizure activity, blood-brain barrier disruption, blood vessel leakage, cerebral thermopooling, and numerous others. The severity of this destructive cascade determines whether injured cells will survive or die. Hypothermia can inhibit or mitigate all of these mechanisms, while stimulating protective systems such as early gene activation. Hypothermia is also effective in mitigating intracranial hypertension and reducing brain edema. Side effects include immunosuppression with increased infection risk, cold diuresis and hypovolemia, electrolyte disorders, insulin resistance, impaired drug clearance, and mild coagulopathy. Targeted interventions are required to effectively manage these side effects. Hypothermia does not decrease myocardial contractility or induce hypotension if hypovolemia is corrected, and preliminary evidence suggests that it can be safely used in patients with cardiac shock. Cardiac output will decrease due to hypothermia-induced bradycardia, but given that metabolic rate also decreases the balance between supply and demand, is usually maintained or improved. In contrast to deep hypothermia (<or=30 degrees C), moderate hypothermia does not induce arrhythmias; indeed, the evidence suggests that arrhythmias can be prevented and/or more easily treated under hypothermic conditions.

CONCLUSIONS

Therapeutic hypothermia is a highly promising treatment, but the potential side effects need to be properly managed particularly if prolonged treatment periods are required. Understanding the underlying mechanisms, awareness of physiological changes associated with cooling, and prevention of potential side effects are all key factors for its effective clinical usage.

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

Hypothermia

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

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.

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.

Cerebral oxygenation and electrical activity after birth asphyxia: their relation to outcome

OBJECTIVE

To determine the value of regional cerebral oxygen saturation (rSo2), fractional cerebral tissue oxygen extraction (FTOE) measured by near-infrared spectroscopy (NIRS), and amplitude integrated electroencephalogram (aEEG) after birth asphyxia in relation to neurodevelopmental outcome.

METHODS

NIRS measured rSo2, FTOE, and aEEG were monitored simultaneously, together with arterial oxygen saturation (Sao2) and blood pressure during the first 48 hours after severe birth asphyxia in 18 term infants. FTOE was calculated as [Sao2-rSo2]/Sao2. Neurodevelopmental outcome was assessed at 3, 9, and 18 months and 3 and 5 years of age. At the time points 6, 12, 18, 24, 30, 36, 42, and 48 hours after birth, the mean values of Sao2, rSo2, FTOE, and mean arterial blood pressure were calculated over a 1-hour period. A stepwise-regression model was used to investigate the relative contribution of rSo2, FTOE, or aEEG to developmental outcome.

RESULTS

Nine Infants died during the neonatal period as a result of neurologic deterioration, and 8 infants had a normal outcome at 5 years of age. One child developed learning disabilities and a mild diplegia. The rSo2 and FTOE remained stable in infants with a normal outcome. The rSo2 increased and the FTOE decreased after 24 hours in the infants with an adverse outcome. (rSo2: 65% vs 84% at 12 and 48 hours, respectively; FTOE: 0.32 vs 0.12 at 12 and 48 hours, respectively). aEEG showed the closest relationship with outcome, but also rSo2 showed a significant correlation 24 hours after birth.

CONCLUSIONS

rSo2 and FTOE seem to reflect secondary energy failure. aEEG showed the closest relationship with outcome after severe birth asphyxia.

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.

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.

Effects of rapid rewarming on cerebral nitric oxide production and cerebral hemodynamics after hypothermia therapy for kainic acid-induced seizures in immature rabbits

BACKGROUND

The aim of the present study was to investigate whether rapid rewarming after hypothermia therapy during seizures alters the endogenous nitric oxide (NO) production in and around hippocampus, cortical cerebral blood flow (cCBF), and mean arterial blood pressure (MABP) in immature rabbits.

METHODS

The hypothermic rabbits (rectal temperatures, 33 degrees C) were given kainic acid (KA; 12 mg/kg, i.v; at 0 min), followed by cooling (33 degrees C) for 60 min (at 60 min), then either rewarming (RW; 33-37 degrees C) was started (KA[+]RW[+] group, n = 7) or cooling was continued (KA[+]RW[-] group, n = 7) for another 60 min (at the end 120 min). In the KA(-)RW(+) group (n = 5), 0.5 mL normal saline was given (at time 0 min), followed by cooling (33 degrees C) for 60 min (at 60 min), then rewarming to 37 degrees C was started with observation for another 60 min (at the end 120 min). NO production in and around hippocampus was continuously measured by an NO-selective electrode, cCBF by laser Doppler flowmetry, cortical electroencephalogram (EEG), rectal and cerebral temperatures, and MABP during the experiment. Comparisons were made of these parameters between the values at 60 min and 120 min after the KA administrations.

RESULTS

KA administration induced abnormal discharges in both KA(+)RW(+) and KA(+)RW(-) groups at the same degree. The KA(+)RW(+) group had a significant increase in %NO, and significant decreases in %cCBF and MABP after rapid rewarming, compared with before rewarming. In the KA(+)RW(-) group, there were no significant changes in %NO, %cCBF, and MABP between values at 60 and 120 min. These changes after rapid rewarming in the KA(+)RW(+) group were different from those with only elevation in brain temperature from 33 to 37 degrees C without seizures (KA[-]RW[+] group).

CONCLUSIONS

These results suggest that rapid rewarming after hypothermia therapy induces an increase in the NO production in and around hippocampus and the decreases in cCBF and MABP during seizures in immature rabbits.

Traumatic injury in the developing brain–effects of hypothermia

Little is known about the underlying mechanisms of head trauma in the developing brains, despite considerable social and economic impact following such injuries. Age has been shown to substantially influence morbidity and mortality. Children younger than 4 years of age had worse cognitive, motor, and brain atrophy outcomes than children 6 years of age and older. Younger children tend to more frequently suffer from diffuse cerebral swelling compared to adults. Typical autoptic findings also include axonal injury and ischemic neurodegeneration. These differences impact not only the primary response of the brain to injury but the secondary response as well. The complexity of damaging mechanisms in traumatic brain injury contributes to the problem of determining effective therapy. As an alternative/ adjunct to pharmacological approaches, hypothermia has been shown to be cerebroprotective in traumatized adult brains. Although a large number of animal studies have shown protective effects of hypothermia in a variety of damaging mechanisms after TBI, little data exist for young, developing brains. The injury mechanisms of TBI in the immature, effects of hypothermia following resuscitation on adult and immature traumatized brains, and some possible mechanisms of action of hypothermia in the immature traumatized brain are discussed in this review.

Hypothermia during kainic acid-induced seizures reduces hippocampal lesions and cerebral nitric oxide production in immature rabbits

We investigated (1) whether cerebral hypothermia during kainic acid (KA)-induced seizures was neuroprotective; and (2) whether nitric oxide (NO) production in the brain during seizures was altered by cerebral hypothermia in immature rabbits. Twelve female rabbits, aged 2 weeks, were anesthetized, paralyzed and mechanically ventilated. We continuously measured NO production in the brain by NO-selective electrode, cortical electroencephalogram (EEG), regional cerebral blood flow (rCBF) by laser Doppler flowmetry, rectal and cerebral temperatures and mean arterial blood pressure (MABP) during KA (12 mg/kg, i.v.)-induced seizures in the hypothermic group (n = 6; rectal temperature, 33 degrees C), and in the normothermic group (n = 6; rectal temperature, 37 degrees C). The normothermic group showed a gradual increase in NO generation in the brain, which was significantly inhibited in the hypothermic group. There were no significant differences in the increases in rCBF, MABP, arterial blood gases, blood glucose, or EEG abnormalities between the two groups. Neuronal damages in the hippocampus (CA3) were significantly lower in hypothermia than in normothermia. These results suggest that hypothermia attenuates NO production during drug-induced seizures and decreases hippocampal brain lesions in the immature rabbit brain. These results may help to explain the neuroprotective effects of hypothermia.

Relationship between cerebral interstitial levels of amino acids and phosphorylation potential during secondary energy failure in hypoxic-ischemic newborn piglets

The aim of this study was to determine the validity of the hypothesis that excitatory amino acids are related to phosphorylation potential during primary and secondary cerebral energy failure observed in asphyxiated infants. We report here the results of experiments using newborn piglets subjected to severe transient cerebral hypoxia-ischemia followed by resuscitation. We examined cerebral energy metabolism by phosphorus nuclear magnetic resonance spectroscopy and changes in levels of amino acid neurotransmitters in the cortex by microdialysis before, during, and up to 24 h after the hypoxic-ischemic insult. The concentrations of aspartate, glutamate, taurine, and gamma-aminobutyric acid were significantly elevated during the hypoxic-ischemic insult compared with prebaseline values. Shortly after resuscitation, glutamate, taurine, and gamma-aminobutyric acid concentrations decreased but then began to increase again. These secondary elevations were greater than the primary elevations. A negative linear correlation was found between primary interstitial levels of glutamate and taurine and minimum values of phosphocreatine/inorganic phosphate during the secondary energy failure. The cerebral energy state depended on the time course of changes in excitatory amino acids, suggesting that amino acids play distinct roles during the early and delayed phases of injury.

Early head cooling in newborn piglets is neuroprotective even in the absence of profound systemic hypothermia

BACKGROUND

Selective head cooling in the newborn infant has been proposed as a neuroprotective treatment with a lower level of systemic adverse effect than that of systemic hypothermia. However, the efficacy is not confirmed as well as that of systemic hypothermia. In order to analyze the safety and efficacy of selective head cooling, 25 newborn piglets were randomly selected for either normothermic or hypothermic treatment.

METHODS

Global hypoxic insult was induced by lowering the oxygen concentration to the maximal level to maintain the background electroencephalogram (EEG) voltage under 7 microV for 45 min. The core temperature of normothermic piglets was maintained between 38.5 degrees C and 39 degrees C, while prophylactic cooling was applied to the hypothermic piglets at the same time of the insult. Very mild systemic hypothermia by 1 degrees C was induced in addition to selective head cooling with 10 degrees C coolant temperature. Animals were killed for histopathological examination seven hours after the end of the insult.

RESULTS

Two normothermic piglets died while all hypothermic piglets survived. Neuropathological findings were significantly severer in the normothermic group than in the hypothermic group. Intracranial pressure was significantly lower, and EEG recovery was significantly better in the hypothermic piglets. There was no significant difference in the lowest oxygen concentration, degrees of acidosis, blood lactate, and blood pressure between the groups, although heart rate was significantly lower in the hypothermic group.

CONCLUSIONS

We have demonstrated that early head cooling was effective in preventing some of the earliest brain damage due to hypoxic insult even in the absence of profound systemic hypothermia.

Effects of hypothermia on energy metabolism in Mammalian central nervous system

This review analyzes, in some depth, results of studies on the effect of lowered temperatures on cerebral energy metabolism in animals under normal conditions and in some selected pathologic situations. In sedated and paralyzed mammals, acute uncomplicated 0.5- to 3-h hypothermia decreases the global cerebral metabolic rate for glucose (CMR(glc)) and oxygen (CMRo(2)) but maintains a slightly better energy level, which indicates that ATP breakdown is reduced more than its synthesis. Intracellular alkalinization stimulates glycolysis and independently enhances energy generation. Lowering of temperature during hypoxia-ischemia slows the rate of glucose, phosphocreatine, and ATP breakdown and lactate and inorganic phosphate formation, and improves recovery of energetic parameters during reperfusion. Mild hypothermia of 12 to 24-h duration after normothermic hypoxic-ischemic insults seems to prevent or ameliorate secondary failures in energy parameters. The authors conclude that lowered head temperatures help to protect and maintain normal CNS function by preserving brain ATP supply and level. Hypothermia may thus prove a promising avenue in the treatment of stroke and trauma and, in particular, of perinatal brain injury.

Advances in postnatal neuroimaging: relevance to pathogenesis and treatment of brain injury

The human brain is susceptible to a wide variety of insults. The permanent residua of these abnormalities are represented in dysfunction of one or more areas of neurodevelopment. A full understanding of normal brain development, mechanisms of brain injury, and consequences for subsequent brain development is required to determine which infants are at risk for neurodevelopmental handicap, and to monitor the effects of new treatments and management regimens designed to prevent these disabilities. Advanced magnetic resonance techniques, such as quantitative morphometric magnetic resonance techniques, diffusion-weighted magnetic resonance techniques, and magnetic resonance spectroscopy applied to the study of early human brain development have given us a better understanding of the pathophysiologic mechanisms of brain injury and its effects on subsequent brain development. Magnetic resonance imaging has provided an invaluable tool for the study of the fetal and newborn brain in vivo.

Delayed hypothermia prevents decreases in N-acetylaspartate and reduced glutathione in the cerebral cortex of the neonatal pig following transient hypoxia-ischaemia

The effects of normothermia and delayed hypothermia on the levels of N-acetylaspartate (NAA), reduced glutathione (GSH) and the activities of mitochondrial complex I, II-III, IV and citrate synthase were measured in brain homogenates obtained from anaesthetized neonatal pigs following transient in vivo hypoxia-ischaemia. In the normothermic animals there was a significant decrease in complex I activity and in the levels of GSH and NAA when compared to the controls. Delayed hypothermia preserved NAA and GSH at control levels and enhanced the rate of complex II-III activity. There was correlation (R = 0.79) between GSH and NAA levels when data from all three experimental groups were analyzed. Citrate synthase activity was not significantly different in the three groups, indicating maintenance of mitochondrial integrity. These data suggest that delayed hypothermia affords protection of integrated mitochondrial function in the neonatal brain following transient hypoxia-ischaemia.

Delayed postischemic hypothermia improves long-term behavioral outcome after cerebral hypoxia-ischemia in neonatal rats

Hypothermia may be an ideal neuroprotective intervention in hypoxic-ischemic encephalopathy after perinatal asphyxia. The present study describes the long-term effects of prolonged resuscitative whole-body hypothermia initiated 2 h after hypoxic-ischemic injury on brain morphology and neuropsychological behavior in 7-d-old rats. After right common carotid artery ligation and exposure to hypoxia of 8% O(2) for 105 min, 10 animals were kept normothermic at 37 degrees C and 10 animals were cooled to 30 degrees C rectal temperature for 26 h, starting 2 h after the hypoxic-ischemic insult. All hypoxic-ischemic animals were gavage fed to guarantee long-term survival. Neuroprotection was evaluated by magnetic resonance imaging and behavioral testing. Hypothermia significantly reduced the final size of cerebral infarction by 23% at 6 wk after the insult. The most extended tissue rescue was found in the hippocampus (21%, p = 0.031), followed by the striatum (13%, p = 0.143) and the cortex (11%, p = 0.160). Cooling salvaged spatial memory deficits verified at 5 wk of recovery with Morris Water Maze test; whereas circling abnormalities after apomorphine injection and sensory motor dysfunctions on rotating treadmill improved, yet did not reach statistical significance. When compared with controls, hypoxic-ischemic animals performed worse in all behavioral tests. Hypothermia did not influence functional outcome in controls. Significant correlations between behavioral performance and corresponding regional brain volumes were found. We conclude that 26 h of mild to moderate resuscitative hypothermia leads not only to brain tissue rescue, but most important to long-lasting behavioral improvement throughout brain maturation despite severity of injury and delayed onset of cooling.

Early increases in brain myo-inositol measured by proton magnetic resonance spectroscopy in term infants with neonatal encephalopathy

Our aim was to assess brain myo-inositol/creatine plus phosphocreatine (Cr) in the first week in term infants with neonatal encephalopathy using localized short echo time proton magnetic resonance spectroscopy and to relate this to measures of brain injury, specifically lactate/Cr in the first week, basal ganglia changes on magnetic resonance imaging (MRI), and neurodevelopmental outcome at 1 y. Fourteen term infants with neonatal encephalopathy of gestational age (mean +/- SD) 39.6 +/- 1.6 wk, birth weight 3270 +/- 490 g, underwent MRI and magnetic resonance spectroscopy at 3.5 +/- 2.1 d. Five infants were entered in a pilot study of treatment with moderate whole-body hypothermia for neonatal encephalopathy; two were being cooled at the time of the scan. T(1)- and T(2)-weighted transverse magnetic resonance images were graded as normal or abnormal according to the presence or absence of the normal signal intensity of the posterior limb of the internal capsule and signal intensity changes in the basal ganglia. Localized proton magnetic resonance spectroscopy data were obtained from an 8-cm(3) voxel in the basal ganglia using echo times of 40 and 270 ms, and the peak area ratios of myo-inositol/Cr and lactate/Cr were measured. Outcome was scored using Griffith's development scales and neurodevelopmental examination at 1 y. MRI and outcome were normal in six infants and abnormal in eight. myo-Inositol/Cr and lactate/Cr were higher in infants with abnormal MRI and outcome (p < 0.01, p < 0.01, respectively). myo-Inositol/Cr and lactate/Cr were correlated (p < 0.01) and were both correlated to the Griffith's developmental scales (p < 0.01, p < 0.01, respectively). In conclusion, these preliminary data suggest that early increases in brain basal ganglia myo-inositol/Cr in infants with neonatal encephalopathy are associated with increased lactate/Cr, MRI changes of severe injury, and a poor neurodevelopmental outcome at 1 y.

An improved survival model of hypoxia/ischaemia in the piglet suitable for neuroprotection studies

The purpose of this study was to develop a newborn piglet model of hypoxia/ischaemia which would better emulate the clinical situation in the asphyxiated human neonate and produce a consistent degree of histopathological injury following the insult. One-day-old piglets (n=18) were anaesthetised with a mixture of propofol (10 mg/kg/h) and alfentinal (55.5 microg/kg/h) i.v. The piglets were intubated and ventilated. Physiological variables were monitored continuously. Hypoxia was induced by decreasing the inspired oxygen (FiO(2)) to 3-4% and adjusting FiO(2) to maintain the cerebral function monitor peak amplitude at < or =5 microV. The duration of the mild insult was 20 min while the severe insult was 30 min which included 10 min where the blood pressure was allowed to fall below 70% of baseline. Control piglets (n=4 of 18) were subjected to the same protocol except for the hypoxic/ischaemic insult. The piglets were allowed to recover from anaesthesia then euthanased 72 h after the insult. The brains were perfusion-fixed, removed and embedded in paraffin. Coronal sections were stained by haematoxylin/eosin. A blinded observer examined the frontal and parietal cortex, hippocampus, basal ganglia, thalamus and cerebellum for the degree of damage. The total mean histology score for the five areas of the brain for the severe insult was 15.6+/-4.4 (mean +/-S.D., n=7), whereas no damage was seen in either the mild insult (n=4) or control groups. This 'severe damage' model produces a consistent level of damage and will prove useful for examining potential neuroprotective therapies in the neonatal brain.

Cerebral metabolism and regional cerebral blood flow during moderate systemic cooling in newborn piglets

BACKGROUND

Clinical trials of hypothermic therapy in asphyxiated infants have started recently. However, clinical studies have been delayed by the difficulty in selecting infants with a bad neurological prognosis and by the concern regarding adverse effects of hypothermia. The purpose of this study is to examine the effects of systemic cooling on cerebral metabolism (CMR) and the regional cerebral blood flow (rCBF) in newborn piglets.

METHODS

The rCBF in the seven parts of the brain were measured with colored microspheres. The blood samples for the measurement of cerebral oxygen consumption (CMRO2) and cerebral glucose consumption (CMRglc) was collected from the umbilical artery and the superior sagittal sinus.

RESULTS

Reductions of cerebral cortex temperature to 32 degrees C decreased blood flow in all brain regions. In particular, blood flow in the brainstem decreased more significantly than in any other region. The total cerebral blood flow (CBF), CMRO2 and CMRglc, respectively, decreased to 32.3+/-3.9 mL/100 g per min, 2.8+/-1.0 mLO2/100 g per min and 22+/-12 mmol/100 g per min at 32 degrees C (41, 53 and 46% of the initial value). The CBF decreased in parallel with CMRO2 and CMRglc down to 35 degrees C, but CBF decreased to a greater extent than CMRO2 and CMRglc at below 35 degrees C.

CONCLUSIONS

The indication of hypothermic therapy and the degree of cooling have to be performed very carefully. Systemic cooling is especially dangerous for the total asphyxiated infants who might have damage to the brainstem because the blood flow in the brainstem has significantly decreased during hypothermia.