Neuroprotective Effect Of Therapeutic Hypothermia Research Articles

The Neuroprotective Effect of Therapeutic Hypothermia in Cognitive Impairment of an Ischemia/Reperfusion Injury Mouse Model.

Background and Objectives: Therapeutic hypothermia (TH) shows promise as an approach with neuroprotective effects, capable of reducing secondary brain damage and intracranial pressure following successful mechanical thrombectomy in the acute phase. However, its effect on cognitive impairment remains unclear. This study investigated whether TH can improve cognitive impairment in a mouse model of transient middle cerebral artery occlusion followed by reperfusion (tMCAO/R). Materials and Methods: Nine-week-old C57BL/6N mice (male) were randomly assigned to three groups: sham, tMCAO/R, and tMCAO/R with TH. Cognitive function was assessed 1 month after model induction using the Y-maze test, and regional cerebral glucose metabolism was measured through positron emission tomography with fluorine-18 fluorodeoxyglucose. Results: tMCAO/R induced cognitive impairment, which showed improvement with TH. The TH group exhibited a significant recovery in cerebral glucose metabolism in the thalamus compared to the tMCAO/R group. Conclusions: These findings indicate that TH may hold promise as a therapeutic strategy for alleviating ischemia/reperfusion-induced cognitive impairment.

Hypothermia Attenuates Neurotoxic Microglial Activation via TRPV4.

Therapeutic hypothermia (TH) provides neuroprotection. However, the cellular mechanisms underlying the neuroprotective effects of TH are not fully elucidated. Regulation of microglial activation has the potential to treat a variety of nervous system diseases. Transient receptor potential vanilloid 4 (TRPV4), a nonselective cation channel, is activated by temperature stimulus at 27-35°C. Although it is speculated that TRPV4 is associated with the neuroprotective mechanisms of TH, the role of TRPV4 in the neuroprotective effects of TH is not well understood. In the present study, we investigated whether hypothermia attenuates microglial activation via TRPV4 channels. Cultured microglia were incubated under normothermic (37°C) or hypothermic (33.5°C) conditions following lipopolysaccharide (LPS) stimulation. Hypothermic conditions suppressed the expression of pro-inflammatory cytokines, inducible nitric oxide synthase, and the number of phagocytic microglia. AMP-activated protein kinase (AMPK)-NF-κB signaling was inhibited under hypothermic conditions. Furthermore, hypothermia reduced neuronal damage induced by LPS-treated microglial cells. Treatment with TRPV4 antagonist in normothermic culture replicated the suppressive effects of hypothermia on microglial activation and microglia-induced neuronal damage. In contrast, treatment with a TRPV4 agonist in hypothermic culture reversed the suppressive effect of hypothermia. These findings suggest that TH suppresses microglial activation and microglia-induced neuronal damage via the TRPV4-AMPK-NF-κB pathway. Although more validation is needed to consider differences according to age, sex, and specific central nervous system regions, our findings may offer a novel therapeutic approach to complement TH.

No neuroprotective effect of therapeutic hypothermia following lipopolysaccharide-sensitized hypoxia-ischemia: a newborn piglet study

IntroductionTherapeutic hypothermia is the only proven neuroprotective treatment for hypoxic-ischemic encephalopathy. However, studies have questioned whether therapeutic hypothermia may benefit newborns subjected to infection or inflammation before a hypoxic-ischemic insult. We aimed to compare newborn piglets with lipopolysaccharide-sensitized hypoxia-ischemia treated with and without therapeutic hypothermia with regards to measures of neuroprotection.MethodsA total of 32 male and female piglets were included in this randomized experimental study. Lipopolysaccharides from Escherichia coli were infused intravenously before initiation of a standardized global hypoxic-ischemic insult. The piglets were then randomized to either normothermia or therapeutic hypothermia. After 14 h, the piglets were evaluated. Our primary outcome was brain lactate/N-acetylaspartate ratio assessed by magnetic resonance spectroscopy. Secondary outcomes included measures of magnetic resonance imaging, amplitude-integrated electroencephalography, immunohistochemistry, and concentration of blood cells and cytokines.ResultsPiglets treated with and without therapeutic hypothermia were subjected to comparable global hypoxic-ischemic insults. We found no difference between the two groups with regards to measures of magnetic resonance spectroscopy and imaging, amplitude-integrated electroencephalography, immunohistochemistry, and concentration of blood cells and cytokines.ConclusionWe found no indication of neuroprotection by therapeutic hypothermia in newborn piglets following lipopolysaccharide-sensitized hypoxia-ischemia. However, interpretation of the results is limited by the short observation period. Further studies are required to determine the potential clinical implications of these findings.

Inhaled H2 or CO2 Do Not Augment the Neuroprotective Effect of Therapeutic Hypothermia in a Severe Neonatal Hypoxic-Ischemic Encephalopathy Piglet Model.

Hypoxic-ischemic encephalopathy (HIE) is still a major cause of neonatal death and disability as therapeutic hypothermia (TH) alone cannot afford sufficient neuroprotection. The present study investigated whether ventilation with molecular hydrogen (2.1% H2) or graded restoration of normocapnia with CO2 for 4 h after asphyxia would augment the neuroprotective effect of TH in a subacute (48 h) HIE piglet model. Piglets were randomized to untreated naïve, control-normothermia, asphyxia-normothermia (20-min 4%O2–20%CO2 ventilation; Tcore = 38.5 °C), asphyxia-hypothermia (A-HT, Tcore = 33.5 °C, 2–36 h post-asphyxia), A-HT + H2, or A-HT + CO2 treatment groups. Asphyxia elicited severe hypoxia (pO2 = 19 ± 5 mmHg) and mixed acidosis (pH = 6.79 ± 0.10). HIE development was confirmed by altered cerebral electrical activity and neuropathology. TH was significantly neuroprotective in the caudate nucleus but demonstrated virtually no such effect in the hippocampus. The mRNA levels of apoptosis-inducing factor and caspase-3 showed a ~10-fold increase in the A-HT group compared to naïve animals in the hippocampus but not in the caudate nucleus coinciding with the region-specific neuroprotective effect of TH. H2 or CO2 did not augment TH-induced neuroprotection in any brain areas; rather, CO2 even abolished the neuroprotective effect of TH in the caudate nucleus. In conclusion, the present findings do not support the use of these medical gases to supplement TH in HIE management.

No Added Neuroprotective Effect of Remote Ischemic Postconditioning and Therapeutic Hypothermia After Mild Hypoxia-Ischemia in a Piglet Model.

Introduction: Hypoxic ischemic encephalopathy (HIE) is a major cause of death and disability in children worldwide. Apart from supportive care, the only established treatment for HIE is therapeutic hypothermia (TH). As TH is only partly neuroprotective, there is a need for additional therapies. Intermittent periods of limb ischemia, called remote ischemic postconditioning (RIPC), have been shown to be neuroprotective after HIE in rats and piglets. However, it is unknown whether RIPC adds to the effect of TH. We tested the neuroprotective effect of RIPC with TH compared to TH alone using magnetic resonance imaging and spectroscopy (MRI/MRS) in a piglet HIE model.Methods: Thirty-two male and female piglets were subjected to 45-min global hypoxia-ischemia (HI). Twenty-six animals were randomized to TH or RIPC plus TH; six animals received supportive care only. TH was induced through whole-body cooling. RIPC was induced 1 h after HI by four cycles of 5 min of ischemia and 5 min of reperfusion in both hind limbs. Primary outcome was Lac/NAA ratio at 24 h measured by MRS. Secondary outcomes were NAA/Cr, diffusion-weighted imaging (DWI), arterial spin labeling, aEGG score, and blood oxygen dependent (BOLD) signal measured by MRI/MRS at 6, 12, and 24 h after the hypoxic-ischemic insult.Results: All groups were subjected to a comparable but mild insult. No difference was found between the two intervention groups in Lac/NAA ratio, NAA/Cr ratio, DWI, arterial spin labeling, or BOLD signal. NAA/Cr ratio at 24 h was higher in the two intervention groups compared to supportive care only. There was no difference in aEEG score between the three groups.Conclusion: Treatment with RIPC resulted in no additional neuroprotection when combined with TH. However, insult severity was mild and only evaluated at 24 h after HI with a short MRS echo time. In future studies more subtle neurological effects may be detected with increased MRS echo time and post mortem investigations, such as brain histology. Thus, the possible neuroprotective effect of RIPC needs further evaluation.

Hypothermia Attenuates Neuronal Damage via Inhibition of Microglial Activation, Including Suppression of Microglial Cytokine Production and Phagocytosis.

Although therapeutic hypothermia (TH) provides neuroprotection, the cellular mechanism underlying the neuroprotective effect of TH has not yet been fully elucidated. In the present study, we investigated the effect of TH on microglial activation to determine whether hypothermia attenuates neuronal damage via microglial activation. After lipopolysaccharide (LPS) stimulation, BV-2 microglia cells were cultured under normothermic (37°C) or hypothermic (33.5°C) conditions. Under hypothermic conditions, expression of pro-inflammatory cytokines and inducible nitric oxide synthase (iNOS) was suppressed. In addition, phagocytosis of latex beads was significantly suppressed in BV-2 cells under hypothermic conditions. Moreover, nuclear factor-κB signaling was inhibited under hypothermic conditions. Finally, neuronal damage was attenuated following LPS stimulation in neurons co-cultured with BV-2 cells under hypothermic conditions. In conclusion, hypothermia attenuates neuronal damage via inhibition of microglial activation, including microglial iNOS and pro-inflammatory cytokine expression and phagocytic activity. Investigating the mechanism of microglial activation regulation under hypothermic conditions could contribute to the development of novel neuroprotective therapies.

Prolonged astrocyte-derived erythropoietin expression attenuates neuronal damage under hypothermic conditions

BackgroundHypoxic-ischemic encephalopathy (HIE) has a high morbidity rate and involves severe neurologic deficits, including cerebral palsy. Therapeutic hypothermia (TH) has been shown to decrease the mortality rate and provide neuroprotection in infants with HIE. However, death and disability rates in HIE infants treated with TH remain high. Although the cellular mechanism of the neuroprotective effect of TH remains unclear, astrocytic erythropoietin (EPO) is known to be a key mediator of neuroprotection under hypoxic conditions. In the present study, we investigated the hypothermia effect on EPO expression in astrocytes and determined whether hypothermia attenuates neuronal damage via EPO signaling.MethodsAstrocytes derived from rat cerebral cortex were cultured under oxygen/glucose deprivation (OGD). The expression of EPO and hypoxia-inducible factor (HIF), a transcription factor of EPO, was assessed. After OGD, astrocytes were cultured under normothermic (37 °C) or hypothermic (33.5 °C) conditions, and then EPO and HIF expression was assessed. After OGD, rat cortical neurons were cultured in astrocyte-conditioned medium (ACM) derived from the hypothermic group, and neuronal apoptosis was evaluated.ResultsOGD induced EPO mRNA and protein expression, although at lower levels than hypoxia alone. HIF-1α and HIF-2α protein expression increased under hypoxia alone and OGD, although OGD increased HIF-2α protein expression less than hypoxia alone. EPO gene and protein expression after OGD was significantly higher under hypothermia. Moreover, expression of HIF-1α and HIF-2α protein was enhanced under hypothermia. In the presence of ACM derived from hypothermic astrocytes following OGD, the number of cleaved caspase 3 and TdT-mediated dUTP nick-end labeling-positive apoptotic neurons was lower than in the presence of ACM from normothermic astrocytes following OGD. Blockade of EPO signaling using anti-EPO neutralization antibody attenuated the anti-apoptotic effect of ACM derived from hypothermic astrocytes following OGD.ConclusionsHypothermia after OGD stabilized HIF-EPO signaling in astrocytes, and upregulated EPO expression could suppress neuronal apoptosis. Investigating the neuroprotective effect of EPO from astrocytes under hypothermic conditions may contribute to the development of novel neuroprotection-based therapies for HIE.

Outcome of Infants with Therapeutic Hypothermia after Perinatal Asphyxia and Early-Onset Sepsis

Background: Animal models suggest that neuroprotective effects of therapeutic hypothermia (TH) after perinatal asphyxia are reduced in infants with early-onset sepsis. Objectives: To assess the outcome of infants with perinatal asphyxia, neonatal encephalopathy, and TH in the presence of early-onset sepsis. Methods: In a retrospective cohort of 1,084 infants with perinatal asphyxia and TH, the outcome of 42 infants (gestational age 36.1–42.6 weeks and birth weight 2,280–5,240 g) with proven sepsis (n = 14) and probable sepsis (n = 28) was analyzed. Death, cerebral palsy, or a delayed development at 2 years was considered an adverse outcome. Results: Sepsis was caused mostly by group B streptococci (n = 17), other Gram-positive bacteria (n = 5), and Candida albicans (n = 1). Of the 42 infants, 9 (21.4%) died, and 5 (11.9%) showed impairments on follow-up. The outcome is comparable to the previously reported outcome of infants with TH without early-onset sepsis. Conclusion: A good outcome was reported in the majority of infants with perinatal asphyxia, TH, and early-onset sepsis. Cooling should not be withheld from these infants.

Serum calcium derangements in neonates with moderate to severe hypoxic ischemic encephalopathy and the impact of therapeutic hypothermia: a cohort study

Background: Perinatal hypoxia is a recognized cause of hypocalcemia in neonates in the first 3 days of life. Therapeutic hypothermia (TH) promotes neuroprotection by decreasing calcium influx into the cells during the reperfusion phase thereby increase serum calcium levels. This study examines the trends of serum calcium levels in neonates with hypoxic ischemic encephalopathy (HIE) and the effect of TH.Material and methods: A retrospective cohort study of neonates with moderate to severe HIE admitted to level III neonatal intensive care units (NICU’s) in Calgary between September 2011 and October 2015. HIE was staged using modified Sarnat scoring system. Ionized calcium levels were followed in the first 3 days of age.Results: One hundred thirteen neonates admitted with the diagnosis of moderate to severe HIE were included; 89 (79%) underwent TH. Hypercalcemia was significantly higher with TH 57 (64%) compared to 8 (33%) in noncooled group (p = .007). Hypocalcemia was less in TH group; 11 (12%) compared to 5 (21%) in non TH group. Hypo/hypercarbia did not alter the serum calcium levels. Furthermore; there was no increase in the incidence of intracranial hemorrhage, clinical or electrographic seizures, antiepileptic drug use, or hypoxic/ischemic MRI changes with calcium derangements.Conclusion: The incidence of hypocalcemia was reduced by almost half and hypercalcemia was significantly increased with TH in the first 3 days of life. The reduction in hypocalcemia and the increase in hypercalcemia may be attributed to the neuroprotective effect of TH.

Inhibition of dynamin-related protein 1 has neuroprotective effect comparable with therapeutic hypothermia in a rat model of cardiac arrest

Dynamin-related protein 1 (Drp1) regulates mitochondrial fission, it has been proven that inhibition of Drp1 by mdivi-1 improves survival and attenuates cerebral ischemic injury after cardiac arrest. In this study, we compared the effects of Drp1 inhibition with therapeutic hypothermia on post-resuscitation neurologic injury in a rat model of cardiac arrest. Rats were randomized into 4 groups: mdivi-1 treatment group (n = 39), hypothermic group (n = 38), normothermic group (n = 41), and sham group (n = 12). The rats in the mdivi-1 treatment group were received intravenously 1.2 mg/kg of mdivi-1 at 1 minute after the return of spontaneous circulation (ROSC). In rats in hypothermia group, rapid cooling was initiated at 5 minutes after resuscitation, and the core temperature was maintained to 33 ± 0.5°C for 2 hours. The results showed that both Drp1 inhibition and therapeutic hypothermia increased 3-day survival time (all P <0.05) and improved neurologic function up to 72 hours post cardiac arrest. In addition, both Drp1 inhibition and therapeutic hypothermia decreased cell injury, apoptosis in hippocampal cornu ammonis 1 region and brain mitochondrial dysfunction including adenosine triphosphate production, reactive oxygen species and mitochondrial membrane potential after cardiac arrest. Moreover, therapeutic hypothermia decreased mitochondrial Drp1 expression and mitochondrial fission after cardiac arrest. In conclusion, inhibition of Drp1 has a similar effect to therapeutic hypothermia on neurologic outcome after resuscitation in this cardiac arrest rat model, and the neuroprotective effects of therapeutic hypothermia are associated with inhibition of mitochondrial fission.

The effects of adding prophylactic phenobarbital to therapeutic hypothermia in the term-equivalent hypoxic-ischemic rat.

BackgroundHypoxic-ischemic encephalopathy (HIE) is a major cause of neonatal morbidity and mortality. Therapeutic hypothermia (TH) is the only available intervention, but neuroprotection is incomplete and variable. Seizures are common in infants with HIE undergoing TH and may worsen outcome. Phenobarbital (PB) is sometimes added, although use of prophylactic PB is controversial in the neonate. We hypothesize that prophylactic PB will not reduce, and may enhance, the neuroprotective effects of TH on brain injury and motor outcomes in the postnatal day 10 (P10) hypoxic-ischemic (HI) rat.MethodsP10 rat pups were subjected to unilateral HI and 4 h recovery with: normothermia (N); hypothermia (TH); and hypothermia with phenobarbital (TH+PB). Brain damage was assessed longitudinally at 24 h and 2 weeks using brain magnetic resonance imaging and 12 weeks using histochemical analysis. Motor function was assessed with the beam walk and cylinder tests.ResultsTH and TH+PB induced neuroprotection, as measured by global brain damage score and improved motor function. Exploratory analyses suggest that TH+PB may confer enhanced protection, especially to the extent of damage.ConclusionProphylactic PB with TH is not deleterious and may provide additional long-term neuroprotection, including improvement of motor outcomes following HI in the term-equivalent, neonatal rat.

Targeted Temperature Management and Acute Brain Injury: An Update from Recent Clinical Trials

The neuroprotective effects of therapeutic hypothermia—increasingly known as targeted temperature management (TTM)—have been recognized for decades, but translation into positive randomized clinical trial outcomes has proved difficult. Although there is level I evidence supporting TTM in adult cardiac arrest and neonatal hypoxic–ischemic encephalopathy, uncertainty remains about optimal temperature targets, exemplified by recent adult cardiac arrest data suggesting that cooling to 36 °C is equally as effective as cooling to 33 °C. For other forms of acute brain injury, the evidence supporting TTM is less clear and, in particular, recent traumatic brain injury trial data were disappointing. Further studies are required to address the logistics of implementing TTM in brain injury, including optimal temperature, timing of onset and duration, and complication management. In addition, further high-quality studies are needed to fully assess the role of TTM in stroke and other forms of acute brain injury.

Neuroprotective effect of therapeutic hypothermia versus standard care alone after convulsive status epilepticus: protocol of the multicentre randomised controlled trial HYBERNATUS.

Convulsive status epilepticus (CSE) is a major medical emergency associated with a 50 % morbidity rate. CSE guidelines have recommended prompt management for many years, but there is no evidence to date that they have significantly improved practices or outcomes. Developing neuroprotective strategies for use after CSE holds promise for diminishing morbidity and mortality rates. Hypothermia has been shown to afford neuroprotection in various health conditions. We therefore designed a trial to determine whether 90-day outcomes in mechanically ventilated patients with CSE requiring management in the intensive care unit (ICU) are improved by early therapeutic hypothermia (32–34 °C) for 24 h with propofol sedation. We are conducting a multicentre, open-label, parallel-group, randomised, controlled trial (HYBERNATUS) of potential neuroprotective effects of therapeutic hypothermia and routine propofol sedation started within 8 h after CSE onset in ICU patients requiring mechanical ventilation. Included patients are allocated to receive therapeutic hypothermia (32–34 °C) plus standard care or standard care alone. We plan to enrol 270 patients in 11 ICUs. An interim analysis is scheduled after the inclusion of 135 patients. The main study objective is to evaluate the effectiveness of therapeutic hypothermia (32–34 °C) for 24 h in diminishing 90-day morbidity and mortality (defined as a Glasgow Outcome Scale score <5). The HYBERNATUS trial is expected to a decreased proportion of patients with a Glasgow Outcome Scale score lower than 5 after CSE requiring ICU admission and mechanical ventilation.Trial registration Clinicaltrials.gov identifier NCT01359332 (registered on 23 May 2011)

Serum Calcium Derangements in Neonates with Hypoxic Ischemic Encephalopathy (HIE) With and Without Therapeutic Hypothermia

Abstract BACKGROUND: Perinatal hypoxia is a recognized cause of hypocalcemia in neonates in the first 3 days of age. However, therapeutic hypothermia (TH), the standard care for moderate to severe HIE, promotes neuropro-tection by decreasing calcium (Ca) influx into the cells during reperfusion phase. So TH can increase serum Ca levels and may even negate the hypo-calcemic effects in HIE. OBJECTIVES: To examine the trends in serum Ca levels in neonates with HIE with and without TH. DESIGN/METHODS: A retrospective cohort study of neonates with moderate to severe HIE admitted to a level III NICU between September 2011 and October 2015. HIE staging was done as per modified Sarnat’s scoring system. Hypercalcemia was defined as serum ionised Ca (iCa) &amp;gt;1.35 mmol/L and hypocalcemia was defined as serum iCa &amp;lt;0.9 mmol/L. Acidosis was considered if pH &amp;lt;7.2. Serum Ca and pH were followed in the first 3 days of age (Day 1-3). The relation of serum Ca levels with acidosis,seizures, intracranial hemorrhage, and MRI changes in neonates with and without TH was examined. Categorical variables were analysed using chi-square test. Logistic regression analysis was done to explore the association of hypo/hypercalcemia with various variables, adjusting for TH, HIE staging, and acidosis. RESULTS: Total number of neonates with moderate-severe HIE= 113; 89 neonates (79%) underwent TH. Incidence of hypercalcemia was 57/89 (88%) in the TH group whereas only one-third in the no TH group, whereas for hypocalcemia, it was 11/89(12%) and 5/24(21%) for the TH and no TH groups respectively. Hypercalcemia on Day 1 was significantly higher with TH(p 0.007) and acidosis(p 0.015). Hypocalcemia did not have any such association. Hypo/hypercarbia did not seem to alter the serum Ca levels. There was no increase in intracranial hemorrhage, clinical/EEG seizures, antiepileptic drug use or hypoxic MRI changes with Ca derangements. CONCLUSION: Incidence of hypocalcemia was reduced by almost half in TH group. Hypercalcemia on day 1 was significantly associated with TH and acidosis. On days 2 and 3, hypercalcemia occurred in TH even in the absence of acidosis, but the association was not statistically significant. Less hypocalcemia and more hypercalcemia in TH may be attributed to the neuroprotective effect of TH by inhibiting Ca influx into the cells. However, there was no correlation between Ca derangements and seizures or severity of hypoxic changes in MRI.

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

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

Hypothermia Reduces Toll-Like Receptor 3-Activated Microglial Interferon-βand Nitric Oxide Production

Therapeutic hypothermia protects neurons after injury to the central nervous system (CNS). Microglia express toll-like receptors (TLRs) that play significant roles in the pathogenesis of sterile CNS injury. To elucidate the possible mechanisms involved in the neuroprotective effect of therapeutic hypothermia, we examined the effects of hypothermic culture on TLR3-activated microglial release of interferon (IFN)-β and nitric oxide (NO), which are known to be associated with neuronal cell death. When rat or mouse microglia were cultured under conditions of hypothermia (33°C) and normothermia (37°C) with a TLR3 agonist, polyinosinic-polycytidylic acid, the production of IFN-β and NO in TLR3-activated microglia at 48 h was decreased by hypothermia compared with that by normothermia. In addition, exposure to recombinant IFN-β and sodium nitroprusside, an NO donor, caused death of rat neuronal pheochromocytoma PC12 cells in a concentration-dependent manner after 24 h. Taken together, these results suggest that the attenuation of microglial production of IFN-β and NO by therapeutic hypothermia leads to the inhibition of neuronal cell death.

Controlled prophylactic normothermia

Fever is a very frequent complication of intensive care treatment and an independent predictor of unfavourable outcome and mortality in most patients with an acute severe neurologic injury. Today not only treatment but even more prevention of fever has become the focus of intensivists. Preliminary animal data for the beneficial neuroprotective effect of therapeutic hypothermia could not satisfyingly be reproduced in patients raising questions about the possible side effects of hypothermia. Controlled prophylactic normothermia (36.5°C) prevents secondary injury through consequent treatment of fever and limits dose-dependent side effects through therapeutic hypothermia. Novel endovascular and gel-pad surface cooling measures have shown to be feasible and efficacious in inducing and maintaining even long-term controlled normothermia.

The “Refrige-a-RAT-or”: An Accurate, Inexpensive, and Clinically Relevant Small Animal Model of Therapeutic Hypothermia

Physical and molecular mechanisms for the neuroprotective effect of therapeutic hypothermia are not completely understood, and new therapeutic applications incorporating hypothermia remain to be developed and tested. Clinically relevant animal models of therapeutic hypothermia are not well established or consistent. The objective was to develop and test an inexpensive small animal therapeutic hypothermia system that models those in widespread clinical use and verify that such a system confers neuroprotection in a rat model of global brain ischemia. A water-cooled extracorporeal system and attendant anesthesia/sedation protocol were developed and tested. In Stage 1, animals were instrumented for brain, temporalis, and rectal temperature monitoring, and the system was tested for its effect on temperature and hemodynamics. In Stage 2, animals were instrumented for rectal temperature only, subjected to global brain ischemia by two-vessel occlusion and hypotension for 8 minutes, and given either sham therapy (37°C) or hypothermia (32°C) for 4 hours. Viable CA1 neurons were counted at 7 days. The system was well tolerated, provided exquisite control of animal core and brain temperatures, and conferred robust neuroprotection at 7 days. The median and interquartile ranges (IQRs) of viable neurons per 300-μm field were 130 (IQR = 128 to 135) for sham control, 19 (IQR = 15 to 30) for untreated ischemic animals, and 101 (IQR = 94 to 113) for ischemic animals treated with hypothermia (p < 0.05 for comparison between all groups). Like human protocols, this model incorporates sedation and analgesia, results in robust neuroprotection, is well tolerated, and offers exquisite temperature control. The system is noninvasive and inexpensive and offers a model that is similar to methods used in clinical practice. This system will be of interest to investigators using small animal models to examine neuroprotective mechanisms of hypothermia and translational strategies that combine hypothermia with targeted pharmacotherapy.

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

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. 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. 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. 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.

Reanimation des Neugeborenen

Although almost 10% of all newborn infants need some form of respiratory assistance after birth, only 1% will require more advanced forms of resuscitation. Because these rare events cannot always be anticipated, pediatricians and neonatologists may not be readily available and resuscitation will have to be performed by anesthesiologists. In recent years, international guidelines for neonatal resuscitation have been revised by the International Liaison Committee on Resuscitation (ILCOR), the American Academy of Pediatrics (AAP) and the American Heart Association (AHA), as well as the European Resuscitation Council (ERC). The revised guidelines describe a simplified resuscitation algorithm which emphasizes the central role of respiratory support and an increase in heart rate is judged to be the best marker for successful ventilation. In deliveries complicated by meconium-stained amniotic fluid, intrapartum suctioning of the oropharynx is no longer recommended and endotracheal suctioning is restricted to severely depressed babies. The new guidelines mention the use of the laryngeal mask airway (LMA) and CO(2) detectors without, however, making firm recommendations. The use of 100% oxygen in neonatal resuscitation is increasingly being challenged. In the rare event of a newborn whose heart rate drops below 60 beats/min, more advanced resuscitation (chest compressions using the 2-thumb-encircling-hands technique, epinephrine 10-30 mug/kgBW i.v.) will be required. Finally, the guidelines mention the possible neuroprotective effect of therapeutic hypothermia after asphyxia, but finally only recommend that hyperthermia should be avoided.