Effect of moderate hypothermia on lipid peroxidation in canine brain tissue after cardiac arrest and resuscitation

The Effect of Targeted Temperature Therapy on Antioxidant Levels in Patients With Spontaneous Circulation After Cardiac Arrest

Introduction In this study, we aimed to measure the change in total antioxidant status (TAS), total oxidant stress (TOS), oxidative stress index (OSI), and nuclear factor erythroid 2 (Nrf-2) levels during the treatment period in patients who restored spontaneous circulation return after cardiac arrest with targeted temperature management (TTM) therapy in our hospital. Methods The study included 36 patients who were hospitalized in the anesthesia intensive care unit and coronary intensive care unit of our hospital and were treated with TTM therapy after cardiac arrest. TAS, TOS, OSI, and Nrf-2 levels were measured at 0 (beginning), 12, 24, and 48 (end) hours of TTM therapy. Results The mean age of the patients participating in the study was 54.25±17.10. TAS and TOS levels decreased gradually during TTM therapy, but statistically significant decrease was observed at the end of the hour. When Nrf-2 and OSI levels were evaluated, it was found that no statistically significant difference was observed during the TTM therapy. Conclusion In our study, the oxidant-antioxidant balance was preserved in patients who received TTM therapy after cardiac arrest. We predict TTM therapy is effective on oxidative stress after cardiac arrest and should be applied for at least 48 hours.

Pharmacological Approach for Neuroprotection After Cardiac Arrest-A Narrative Review of Current Therapies and Future Neuroprotective Cocktail

Cardiac arrest (CA) results in global ischemia-reperfusion injury damaging tissues in the whole body. The landscape of therapeutic interventions in resuscitation medicine has evolved from focusing solely on achieving return of circulation to now exploring options to mitigate brain injury and preserve brain function after CA. CA pathology includes mitochondrial damage and endoplasmic reticulum stress response, increased generation of reactive oxygen species, neuroinflammation, and neuronal excitotoxic death. Current non-pharmacologic therapies, such as therapeutic hypothermia and extracorporeal cardiopulmonary resuscitation, have shown benefits in protecting against ischemic brain injury and improving neurological outcomes post-CA, yet their application is difficult to institute ubiquitously. The current preclinical pharmacopeia to address CA and the resulting brain injury utilizes drugs that often target singular pathways and have been difficult to translate from the bench to the clinic. Furthermore, the limited combination therapies that have been attempted have shown mixed effects in conferring neuroprotection and improving survival post-CA. The global scale of CA damage and its resultant brain injury necessitates the future of CA interventions to simultaneously target multiple pathways and alleviate the hemodynamic, mitochondrial, metabolic, oxidative, and inflammatory processes in the brain. This narrative review seeks to highlight the current field of post-CA neuroprotective pharmaceutical therapies, both singular and combination, and discuss the use of an extensive multi-drug cocktail therapy as a novel approach to treat CA-mediated dysregulation of multiple pathways, enhancing survival, and neuroprotection.

Practical considerations for postarrest targeted temperature management

Out-of-hospital cardiac arrest remains a major challenge worldwide, with survival to discharge rates of <20% in the great majority of countries. Advancements in prehospital care, including increasing deployment of automated external defibrillators and improvements in bystander cardiopulmonary resuscitation, have led to more victims achieving return of spontaneous circulation (ROSC), yet the majority of patients with ROSC suffer in-hospital mortality or significant neurologic injuries that persist after discharge. This postarrest morbidity and mortality is largely due to a complex syndrome of mitochondrial dysfunction, inflammatory cascades and cellular injuries known as the postcardiac arrest syndrome (PCAS). The management of PCAS represents a formidable task for emergency and critical care providers. A cornerstone of PCAS treatment is the use of aggressive core body temperature control using thermostatically controlled devices, known as targeted temperature management (TTM). This therapy, demonstrated to be effective in improving both survival and neurologic recovery by several randomized controlled trials nearly 20 years ago, remains a major topic of clinical investigation. Important practical questions about TTM remain: How soon must providers initiate the therapy? What TTM goal temperature maximizes benefit while limiting potential adverse effects? How long should TTM therapy be continued in patients following resuscitation? In this review, we will address these issues and summarize clinical research over the past decade that has added to our fund of knowledge surrounding this important treatment of patients following cardiac arrest.

Hydrogen gas inhalation alleviates oxidative stress in patients with post-cardiac arrest syndrome

Oxidative stress plays a key role in the pathophysiology of post-cardiac arrest syndrome. Molecular hydrogen reduces oxidative stress and exerts anti-inflammatory effects in an animal model of cardiac arrest. However, its effect on human post-cardiac arrest syndrome is unclear. We consecutively enrolled five comatose post-cardiac arrest patients (three males; mean age, 65 ± 15 years; four cardiogenic, one septic cardiac arrest) and evaluated temporal changes in oxidative stress markers and cytokines with inhaled hydrogen. All patients were treated with target temperature management. Hydrogen gas inhalation (2% hydrogen with titrated oxygen) was initiated upon admission for 18 h. Blood hydrogen concentrations, plasma and urine oxidative stress markers (derivatives of reactive oxygen metabolites, biological antioxidant potential, 8-hydroxy-2'-deoxyguanosine, N^ɛ-hexanoyl-lysine, lipid hydroperoxide), and cytokines (interleukin-6 and tumor necrosis factor-α) were measured before and 3, 9, 18, and 24 h after hydrogen gas inhalation. Arterial hydrogen concentration was measurable and it was equilibrated with inhaled hydrogen. Oxidative stress was reduced and cytokine levels were unchanged in cardiogenic patients, whereas oxidative stress was unchanged and cytokine levels were diminished in the septic patient. The effect of inhaled hydrogen on oxidative stress and cytokines in comatose post-cardiac arrest patients remains indefinite because of methodological weaknesses.

Therapeutic hypothermia to reduce intracranial pressure after traumatic brain injury: the Eurotherm3235 RCT

BACKGROUND

Traumatic brain injury (TBI) is a major cause of disability and death in young adults worldwide. It results in around 1 million hospital admissions annually in the European Union (EU), causes a majority of the 50,000 deaths from road traffic accidents and leaves a further ≈10,000 people severely disabled.

OBJECTIVE

The Eurotherm3235 Trial was a pragmatic trial examining the effectiveness of hypothermia (32-35 °C) to reduce raised intracranial pressure (ICP) following severe TBI and reduce morbidity and mortality 6 months after TBI.

DESIGN

An international, multicentre, randomised controlled trial.

SETTING

Specialist neurological critical care units.

PARTICIPANTS

We included adult participants following TBI. Eligible patients had ICP monitoring in place with an ICP of > 20 mmHg despite first-line treatments. Participants were randomised to receive standard care with the addition of hypothermia (32-35 °C) or standard care alone. Online randomisation and the use of an electronic case report form (CRF) ensured concealment of random treatment allocation. It was not possible to blind local investigators to allocation as it was obvious which participants were receiving hypothermia. We collected information on how well the participant had recovered 6 months after injury. This information was provided either by the participant themself (if they were able) and/or a person close to them by completing the Glasgow Outcome Scale - Extended (GOSE) questionnaire. Telephone follow-up was carried out by a blinded independent clinician.

INTERVENTIONS

The primary intervention to reduce ICP in the hypothermia group after randomisation was induction of hypothermia. Core temperature was initially reduced to 35 °C and decreased incrementally to a lower limit of 32 °C if necessary to maintain ICP at < 20 mmHg. Rewarming began after 48 hours if ICP remained controlled. Participants in the standard-care group received usual care at that centre, but without hypothermia.

MAIN OUTCOME MEASURES

The primary outcome measure was the GOSE [range 1 (dead) to 8 (upper good recovery)] at 6 months after the injury as assessed by an independent collaborator, blind to the intervention. A priori subgroup analysis tested the relationship between minimisation factors including being aged < 45 years, having a post-resuscitation Glasgow Coma Scale (GCS) motor score of < 2 on admission, having a time from injury of < 12 hours and patient outcome.

RESULTS

We enrolled 387 patients from 47 centres in 18 countries. The trial was closed to recruitment following concerns raised by the Data and Safety Monitoring Committee in October 2014. On an intention-to-treat basis, 195 participants were randomised to hypothermia treatment and 192 to standard care. Regarding participant outcome, there was a higher mortality rate and poorer functional recovery at 6 months in the hypothermia group. The adjusted common odds ratio (OR) for the primary statistical analysis of the GOSE was 1.54 [95% confidence interval (CI) 1.03 to 2.31]; when the GOSE was dichotomised the OR was 1.74 (95% CI 1.09 to 2.77). Both results favoured standard care alone. In this pragmatic study, we did not collect data on adverse events. Data on serious adverse events (SAEs) were collected but were subject to reporting bias, with most SAEs being reported in the hypothermia group.

CONCLUSIONS

In participants following TBI and with an ICP of > 20 mmHg, titrated therapeutic hypothermia successfully reduced ICP but led to a higher mortality rate and worse functional outcome.

LIMITATIONS

Inability to blind treatment allocation as it was obvious which participants were randomised to the hypothermia group; there was biased recording of SAEs in the hypothermia group. We now believe that more adequately powered clinical trials of common therapies used to reduce ICP, such as hypertonic therapy, barbiturates and hyperventilation, are required to assess their potential benefits and risks to patients.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN34555414.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 22, No. 45. See the NIHR Journals Library website for further project information. The European Society of Intensive Care Medicine supported the pilot phase of this trial.

A New Vision for Therapeutic Hypothermia in the Era of Targeted Temperature Management: A Speculative Synthesis

Three decades of animal studies have reproducibly shown that hypothermia is profoundly cerebroprotective during or after a central nervous system (CNS) insult. The success of hypothermia in preclinical acute brain injury has not only fostered continued interest in research on the classic secondary injury mechanisms that are prevented or blunted by hypothermia but has also sparked a surge of new interest in elucidating beneficial signaling molecules that are increased by cooling. Ironically, while research into cold-induced neuroprotection is enjoying newfound interest in chronic neurodegenerative disease, conversely, the scope of the utility of therapeutic hypothermia (TH) across the field of acute brain injury is somewhat controversial and remains to be fully defined. This has led to the era of Targeted Temperature Management, which emphasizes a wider range of temperatures (33–36°C) showing benefit in acute brain injury. In this comprehensive review, we focus on our current understandings of the novel neuroprotective mechanisms activated by TH, and discuss the critical importance of developmental age germane to its clinical efficacy. We review emerging data on four cold stress hormones and three cold shock proteins that have generated new interest in hypothermia in the field of CNS injury, to create a framework for new frontiers in TH research. We make the case that further elucidation of novel cold responsive pathways might lead to major breakthroughs in the treatment of acute brain injury, chronic neurological diseases, and have broad potential implications for medicines of the distant future, including scenarios such as the prevention of adverse effects of long-duration spaceflight, among others. Finally, we introduce several new phrases that readily summarize the essence of the major concepts outlined by this review—namely, Ultramild Hypothermia, the “Responsivity of Cold Stress Pathways,” and “Hypothermia in a Syringe.”

Therapeutic hypothermia in acute traumatic spinal cord injury

Therapeutic hypothermia is already widely acknowledged as an effective neuroprotective intervention, especially within the acute care setting in relation to conditions such as cardiac arrest and neonatal encephalopathy. Its multifactorial mechanisms of action, including lowering metabolic rate and reducing acute inflammatory cellular processes, ultimately provide protection for central nervous tissue from continuing injury following ischaemic or traumatic insult. Its clinical application within acute traumatic spinal cord injury would therefore seem very plausible, it having the potential to combat the pathophysiological secondary injury processes that can develop in the proceeding hours to days following the initial injury. As such it could offer invaluable assistance to lessen subsequent sensory, motor and autonomic dysfunction for an individual affected by this devastating condition. Yet research surrounding this intervention's applicability in this field is somewhat lacking, the majority being experimental. Despite a recent resurgence of interest, which in turn has produced encouraging results, there is a real possibility that this potentially transformational intervention for treating traumatic spinal cord injury could remain an experimental therapy and never reach clinical implementation.

Assessment of oxidative stress after out-of-hospital cardiac arrest

INTRODUCTION

Pathophysiology of cardiac arrest corresponds to a whole body ischemia-reperfusion. This phenomenon is usually associated with an oxidative stress in various settings, but few data are available on cardiac arrest in human. The aim of the present study was to evaluate different oxidative stress markers in out-of-hospital cardiac arrest (OHCA) patients treated with therapeutic hypothermia.

MATERIALS AND METHODS

We conducted a prospective study assessing oxidative stress markers (thiobarbituric acid reactive species, carbonyls, thiols, glutathione, and glutathione peroxidase) in OHCA patients treated with therapeutic hypothermia. Measurements were performed during the 4 days after admission and compared between good and poor outcome patients according to Cerebral Performance Category.

RESULTS

Thirty-four patients were included, 10 good and 24 poor outcomes at 6 months. Thiobarbituric acid reactive species were higher in the poor outcome group on admission and when therapeutic hypothermia was reached. The other markers were not different between groups. No markers seemed modified by the use of therapeutic hypothermia in each group.

CONCLUSIONS

After OHCA, good outcome patients exhibit lower oxidative stress markers than poor outcome patients. Thiobarbituric acid reactive species appears to be an early prognostic parameter. Oxidative stress markers seem not mitigated by therapeutic hypothermia.

Therapeutic hypothermia applicable to cardiac surgery

OBJECTIVE

To review the beneficial and adverse effects of therapeutic hypothermia (TH) applicable to cardiac surgery with cardiopulmonary bypass (CPB) in the contexts of various temperature levels and techniques for achieving TH.

DATABASES USED

Multiple electronic literature searches were performed using PubMed and Google for articles published from June 2012 to December 2014. Relevant terms (e.g. 'hypothermia', 'cardiopulmonary bypass', 'cardiac surgery', 'neuroprotection') were used to search for original articles, letters and reviews without species limitation. Reviews were included despite potential publication bias. References from the studies identified were also searched to find other potentially relevant citations. Abstracts, case reports, conference presentations, editorials and expert opinions were excluded.

CONCLUSIONS

Therapeutic hypothermia is an essential measure of neuroprotection during cardiac surgery that may be achieved most effectively by intravascular cooling using hypothermic CPB. For most cardiac surgical procedures, mild to modest (32-36 °C) TH will be sufficient to assure neuroprotection and will avoid most of the adverse effects of hypothermia that occur at lower body core temperatures.

Evaluation and comparison of the effect of hypothermia and ozone on ischemia-reperfusion injury of skeletal muscle in rats

BACKGROUND

Tourniquet-induced ischemia-reperfusion, which affects local and distant organs, is very common in orthopedic surgery. Hypothermia is used in traumatic tissue during ischemic period commonly. Ozone (O3) has been recommended as a novel therapeutic agent in various medical conditions. The objective of the study was to evaluate and compare the effect of hypothermia (H) and O3 on ischemia-reperfusion injury of skeletal muscle in rats by measuring oxidative parameters and inducible nitric oxide synthase (iNOS) levels.

MATERIALS AND METHODS

Eighteen rats (Wistar albino) were separated into five groups randomly (sham, IR, IR + H, IR + O3, IR + H + O3; n = 6). The lower right extremity of all rats was subjected to 2 h of ischemia and 22 h of reperfusion clamping the common iliac artery and using the rubber-band technique at the level of the lesser trochanter under general anesthesia. Two hours of hypothermia were applied during the first 2 h of reperfusion in two groups. O3 was applied in two groups. All rats were sacrificed after the IR period with high dose of anesthesia. The tibialis anterior muscle and blood were saved. Levels of superoxide dismutase, glutathione peroxidase, MDA, NOx, and interleukin-1β were measured in the muscle. Creatinine kinase, lactate dehydrogenase, aspartate aminotransferase, urea, creatinine, and electrolytes were measured in serum. Immunohistochemical iNOS staining was performed on muscle samples.

RESULTS

The levels of MDA, NOx, and interleukin-1β in muscle were raised in the IR group compared with those in the sham group. The same parameters were lower in the groups of IR + H, IR + O3, and IR + H + O3 compared with those in the IR group. Superoxide dismutase and glutathione peroxidase activities in muscle were lower in the IR group compared with those in the sham group; however, same parameters were higher in the groups of IR + H, IR + O3, and IR + H + O3 compared with those in the IR group. Score and intensity of iNOS staining in skeletal muscle in the IR group was increased compared with that in the sham group and decreased in the groups of IR + H, IR + O3, and IR + H + O3 compared with that in the IR group. Levels of creatinine kinase, aspartate aminotransferase, and K in the three treatment groups decreased compared with those in the IR group.

CONCLUSIONS

These findings showed that hypothermia, which has more affect, and O3 decreased the tourniquet-induced IR injury in the rat's muscle-skeletal system by reducing the levels of oxidative and nitrosative stress parameters and enhancing antioxidant enzymes. Hypothermia and O3 had no synergistic effect. Hypothermic reperfusion and O3 preconditioning might be beneficial in skeletal muscle IR injury-associated tourniquet.

Effects of hypothermia on skeletal ischemia reperfusion injury in rats

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Stem cell therapy for neonatal hypoxic-ischemic encephalopathy

Treatments for neonatal hypoxic-ischemic encephalopathy (HIE) have been limited. The aim of this paper is to offer translational research guidance on stem cell therapy for neonatal HIE by examining clinically relevant animal models, practical stem cell sources, safety and efficacy of endpoint assays, as well as a general understanding of modes of action of this cellular therapy. In order to do so, we discuss the clinical manifestations of HIE, highlighting its overlapping pathologies with stroke and providing insights on the potential of cell therapy currently investigated in stroke, for HIE. To this end, we draw guidance from recommendations outlined in stem cell therapeutics as an emerging paradigm for stroke or STEPS, which have been recently modified to Baby STEPS to cater for the “neonatal” symptoms of HIE. These guidelines recognized that neonatal HIE exhibit distinct disease symptoms from adult stroke in need of an innovative translational approach that facilitates the entry of cell therapy in the clinic. Finally, new information about recent clinical trials and insights into combination therapy are provided with the vision that stem cell therapy may benefit from available treatments, such as hypothermia, already being tested in children diagnosed with HIE.

Advancing critical care medicine with stem cell therapy and hypothermia for cerebral palsy

With limited clinical trials on stem cell therapy for adult stroke underway, the assessment of efficacy also needs to be considered for neonatal hypoxic-ischemic brain injury, considering its distinct symptoms. The critical nature of this condition leads to establishment of deficits that last a lifetime. Here, we will highlight the progress of current translational research, commenting on the critical nature of the disease, stem cell sources, the use of hypothermia, safety and efficacy of each treatment, modes of action, and the possibility of combination therapy. With this in mind, we reference translational guidelines established by a consortium of research partners called Stem cell Therapeutics as an Emerging Paradigm for Stroke (STEPS). The guidelines of STEPS are directed toward evaluating outcomes of cell therapy in adult stroke; however, we identify the overlapping pathology, as we believe that these guidelines will serve well in the investigation of neonatal hypoxic-ischemic therapy. Finally, we discuss emerging treatments and a case report, altogether suggesting that the potential for these treatments to be used in synergy has arrived and the time for advancing stem cell use in combination with hypothermia for cerebral palsy is now.

The use of modest systemic hypothermia after iatrogenic spinal cord injury during surgery

Iatrogenic spinal cord injury (SCI) is an uncommon (0%-3%), yet devastating, complication of spine surgery. Recent evidence based on small clinical studies indicates that modest hypothermia is a feasible treatment option for severe SCI. We extended this treatment modality to patients with devastating iatrogenic SCI. We conducted a retrospective case series of five male patients (cervical trauma--1, cervical degenerative--2, thoracic trauma--1, and thoracic scoliosis--1) with an age range of 16-51 years (average age of 46 years) with intraoperative motor-evoked potential/somatosensory-evoked potential loss secondary to catastrophic events during the spinal operation associated with new SCI. Modest hypothermia was instituted immediately postsurgery for 24 hours. Four patients also received methylprednisolone. Preoperative American Spinal Injury Association (ASIA) scores were D (n=3) and E (n=2), while immediate postoperative scores were A (n=1), B (n=1), C (n=2), and D (n=1). Immediate postoperative MRI revealed new cord signal change in three patients. Two patients required subsequent surgery. ASIA scores at last follow-up were C (n=1), D (n=3), and E (n=1) with an improvement of 1-2 grades per patient. Adverse events such as pulmonary embolism, deep venous thrombosis, coagulopathy, or infection were not observed. Hypothermia is a feasible treatment option for patients with iatrogenic SCI. While hypothermia has not been proven to improve outcomes in these situations, aggressive medical management, including cooling, resulted in better-than-expected outcomes in this small cohort.

Therapeutic hypothermia following cardiac arrest

More than 10 years ago, the randomised studies of therapeutic hypothermia after cardiac arrest showed significant improvement of neurological outcome and survival. Since then, it has become clear that most of the possible adverse events of therapeutic hypothermia are mild and can easily be controlled by proper administration of intensive care. Although implementation of this effective therapy is quite successful, many questions of the exact treatment protocol still remain unanswered. Therapeutic hypothermia treatment therefore must be tailored to the specific patient's needs. Hence, the exact level of target temperature, duration of cooling, rewarming, timing of the therapy and concomitant medication to facilitate therapeutic hypothermia will be important in the future. Additionally, the use of a post-resuscitation treatment bundle (specialised cardiac-arrest centres including intensive post-resuscitation care, appropriate haemodynamic and respiratory management, therapeutic hypothermia and percutaneous coronary intervention) could further improve treatment of cardiac arrest.

Mechanisms of hypothermic neuroprotection

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

The mechanisms and treatment of asphyxial encephalopathy

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

The influence of deep hypothermia on inflammatory status, tissue hypoxia and endocrine function of adipose tissue during cardiac surgery

Changes in endocrine function of adipose tissue during surgery, such as excessive production of proinflammatory cytokines, can significantly alter metabolic response to surgery and worsen its outcomes and prognosis of patients. Therapeutic hypothermia has been used to prevent damage connected with perioperative ischemia and hypoperfusion. The aim of our study was to explore the influence of deep hypothermia on systemic and local inflammation, adipose tissue hypoxia and adipocytokine production. We compared serum concentrations of proinflammatory markers (CRP, IL-6, IL-8, sIL-2R, sTNFRI, PCT) and mRNA expression of selected genes involved in inflammatory reactions (IL-6, TNF-α, MCP-1, MIF) and adaptation to hypoxia and oxidative stress (HIF1-α, MT3, GLUT1, IRS1, GPX1, BCL-2) in subcutaneous and visceral adipose tissue and in isolated adipocytes of patients undergoing cardiosurgical operation with hypothermic period. Deep hypothermia significantly delayed the onset of surgery-related systemic inflammatory response. The relative gene expression of the studied genes was not altered during the hypothermic period, but was significantly changed in six out of ten studied genes (IL-6, MCP-1, TNF-α, HIF1-α, GLUT1, GPX1) at the end of surgery. Our results show that deep hypothermia suppresses the development of systemic inflammatory response, delays the onset of local adipose tissue inflammation and thus may protect against excessive expression of proinflammatory and hypoxia-related factors in patients undergoing elective cardiac surgery procedure.

Role of transient receptor potential channel 1 (TRPC1) in glutamate-induced cell death in the hippocampal cell line HT22

Transient receptor potential channel 1 (TRPC1; a cation channel activated by store depletion and/or through an intracellular messenger) is expressed in a variety of tissues, including the brain. To study the physiological function of TRPC1, we investigated the role of endogenously expressed TRPC1 in glutamate-induced cell death, using the murine hippocampal cell line HT22. Knocking down TRPC1 mRNA using TRPC1-shRNA or blocking of TRPC channels using 2-APB (≥200 μM) robustly attenuated glutamate-induced cell death after 24 h of incubation with 5 mM glutamate. Glutamate toxicity in HT22 cells seems to involve metabotropic glutamate receptor mGluR5 since MPEP (2-methyl-6-(phenylethynyl)-pyridine), an mGluR5 antagonist (≥100 μM), abrogated glutamate toxicity. Furthermore, a direct activation of mGluR5 by CHPG [(RS)-chloro-5-hydroxyphenylglycine; 100 μM or 300 μM] promoted HT22 cell death. TRPC1 knock-down markedly reduced CHPG-induced cell death. These observations suggest that glutamate-induced cell death in HT22 cells activates mGluR5 receptors, which significantly increases Ca(2+) influx through TRPC1 channels. TRPC1 knock-down prevented glutamate- and CHPG-induced cell death, suggesting that glutamate-induced toxicity in HT22 cells is mediated through TRPC1 channels and an mGluR5-dependent pathway. Together, this work provides evidence for a novel receptor activation pathway of TRPC1 in glutamate-induced toxicity.

Status of systemic oxidative stress during therapeutic hypothermia in patients with post-cardiac arrest syndrome

Therapeutic hypothermia (TH) is thought to be due to the downregulation of free radical production, although the details of this process remain unclear. Here, we investigate changes in oxidative stress and endogenous biological antioxidant potential during TH in patients with post-cardiac arrest syndrome (PCAS). Nineteen PCAS patients were enrolled in the study. Brain temperature was decreased to the target temperature of 33°C, and it was maintained for 24 h. Patients were rewarmed slowly (0.1°C/h, <1°C/day). The generation of reactive oxygen metabolites (ROMs) was evaluated in plasma samples by d-ROM test. Plasma antioxidant capacity was measured by the biological antioxidant potential (BAP) test. Levels of d-ROMs and BAP levels during the hypothermic stage (33°C) were suppressed significantly compared with pre-TH induction levels (P < 0.05), while both d-ROM and BAP levels increased with rewarming (33-36°C) and were correlated with brain temperature. Clinical monitoring of oxidative stress and antioxidant potential is useful for evaluating the redox state of patients undergoing TH after PCAS. Additional therapy to support the antioxidant potential in the rewarming stage following TH may reduce some of the observed side effects associated with the use of TH.

Hypothermia as a neuroprotective strategy in subarachnoid hemorrhage: a pathophysiological review focusing on the acute phase

Aneurysmal subarachnoid hemorrhage (SAH) remains a very prevalent challenge in neurosurgery associated with a high morbidity and mortality due to the lack of specific treatment modalities. The prognosis of SAH patients depends primarily on three factors: (i) the severity of the initial bleed, (ii) the endovascular or neurosurgical procedure to occlude the aneurysm and (iii) the occurrence of late sequelae, namely delayed ischemic neurological deficits due to cerebral vasospasm. While neurosurgeons and interventionalists have put significant efforts in minimizing periprocedural complications and a multitude of investigators have been devoted to the research on chronic vasospasm, the acute phase of SAH has not been studied in comparable detail. In various experimental studies during the past decade, hypothermia has been shown to reduce neuronal damage after ischemia, traumatic brain injury and other cerebrovascular diseases. Clinically, only some of these encouraging results could be reproduced. This review analyses results of studies on the effects of hypothermia on SAH with special respect to the acute phase in an experimental setting. Based on the available data, some considerations for the application of mild to moderate hypothermia in patients with subarachnoid hemorrhage are given.

ADVANCES IN THE CELL-BASED TREATMENT OF NEONATAL HYPOXIC-ISCHEMIC BRAIN INJURY

Stem cell therapy for adult stroke has reached limited clinical trials. Here, we provide translational research guidance on stem cell therapy for neonatal hypoxic-ischemic brain injury requiring a careful consideration of clinically relevant animal models, feasible stem cell sources, and validated safety and efficacy endpoint assays, as well as a general understanding of modes of action of this cellular therapy. To this end, we refer to existing translational guidelines, in particular the recommendations outlined in the consortium of academicians, industry partners and regulators called Stem cell Therapeutics as an Emerging Paradigm for Stroke or STEPS. Although the STEPS guidelines are directed at enhancing the successful outcome of cell therapy in adult stroke, we highlight overlapping pathologies between adult stroke and neonatal hypoxic-ischemic brain injury. We are, however, cognizant that the neonatal hypoxic-ischemic brain injury displays disease symptoms distinct from adult stroke in need of an innovative translational approach that facilitates the entry of cell therapy in the clinic. Finally, insights into combination therapy are provided with the vision that stem cell therapy may benefit from available treatments, such as hypothermia, already being tested in children diagnosed with hypoxic-ischemic brain injury.

Nitrotyrosine and nitrate/nitrite levels in cardiac arrest survivors treated with endovascular hypothermia

The protective effect of therapeutic hypothermia in cardiac arrest survivors (CAS) has been previously well documented. Animal studies have indicated that attenuation of tissue oxidative stress (OS) may be involved in the mechanisms that lead to the beneficial effect of hypothermia. The extent of OS and nitric oxide (NO) production in adult CAS treated with endovascular hypothermia is, however, unknown. A total of 11 adult patients who experienced cardiac arrest out of hospital were included in the present study, and all were treated with mild hypothermia using the Thermogard XP (Alsius, USA) endovascular system. A target core temperature of 33 °C was maintained for 24 hours, with a subsequent rewarming rate of 0.15 °C per hour, followed by normothermia at 36.8 °C. Blood samples for the measurement of nitrotyrosine and nitrate/nitrite levels were drawn at admission and every 6 hours thereafter for two days. During the hypothermic period, the levels of nitrotyrosine and nitrates/nitrites were comparable with baseline values. During the rewarming period, serum levels of both parameters gradually increased and, during the normothermic period, the levels were significantly higher compared with hypothermic levels (nitrotyrosine, P<0.001; nitrates/nitrites, P<0.05). In our study, significantly lower levels of nitrotyrosine and nitrates/nitrites were demonstrated during hypothermia compared with levels during the normothermic period in adult CAS. These data suggest that attenuation of OS and NO production may be involved in the protective effect of hypothermia in adult CAS.

Mild hypothermia attenuates mitochondrial oxidative stress by protecting respiratory enzymes and upregulating MnSOD in a pig model of cardiac arrest

Mild hypothermia is the only effective treatment confirmed clinically to improve neurological outcomes for comatose patients with cardiac arrest. However, the underlying mechanism is not fully elucidated. In this study, our aim was to determine the effect of mild hypothermia on mitochondrial oxidative stress in the cerebral cortex. We intravascularly induced mild hypothermia (33°C), maintained this temperature for 12 h, and actively rewarmed in the inbred Chinese Wuzhishan minipigs successfully resuscitated after 8 min of untreated ventricular fibrillation. Cerebral samples were collected at 24 and 72 h following return of spontaneous circulation (ROSC). We found that mitochondrial malondialdehyde and protein carbonyl levels were significantly increased in the cerebral cortex in normothermic pigs even at 24 h after ROSC, whereas mild hypothermia attenuated this increase. Moreover, mild hypothermia attenuated the decrease in Complex I and Complex III (i.e., major sites of reactive oxygen species production) activities of the mitochondrial respiratory chain and increased antioxidant enzyme manganese superoxide dismutase (MnSOD) activity. This increase in MnSOD activity was consistent with the upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA and protein expressions, and with the increase of Nrf2 nuclear translocation in normothermic pigs at 24 and 72 h following ROSC, whereas mild hypothermia enhanced these tendencies. Thus, our findings indicate that mild hypothermia attenuates mitochondrial oxidative stress in the cerebral cortex, which may be associated with reduced impairment of mitochondrial respiratory chain enzymes, and enhancement of MnSOD activity and expression via Nrf2 activation.

Therapeutic hypothermia after cardiac arrest: experience at an academically affiliated community-based veterans affairs medical center

At laboratory and clinical levels, therapeutic hypothermia has been shown to improve neurologic outcomes and mortality following cardiac arrest. We reviewed each cardiac arrest in our community-based Veterans Affairs Medical Center over a three-year period. The majority of cases were in-hospital arrests associated with initial pulseless electrical activity or asystole. Of a total of 100 patients suffering 118 cardiac arrests, 29 arrests involved comatose survivors, with eight patients completing therapeutic cooling. Cerebral performance category scores at discharge and six months were significantly better in the cooled cohort versus the noncooled cohort, and, in every case except for one, cooling was offered for appropriate reasons. Mean time to initiation of cooling protocol was 3.7 hours and mean time to goal temperature of 33°C was 8.8 hours, and few complications clearly related to cooling were noted in our case series. While in-patient hospital mortality of cardiac arrest was high at 65% mortality during hospital admission, therapeutic hypothermia was safe and feasible at our center. Our cooling times and incidence of favorable outcomes are comparable to previously published reports. This study demonstrates the feasibility of implementing, a cooling protocol a community setting, and the role of neurologists in ensuring effective hospital-wide implementation.

Mechanisms of hypothermic neuroprotection

There is now compelling clinical evidence that prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death can reduce subsequent neuronal loss and improve behavioral recovery in term infants and adults after cardiac arrest. Perhaps surprisingly, the specific mechanisms of hypothermic neuroprotection remain unclear, at least in part because hypothermia suppresses a broad range of potential injurious factors. In the present review we critically examine proposed mechanisms in relation to the known window of opportunity for effective protection with hypothermia. Better knowledge of the mechanisms of hypothermia is critical to help guide the rational development of future combination treatments to augment neuroprotection with hypothermia, and to identify those most likely to benefit from it.

Bench-to-bedside review: Hypothermia in traumatic brain injury

Traumatic brain injury remains a major cause of death and severe disability throughout the world. Traumatic brain injury leads to 1,000,000 hospital admissions per annum throughout the European Union. It causes the majority of the 50,000 deaths from road traffic accidents and leaves 10,000 patients severely handicapped: three quarters of these victims are young people. Therapeutic hypothermia has been shown to improve outcome after cardiac arrest, and consequently the European Resuscitation Council and American Heart Association guidelines recommend the use of hypothermia in these patients. Hypothermia is also thought to improve neurological outcome after neonatal birth asphyxia. Cardiac arrest and neonatal asphyxia patient populations present to health care services rapidly and without posing a diagnostic dilemma; therefore, therapeutic systemic hypothermia may be implemented relatively quickly. As a result, hypothermia in these two populations is similar to the laboratory models wherein systemic therapeutic hypothermia is commenced very soon after the injury and has shown so much promise. The need for resuscitation and computerised tomography imaging to confirm the diagnosis in patients with traumatic brain injury is a factor that delays intervention with temperature reduction strategies. Treatments in traumatic brain injury have traditionally focussed on restoring and maintaining adequate brain perfusion, surgically evacuating large haematomas where necessary, and preventing or promptly treating oedema. Brain swelling can be monitored by measuring intracranial pressure (ICP), and in most centres ICP is used to guide treatments and to monitor their success. There is an absence of evidence for the five commonly used treatments for raised ICP and all are potential 'double-edged swords' with significant disadvantages. The use of hypothermia in patients with traumatic brain injury may have beneficial effects in both ICP reduction and possible neuro-protection. This review will focus on the bench-to-bedside evidence that has supported the development of the Eurotherm3235Trial protocol.

Rapid induction of therapeutic hypothermia using convective-immersion surface cooling: safety, efficacy and outcomes

Therapeutic hypothermia has become an accepted part of post-resuscitation care. Efforts to shorten the time from return of spontaneous circulation to target temperature have led to the exploration of different cooling techniques. Convective-immersion uses a continuous shower of 2 degrees C water to rapidly induce hypothermia. The primary purpose of this multi-center trial was to evaluate the feasibility and speed of convective-immersion cooling in the clinical environment. The secondary goal was to examine the impact of rapid hypothermia induction on patient outcome. 24 post-cardiac arrest patients from 3 centers were enrolled in the study; 22 agreed to participate until the 6-month evaluations were completed. The median rate of cooling was 3.0 degrees C/h. Cooling times were shorter than reported in previous studies. The median time to cool the patients to target temperature (<34 degrees C) was 37 min (range 14-81 min); and only 27 min in a subset of patients sedated with propofol. Survival was excellent, with 68% surviving to 6 months; 87% of survivors were living independently at 6 months. Conductive-immersion surface cooling using the ThermoSuit System is a rapid, effective method of inducing therapeutic hypothermia. Although the study was not designed to demonstrate impact on outcomes, survival and neurologic function were superior to those previously reported, suggesting comparative studies should be undertaken. Shortening the delay from return of spontaneous circulation to hypothermic target temperature may significantly improve survival and neurologic outcome and warrants further study.

Moderate hypothermia suppresses jugular venous superoxide anion radical, oxidative stress, early inflammation, and endothelial injury in forebrain ischemia/reperfusion rats

The aim of this study was to assess the effect of moderate hypothermia (MH) on generation of jugular venous superoxide radical (O2-.), oxidative stress, early inflammation, and endothelial injury in forebrain ischemia/reperfusion (FBI/R) rats. Twenty-one Wistar rats were allocated to a control group (n=7, 37 degrees C), a pre-MH group (n=7, 32 degrees C before ischemia), and a post-MH group (n=7, 32 degrees C after reperfusion). MH was induced before induction of ischemia in the pre-MH group and just after reperfusion in the post-MH group. Forebrain ischemia was induced by occlusion of bilateral common carotid arteries with hemorrhagic hypotension for 10 min, followed by reperfusion. O(2)(-)(.) in the jugular vein was measured from the produced current using a novel O2-. sensor. The O2-. current showed a gradual increase during forebrain ischemia in the control and post-MH groups but was attenuated in the pre-MH group. Following reperfusion, the current showed a marked increase in the control group but was strongly attenuated in the pre- and post-MH groups. Concentrations of malondialdehyde, high-mobility group box 1 (HMGB1) protein, and intercellular adhesion molecule-1 (ICAM-1) in the brain and plasma 120 min after reperfusion in the pre- and post-MH groups were significantly lower than those in the control group, except for plasma HMGB1 in the post-MH group. In conclusion, MH suppressed O2-. measured in the jugular vein, oxidative stress, early inflammation, and endothelial injury in FBI/R rats.

Protection in animal models of brain and spinal cord injury with mild to moderate hypothermia

For the past 20 years, various laboratories throughout the world have shown that mild to moderate levels of hypothermia lead to neuroprotection and improved functional outcome in various models of brain and spinal cord injury (SCI). Although the potential neuroprotective effects of profound hypothermia during and following central nervous system (CNS) injury have long been recognized, more recent studies have described clinically feasible strategies for protecting the brain and spinal cord using hypothermia following a variety of CNS insults. In some cases, only a one or two degree decrease in brain or core temperature can be effective in protecting the CNS from injury. Alternatively, raising brain temperature only a couple of degrees above normothermia levels worsens outcome in a variety of injury models. Based on these data, resurgence has occurred in the potential use of therapeutic hypothermia in experimental and clinical settings. The study of therapeutic hypothermia is now an international area of investigation with scientists and clinicians from every part of the world contributing to this important, promising therapeutic intervention. This paper reviews the experimental data obtained in animal models of brain and SCI demonstrating the benefits of mild to moderate hypothermia. These studies have provided critical data for the translation of this therapy to the clinical arena. The mechanisms underlying the beneficial effects of mild hypothermia are also summarized.

Protection and repair of the injured spinal cord: a review of completed, ongoing, and planned clinical trials for acute spinal cord injury

Over the past 2 decades, advances in understanding the pathophysiology of spinal cord injury (SCI) have stimulated the recent emergence of several therapeutic strategies that are being examined in Phase I/II clinical trials. Ten randomized controlled trials examining methylprednisolone sodium succinate, tirilizad mesylate, monosialotetrahexosylganglioside, thyrotropin releasing hormone, gacyclidine, naloxone, and nimodipine have been completed. Although the primary outcomes in these trials were laregely negative, a secondary analysis of the North American Spinal Cord Injury Study II demonstrated that when administered within 8 hours of injury, methylprednisolone sodium succinate was associated with modest clinical benefits, which need to be weighed against potential complications. Thyrotropin releasing hormone (Phase II trial) and monosialotetrahexosylganglioside (Phase II and III trials) also showed some promise, but we are unaware of plans for future trials with these agents. These studies have, however, yielded many insights into the conduct of clinical trials for SCI. Several current or planned clinical trials are exploring interventions such as early surgical decompression (Surgical Treatment of Acute Spinal Cord Injury Study) and electrical field stimulation, neuroprotective strategies such as riluzole and minocycline, the inactivation of myelin inhibition by blocking Nogo and Rho, and the transplantation of various cellular substrates into the injured cord. Unfortunately, some experimental and poorly characterized SCI therapies are being offered outside a formal investigational structure, which will yield findings of limited scientific value and risk harm to patients with SCI who are understandably desperate for any intervention that might improve their function. Taken together, recent advances suggest that optimism for patients and clinicians alike is justified, as there is real hope that several safe and effective therapies for SCI may become available over the next decade.

The effect of hypothermia on neuronal viability following cardiopulmonary bypass and circulatory arrest in newborn piglets

OBJECTIVE

To determine the effect of recovery with mild hypothermia after cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) on the activity of selected key proteins involved in initiation (Bax, Caspase-3) or inhibition of apoptotic injury (Bcl-2, increased ratio Bcl-2/Bax) in the brain of newborn piglets.

METHODS

The piglets were placed on CPB, cooled with pH-stat management to 18 degrees C, subjected to 30 min of DHCA followed by 1h of low flow at 20 ml/kg/min, rewarmed to 37 degrees C (normothermia) or to 33 degrees C (hypothermia), separated from CPB, and monitored for 6h. Expression of above proteins was measured in striatum, hippocampus and frontal cortex by Western blots. The results are mean for six experiments+/-SEM.

RESULTS

There were no significant differences in Bcl-2 level between normothermic and hypothermic groups. The Bax levels in normothermic group in cortex, hippocampus and striatum were 94+/-9, 136+/-22 and 125+/-34 and decreased in the hypothermic group to 59+/-17 (p=0.028), 70+/-6 (p=0.002) and 48+/-8 (p=0.01). In cortex, hippocampus and striatum Bcl-2/Bax ratio increased from 1.23, 0.79 and 0.88 in normothermia to 1.96, 1.28 and 2.92 in hypothermia. Expression of Caspase-3 was 245+/-39, 202+/-74 and 244+/-31 in cortex, hippocampus and striatum in the normothermic group and this decreased to 146+/-24 (p=0.018), 44+/-16 (p=7 x 10(-7)) and 81+/-16 (p=0.01) in the hypothermic group.

CONCLUSION

In neonatal piglet model of cardiopulmonary bypass with circulatory arrest, mild hypothermia during post bypass recovery provides significant protection from cellular apoptosis, as indicated by lower expression of Bax and Caspase-3 and an increased Bcl-2/Bax ratio. The biggest protection was observed in striatum probably by decreasing of neurotoxicity of striatal dopamine.

Therapeutic hypothermia preserves antioxidant defenses after severe traumatic brain injury in infants and children

OBJECTIVE

Oxidative stress contributes to secondary damage after traumatic brain injury (TBI). Hypothermia decreases endogenous antioxidant consumption and lipid peroxidation after experimental cerebral injury. Our objective was to determine the effect of therapeutic hypothermia on oxidative damage after severe TBI in infants and children randomized to moderate hypothermia vs. normothermia.

DESIGN

Prospective randomized controlled study.

SETTING

Pediatric intensive care unit of Pittsburgh Children's Hospital.

PATIENTS

The study included 28 patients.

MEASUREMENTS AND MAIN RESULTS

We compared the effects of hypothermia (32 degrees C-33 degrees C) vs. normothermia in patients treated in a single center involved in a multicentered randomized controlled trial of hypothermia in severe pediatric TBI (Glasgow Coma Scale score

CONCLUSION

To our knowledge, this is the first study demonstrating that hypothermia attenuates oxidative stress after severe TBI in infants and children. Our data also support the concept that CSF represents a valuable tool for monitoring treatment effects on oxidative stress after TBI.

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Key Words Collapse

MESH Headings

• Antioxidants/metabolism
• Brain Injuries/metabolism
• Brain Injuries/therapy
• Child
• Child, Preschool
• Female
• Humans
• Hypothermia, Induced
• Infant
• Male
• Oxidative Stress
• Prospective Studies

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Grants

• NS061817 NINDS NIH HHS
• HD057587 NICHD NIH HHS
• P50 NS030318 NINDS NIH HHS
• R01 NS061817 NINDS NIH HHS
• T32-HD40686 NICHD NIH HHS
• U01 NS052478 NINDS NIH HHS
• T32 HD040686 NICHD NIH HHS
• R01 NS038087 NINDS NIH HHS
• NS34884 NINDS NIH HHS
• NS052478 NINDS NIH HHS
• NS30318 NINDS NIH HHS
• P01 NS030318 NINDS NIH HHS
• NS38087 NINDS NIH HHS
• R21 HD057587 NICHD NIH HHS

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Affiliation(s)

Hülya Bayir Safar Center for Resuscitation Research, Children's Hospital of Pittsburgh, Pittsburgh, PA, USA
P David Adelson
Stephen R Wisniewski
Paul Shore
YiChen Lai
Danielle Brown
Keri L Janesko-Feldman
Valerian E Kagan
Patrick M Kochanek

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Collaborators Collapse

Hypothermia for spinal cord injury

BACKGROUND CONTEXT

Interest in systemic and local hypothermia extends back over many decades, and both have been investigated as potential neuroprotective interventions in a number of clinical settings, including traumatic brain injury, stroke, cardiac arrest, and both intracranial and thoracoabdominal aortic aneurysm surgery. The recent use of systemic hypothermia in an injured National Football League football player has focused a great deal of attention on the potential use of hypothermia in acute spinal cord injury.

PURPOSE

To provide spinal clinicians with an overview of the biological rationale for using hypothermia, the past studies and current clinical applications of hypothermia, and the basic science studies and clinical reports of the use of hypothermia in acute traumatic spinal cord injury.

STUDY DESIGN/SETTING

A review of the English literature on hypothermia was performed, starting with the original clinical description of the use of systemic hypothermia in 1940. Pertinent basic science and clinical articles were identified using PubMed and the bibliographies of the articles.

METHODS

Each article was reviewed to provide a concise description of hypothermia's biological rationale, current clinical applications, complications, and experience as a neuroprotective intervention in spinal cord injury.

RESULTS

Hypothermia has a multitude of physiologic effects. From a neuroprotective standpoint, hypothermia slows basic enzymatic activity, reduces the cell's energy requirements, and thus maintains Adenosine Triphosphate (ATP) concentrations. As such, systemic hypothermia has been shown to be neuroprotective in patients after cardiac arrest, although its benefit in other clinical settings such as traumatic brain injury, stroke, and intracranial aneurysm surgery has not been demonstrated. Animal studies of local and systemic hypothermia in traumatic spinal cord injury models have produced mixed results. Local hypothermia was actively studied in the 1970s in human acute traumatic spinal cord injury, but no case series of this intervention has been published since 1984. No peer-reviewed clinical literature could be found, which describes the application of systemic hypothermia in acute traumatic spinal cord injury.

CONCLUSIONS

Animal studies of acute traumatic spinal cord injury have not revealed a consistent neuroprotective benefit to either systemic or local hypothermia. Human studies of local hypothermia after acute traumatic spinal cord injury have not been published for over two decades. No peer-reviewed studies describing the use of systemic hypothermia in this setting could be found. Although a cogent biological rationale may exist for the use of local or systemic hypothermia in acute traumatic spinal cord injury, there is little scientific literature currently available to substantiate the clinical use of either in human patients.

Postischemic mild hypothermia alleviates hearing loss because of transient ischemia

The effect of postischemic mild hypothermia on the inner ear has not been clarified. In this study, we investigated whether hypothermia after transient ischemia could prevent cochlear damage and its therapeutic time window. Mongolian gerbils were divided into six groups: a sham-operation group, a normothermia group, and four hypothermia groups in which hypothermia was induced 1-7, 1-4, 3-6, and 6-9 h after reperfusion. Animals subjected to postischemic mild hypothermia within 3 h after reperfusion had attenuated hearing loss and inner hair cell loss. The protective effect was greater when hypothermia was induced earlier and had a longer duration. This implies that mild hypothermia after ischemia could have therapeutic effects for inner ear ischemic damage.

Devices for rapid induction of hypothermia

In industrial countries it is estimated that the incidence of out-of-hospital sudden cardiac arrest lies between 36 and 128 per 100,000 inhabitants per year. Almost 80% of patients who initially survive a cardiac arrest present with coma lasting more than 1 h. Current therapy during cardiac arrest concentrates on the external support of circulation and respiration with additional drug and electrical therapy. Therapeutic hypothermia provides a new and very effective therapy for neuroprotection in patients after cardiac arrest. It is critical that mild hypothermia has to be applied very early after the ischaemic insult to be effective, otherwise the beneficial effects would be diminished or even abrogated. There are numerous methods available for cooling patients after ischaemic states. Surface cooling devices are non-invasive and range from simple ice packs to sophisticated machines with automatic feedback control. Other non-invasive methods include drugs and cold liquid ventilation. The newer devices have cooling rates comparable to invasive catheter techniques. Invasive cooling methods include the administration of ice-cold fluids intravenously, the use of intravascular cooling catheters, body cavity lavage, extra-corporeal circuits and selective brain cooling. Most of these methods are quite invasive and are still in an experimental stage. The optimal timing and technique for the induction of hypothermia after cardiac arrest have not yet been defined, and it is currently a major topic of ongoing research. The induction of hypothermia after cardiac arrest needs to be an integral component of the initial evaluation and stabilization of the patient.

Hypothermia therapy for cardiac arrest in pediatric patients

Cardiac arrest is associated with high morbidity and mortality in children. Hypothermia therapy has theoretical benefits on brain preservation and has the potential to decrease morbidity and mortality in children following cardiac arrest. The American Heart Association guidelines recommend that it should be considered in children after cardiac arrest. Methods of inducing hypothermia include simple surface cooling techniques, intravenous boluses of cold saline, gastric lavage with ice-cold normal saline, and using the temperature control device with extracorporeal life support. We recommend further study before a strong recommendation can be made to use hypothermia therapy in children with cardiac arrest.

Use of induced hypothermia for neuroprotection: indications and application

Therapeutic temperature regulation has become an exciting field of interest. Mild-to-moderate hypothermia is a safe and feasible management strategy for neuroprotection and control of intracranial pressure in neurological catastrophies such as traumatic brain injury, subarachnoid and intracerebral hemorrhage, and large hemispheric stroke. Fever is associated with worse neurological outcome in patients with brain injury, normothermia may be of benefit in this patient population. The efficacy of mild-to-moderate hypothermia has been proven for neuroprotection after cardiac arrest with ventricular fibrillation as initial rhythm, and after neonatal asphyxia. Application of hypothermia and fever control in neurocritical care, available cooling technologies and systemic effects and complications of hypothermia will be discussed.