A review of selective hypothermia in the management of traumatic brain injury

Neurovascular Interventions for Neurotrauma: From Treatment of Injured Vessels to Treatment of the Injured Brain?

Traumatic brain injury is often associated with a direct or secondary neurovascular pathology. In this review, we present recent advancements in endovascular neurosurgery that enable accurate and effective vessel reconstruction with emphasis on its role in early diagnosis, the expanding use of flow diversion in pseudoaneurysms, and traumatic arteriovenous fistulas. In addition, future directions in which catheter-based interventions could potentially affect traumatic brain injury are described: targeting blood brain barrier integrity using the advantages of intra-arterial drug delivery of blood brain barrier stabilizers to prevent secondary brain edema, exploring the impact of endovascular venous access as a means to modulate venous outflow in an attempt to reduce intracranial pressure and augment brain perfusion, applying selective intra-arterial hypothermia as a neuroprotection method mitigating some of the risks conferred by systemic cooling, trans-vessel wall delivery of regenerative therapy agents, and shifting attention using multimodal neuromonitoring to post-traumatic vasospasm to further characterize the role it plays in secondary brain injury. Thus, we believe that the potential of endovascular tools can be expanded because they enable access to the "highways" governing perfusion and flow and call for further research focused on exploring these routes because it may contribute to novel endovascular approaches currently used for treating injured vessels, harnessing them for treatment of the injured brain.

Selective Brain Hypothermia in Acute Ischemic Stroke: Reperfusion Without Reperfusion Injury

In acute ischemic stroke, early recanalization of the occluded artery is crucial for best outcome to be achieved. Recanalization aims at restoring blood flow to the ischemic tissue (reperfusion) and is achieved with pharmacological thrombolytic drugs, endovascular thrombectomy (EVT) devices, or both. The introduction of modern endovascular devices has led to tremendous anatomical and clinical success with rates of substantial reperfusion exceeding 80% and proven clinical benefit in patients with anterior circulation large vessel occlusions (LVOs). However, not every successful reperfusion procedure leads to the desired clinical outcome. In fact, the rate of non-disabled outcome at 3 months with current EVT treatment is ~1 out of 4. A constraint upon better outcomes is that reperfusion, though resolving ischemic stress, may not restore the anatomic structures and metabolic functions of ischemic tissue to their baseline states. In fact, ischemia triggers a complex cascade of destructive mechanisms that can sometimes be exacerbated rather than alleviated by reperfusion therapy. Such reperfusion injury may cause infarct progression, intracranial hemorrhage, and unfavorable outcome. Therapeutic hypothermia has been shown to have a favorable impact on the molecular elaboration of ischemic injury, but systemic hypothermia is limited by slow speed of attaining target temperatures and clinical complications. A novel approach is endovascular delivery of hypothermia to cool the affected brain tissue selectively and rapidly with tight local temperature control, features not available with systemic hypothermia devices. In this perspective article, we discuss the possible benefits of adjunctive selective endovascular brain hypothermia during interventional stroke treatment.

Dynamic Thermal Mapping of Localized Therapeutic Hypothermia in the Brain

Although whole body cooling is used widely to provide therapeutic hypothermia for the brain, there are undesirable clinical side effects. Selective brain cooling may allow for rapid and controllable neuroprotection while mitigating these undesirable side effects. We evaluated an innovative cerebrospinal fluid (CSF) cooling platform that utilizes chilled saline pumped through surgically implanted intraventricular catheters to induce hypothermia. Magnetic resonance thermal imaging of the healthy sheep brain (n = 4) at 7.0T provided dynamic temperature measurements from the whole brain. Global brain temperature was 38.5 ± 0.8°C at baseline (body temperature of 39.2 ± 0.4°C), and decreased by 3.1 ± 0.3°C over ∼30 min of cooling (p < 0.0001). Significant cooling was achieved in all defined regions across both the ipsilateral and contralateral hemispheres relative to catheter placement. On cooling cessation, global brain temperature increased by 3.1 ± 0.2°C over ∼20 min (p < 0.0001). Rapid and synchronized temperature fall/rise on cooling onset/offset was observed reproducibly with rates ranging from 0.06-0.21°C/min, where rewarming was faster than cooling (p < 0.0001) signifying the importance of thermoregulation in the brain. Although core regions (including the subcortex, midbrain, olfactory tract, temporal lobe, occipital lobe, and parahippocampal cortex) had slightly warmer (∼0.2°C) baseline temperatures, after cooling, temperatures reached the same level as the non-core regions (35.6 ± 0.2°C), indicating the cooling effectiveness of the CSF-based cooling device. In summary, CSF-based intraventricular cooling reliably reduces temperature in all identified brain regions to levels known to be neuroprotective, while maintaining overall systemic normothermia. Dynamic thermal mapping provides high spatiotemporal temperature measurements that can aid in optimizing selective neuroprotective protocols.

A virtual rat for simulating environmental and exertional heat stress

Severe cases of environmental or exertional heat stress can lead to varying degrees of organ dysfunction. To understand heat-injury progression and develop efficient management and mitigation strategies, it is critical to determine the thermal response in susceptible organs under different heat-stress conditions. To this end, we used our previously published virtual rat, which is capable of computing the spatiotemporal temperature distribution in the animal, and extended it to simulate various heat-stress scenarios, including 1) different environmental conditions, 2) exertional heat stress, 3) circadian rhythm effect on the thermal response, and 4) whole body cooling. Our predictions were consistent with published in vivo temperature measurements for all cases, validating our simulations. We observed a differential thermal response in the organs, with the liver experiencing the highest temperatures for all environmental and exertional heat-stress cases. For every 3°C rise in the external temperature from 40 to 46°C, core and organ temperatures increased by ∼0.8°C. Core temperatures increased by 2.6 and 4.1°C for increases in exercise intensity from rest to 75 and 100% of maximal O2 consumption, respectively. We also found differences as large as 0.8°C in organ temperatures for the same heat stress induced at different times during the day. Even after whole body cooling at a relatively low external temperature (1°C for 20 min), average organ temperatures were still elevated by 2.3 to 2.5°C compared with normothermia. These results can be used to optimize experimental protocol designs, reduce the amount of animal experimentation, and design and test improved heat-stress prevention and management strategies.

The evidence base for nursing care and monitoring of patients during therapeutic temperature management

Therapeutic temperature management (TTM) is fast becoming a primary management strategy for a variety of medical conditions treated in critical care settings throughout the world. Nurses who provide direct care and who are tasked with developing multidisciplinary protocols and pathways are struggling to collate evidence from which to support specific nursing interventions. The aim of this project was to create the first comprehensive set of evidence-based guidelines specific to nursing care of the patient for whom TTM is medically necessary. Evidence-based nursing practice summaries are provided for nine nursing content areas: interventions to manage temperature, monitoring temperature, neurologic, cardiac, pulmonary, skin care, gastrointestinal/endocrine, laboratory findings, and general considerations for nursing care.

Current and future approaches to the therapy of human rabies

Human rabies has traditionally been considered a uniformly fatal disease. However, recent decades have seen several instances in which individuals have developed clinical signs of rabies, but survived, usually with permanent neurologic sequelae. Most of these patients had received prophylactic rabies vaccine before the onset of illness. The best outcomes have been seen in patients infected with bat viruses, which appear to be less virulent for humans than strains associated with other rabies vectors. In 2003, an article by rabies experts suggested that survival might be improved through a combination of vaccine, anti-rabies immunoglobulin, antiviral drugs and the anesthetic ketamine, which had shown benefit in an animal model. One year later, a girl in Milwaukee who developed rabies after bat exposure was treated with some of these measures, plus a drug-induced (therapeutic) coma, and survived her illness with mild neurologic sequelae. Although the positive outcome in this case has been attributed to the treatment regimen, it more likely reflects the patient's own brisk immune response, as anti-rabies virus antibodies were detected at the time of hospital admission, even though she had not been vaccinated. This conclusion is supported by the failure of the "Milwaukee Protocol" to prevent death in numerous subsequent cases. Use of this protocol should therefore be discontinued. Future research should focus on the use of animal models to improve understanding of the pathogenesis of rabies and for the development of new therapeutic approaches.

Early management of severe traumatic brain injury

Severe traumatic brain injury remains a major health-care problem worldwide. Although major progress has been made in understanding of the pathophysiology of this injury, this has not yet led to substantial improvements in outcome. In this report, we address present knowledge and its limitations, research innovations, and clinical implications. Improved outcomes for patients with severe traumatic brain injury could result from progress in pharmacological and other treatments, neural repair and regeneration, optimisation of surgical indications and techniques, and combination and individually targeted treatments. Expanded classification of traumatic brain injury and innovations in research design will underpin these advances. We are optimistic that further gains in outcome for patients with severe traumatic brain injury will be achieved in the next decade.

Brain temperature: heat production, elimination and clinical relevance

Neurological insults are a leading cause of morbidity and mortality, both in adults and especially in children. Among possible therapeutic strategies to limit clinical cerebral damage and improve outcomes, hypothermia remains a promising and beneficial approach. However, its advantages are still debated after decades of use. Studies in adults have generated conflicting results, whereas in children recent data even suggest that hypothermia may be detrimental. Is it because brain temperature physiology is not well understood and/or not applied properly, that hypothermia fails to convince clinicians of its potential benefits? Or is it because hypothermia is not, as believed, the optimal strategy to improve outcome in patients affected with an acute neurological insult? This review article should help to explain the fundamental physiological principles of brain heat production, distribution and elimination under normal conditions and discuss why hypothermia cannot yet be recommended routinely in the management of children affected with various neurological insults.

Therapy of human rabies

Preventive therapy for rabies, including wound cleansing and active and passive immunization after a recognized exposure, is highly efficacious. Unfortunately, there is no established therapy that is effective for patients who develop rabies encephalomyelitis. There have been several survivors from rabies and all but one received rabies vaccine prior to the onset of clinical illness. Aggressive approaches to therapy of human rabies may be appropriate in certain situations. There is no scientific rationale for the use of therapeutic coma, and there are many reports of failures using this approach. Therapeutic coma should be abandoned for the therapy of rabies. New approaches such as therapeutic hypothermia should be evaluated, in combination with other therapeutic agents. More basic research is needed on the mechanisms involved in rabies pathogenesis, which will hopefully facilitate the development of new therapeutic approaches in the future for this ancient disease.

Moderate increase in temperature may exacerbate neuroinflammatory processes in the brain: human cell culture studies

The effect of a moderate, physiologically relevant rise in temperature on several neuroinflammatory parameters was investigated in vitro using human cell lines and cultured human astrocytes. A two degree Celsius rise in temperature was found to enhance the neurotoxicity of microglia-like and astrocytic cells, increase the release of monocyte chemotactic protein (MCP)-1 by activated human monocytic THP-1 cells and amplify the generation of reactive oxygen intermediates by differentiated HL-60 myelocytic cells. Moderate increases in body temperature may exacerbate neuroinflammation and neuronal injury in chronic neurodegenerative disorders. Hence, therapies aimed at lowering the body temperature could be used to slow down the progression of such diseases.

Hypothermia-induced neurite outgrowth is mediated by tumor necrosis factor-alpha

Systemic or brain-selective hypothermia is a well-established method for neuroprotection after brain trauma. There is increasing evidence that hypothermia exerts beneficial effects on the brain and may also support regenerative responses after brain damage. Here, we have investigated whether hypothermia influences neurite outgrowth in vitro via modulation of the post-injury cytokine milieu. Organotypic brain slices were incubated: deep hypothermia (2 h at 17 degrees C), rewarming (2 h up to 37 degrees C), normothermia (20 h at 37 degrees C). Neurite density and cytokine release (IL 1beta, IL-6, IL-10, and TNF-alpha) were investigated after 24 h. For functional analysis mice deficient in NT-3/NT-4 and TNF-alpha as well as the TNF-alpha inhibitor etanercept were used. Hypothermia led to a significant increase of neurite outgrowth, which was independent of neurotrophin signaling. In contrast to other cytokines investigated, TNF-alpha secretion by organotypic brain slices was significantly increased after deep hypothermia. Moreover, hypothermia-induced neurite extension was abolished after administration of the TNF-alpha inhibitor and in TNF-alpha knockout mice. We demonstrate that TNF-alpha is responsible for inducing neurite outgrowth in the context of deep hypothermia and rewarming. These data suggest that hypothermia not only exerts protective effects in the CNS but may also support neurite outgrowth as a potential mechanism of regeneration.

Synergistic benefits of erythropoietin and simvastatin after traumatic brain injury

Simvastatin and recombinant human erythropoietin (rhEpo) are implicated as potential therapeutic candidates for traumatic brain injury (TBI). Prominent effects of simvastatin include its anti-inflammatory, neurotrophic and neuroregenerative actions studied in various models of neuronal injury. On the other hand, rhEpo has been shown to promote cell survival mechanisms by producing anti-apoptotic and cell proliferative actions. Beneficial effects of rhEpo and statin monotherapies have been well studied. However, there are no reports showing combined use of rhEpo and statins after TBI. This investigation examined if combined efficacy of cell proliferative ability of rhEpo along with the neuroregenerative ability of simvastatin will render maximum recovery in a controlled cortical impact (CCI) mouse model of TBI. Results showed that compared to baseline TBI, rhEpo was more effective than simvastatin in promoting cell proliferation while simvastatin was more effective than rhEpo in restoring axonal damage following TBI. Combined treatment with simvastatin and rhEpo maximally restored axonal integrity while simultaneously inducing greater proliferation of newly formed cells resulting in better functional recovery after TBI than either alone. This is the first study showing the efficacy of erythropoietin-simvastatin combinational therapeutic approach in achieving greater structural and cognitive recovery after TBI.

Mild hypothermia for refractory focal status epilepticus in an infant with hemimegalencephaly

Hypothermia can reduce seizure frequency in animal models of status epilepticus, and its effectiveness in human status epilepticus has been reported occasionally. We report an infant with hemimegalencephaly who presented with generalized status epilepticus. After high dose intravenous drug therapy, this converted to focal status epilepticus in the right occipital region. A sudden cessation of all seizure activity was found to coincide with accidental hypothermia. After application of mild continuous hypothermia, a marked reduction of seizure frequency occurred, which allowed reduction of intravenous drug doses and discharge from the IC unit. Ultimately, hemispherectomy was needed to achieve long term seizure control. The therapeutic effect of hypothermia should be further investigated in patients with refractory status epilepticus. When used in combination with anti-epileptic drugs, seizure control may be achieved at lower doses. Hypothermia may obviate the need for potentially dangerous barbiturate therapy. This case demonstrates that even a mild degree of hypothermia (+/-36 degrees C) can be remarkably effective.

Emerging treatments for traumatic brain injury

BACKGROUND

This review summarizes promising approaches for the treatment of traumatic brain injury (TBI) that are in either preclinical or clinical trials.

OBJECTIVE

The pathophysiology underlying neurological deficits after TBI is described. An overview of select therapies for TBI with neuroprotective and neurorestorative effects is presented.

METHODS

A literature review of preclinical TBI studies and clinical TBI trials related to neuroprotective and neurorestorative therapeutic approaches is provided.

RESULTS/CONCLUSION

Nearly all Phase II/III clinical trials in neuroprotection have failed to show any consistent improvement in outcome for TBI patients. The next decade will witness an increasing number of clinical trials that seek to translate preclinical research discoveries to the clinic. Promising drug- or cell-based therapeutic approaches include erythropoietin and its carbamylated form, statins, bone marrow stromal cells, stem cells singularly or in combination or with biomaterials to reduce brain injury via neuroprotection and promote brain remodeling via angiogenesis, neurogenesis, and synaptogenesis with a final goal to improve functional outcome of TBI patients. In addition, enriched environment and voluntary physical exercise show promise in promoting functional outcome after TBI, and should be evaluated alone or in combination with other treatments as therapeutic approaches for TBI.