Effects of hypothermia on intracranial pressure and brain edema formation: studies in a rat acute subdural hematoma model

Acute subdural haematoma exacerbates cerebral blood flow disorder and promotes the development of intraoperative brain bulge in patients with severe traumatic brain injury

BACKGROUND

Decompressive craniectomy (DC) is a routine procedure used for the treatment of severe traumatic brain injury (TBI) with concomitant acute subdural haematoma (SDH). However, certain patients are prone to developing malignant brain bulge during DC, which prolongs the operative time and worsens patient outcomes. Previous studies have shown that malignant intraoperative brain bulge (IOBB) may be associated with excessive arterial hyperaemia caused by cerebrovascular system disorders. Through a clinical retrospective analysis and prospective observations, we found that the cerebral blood flow of patients who possessed risk factors manifested high resistance and low flow velocity, which severely affected brain tissue perfusion and resulted in the occurrence of malignant IOBB. In the current literature, rat models of severe brain injury-associated brain bulge have rarely been reported.

METHODS

To gain an in-depth understanding of cerebrovascular changes and the cascade of responses related to brain bulge, we introduced acute SDH into the Marmarou model for the preparation of a rat model of high intracranial pressure (ICP) to simulate the pathological conditions experienced by patients with severe brain injury.

RESULTS

With the introduction of a 400-µL haematoma, significant dynamic changes occurred in ICP, mean arterial pressure, and relative blood perfusion rate of the cerebral cortical vessels. ICP increased to 56.9 ± 2.3 mmHg, mean arterial pressure showed reactive decrease, and the blood flow of cerebral cortical arteries and veins on the non-SDH-affected side decreased to < 10%. These changes could not fully recover even after DC. This resulted in generalised damage to the neurovascular unit and a lag effect to the venous blood reflux, which triggered malignant IOBB formation during DC.

CONCLUSION

An excessive increase in ICP causes cerebrovascular dysfunction and brings about a cascade of damage to brain tissue, which forms the basis for the development of diffuse brain swelling. The subsequent heterogeneous responses of the cerebral arteries and veins during craniotomy may be the main cause of primary IOBB. Clinicians should pay particular attention to the redistribution of CBF to various vessels when performing DC in patients with severe TBI.

Cerebral Blood Flow Disorder in Acute Subdural Hematoma and Acute Intraoperative Brain Bulge

Context

Acute subdural hematoma (ASDH) has a high incidence and high mortality. During surgery for ASDH, brain tissue sometimes rapidly swells and protrudes into the bone window during or after removal of the hematoma. This phenomenon, known as acute intraoperative brain bulge, progresses rapidly and can cause ischemic necrosis of brain tissue or even mortality. The mechanism of this phenomenon remains unclear.

Objective

To investigate the changes in cerebral surface blood flow during ASDH and acute intraoperative brain bulge in rats.

Methods

Adult male Sprague–Dawley rats were selected to establish an ASDH model, and acute intraoperative brain bulge was induced by late-onset intracranial hematoma. The changes in cerebral surface blood flow during ASDH and acute intraoperative brain bulge were observed with a laser speckle imaging system, and intracranial pressure (ICP) was monitored.

Results

ICP in rats increased significantly after ASDH (P < 0.05). The blood perfusion rate (BPR) values of the superior sagittal sinus, collateral vein and artery decreased significantly in rats with subdural hematomas (P < 0.05). There was no significant difference between the preoperative and 90-min postoperative BPR values of rats. ICP was significantly increased in rats with acute intraoperative brain bulge (P < 0.05) and decreased significantly after the removal of delayed hematomas (P < 0.05). The BPR of the superior sagittal sinus, collateral vein and artery decreased significantly during brain bulge (P < 0.05). After the removal of delayed hematomas, BPR increased significantly, but it remained significantly different from the values measured before brain bulge (P < 0.05).

Conclusion

ASDH may cause not only high intracranial pressure but also cerebral blood circulation disorders. Brain bulge resulting from late-onset intracranial hematoma may aggravate these circulation disorders. If the cause of brain bulge in a given patient is late-onset intracranial hematoma, clinicians should promptly perform surgery to remove the hematoma and relieve circulation disorders, thus preventing more serious complications.

Subdural hematoma decompression model: A model of traumatic brain injury with ischemic-reperfusional pathophysiology: A review of the literature

The prognosis for patients with traumatic brain injury (TBI) with subdural hematoma (SDH) remains poor. In accordance with an increasing elderly population, the incidence of geriatric TBI with SDH is rising. An important contributor to the neurological injury associated with SDH is the ischemic damage which is caused by raised intracranial pressure (ICP) producing impaired cerebral perfusion. To control intracranial hypertension, the current management consists of hematoma evacuation with or without decompressive craniotomy. This removal of the SDH results in the immediate reversal of global ischemia accompanied by an abrupt reduction of mass lesion and an ensuing reperfusion injury. Experimental models can play a critical role in improving our understanding of the underlying pathophysiology and in exploring potential treatments for patients with SDH. In this review, we describe the epidemiology, pathophysiology and clinical background of SDH.

Microdialysis as Clinical Evaluation of Therapeutic Hypothermia in Rat Subdural Hematoma Model

Cerebral microdialysis (MD) is a fine laboratory technique which has been established for studying physiological, pharmacological, and pathological changes in the experimental studies of traumatic brain injury (TBI). This technique has also been well translated and widely applied to clinical bedside monitoring to provide pathophysiological analysis in severe TBI patients. The MD technique is thus well suited for straightforward translation from basic science to clinical application.In this chapter, we describe our evaluation of MD method in acute subdural hematoma (ASDH) rat model. With 100 kDa cut-off microdialysis membrane, we could measure several biomarkers such as ubiquitin carboxy hydrolase L1 (UCH-L1), a neuronal marker and glial fibrillary acidic protein (GFAP), and a glial marker in extracellular fluid. In this experiment, we could detect that the peak of extracellular UCH-L1 in the early hypothermia group was significantly lower than in the normothermia group. Also, in the late phase of reperfusion (>2.5 h after decompression), extracellular GFAP in the early hypothermia group was lower than in the normothermia. These data thus suggested that early, preoperatively induced hypothermia could mediate the reduction of neuronal and glial damage in the reperfusion phase of ischemia/reperfusion brain injury.Microdialysis allows for the direct measurement of extracellular molecules in an attempt to characterize metabolic derangements before they become clinically relevant. Advancements in technology have allowed for the bedside assay of multiple markers of ischemia and metabolic dysfunction, and the applications for traumatic brain injury have been well established. As clinicians become more comfortable with these tools their widespread use and potential for clinical impact with continue to rise.

Preconditioning for traumatic brain injury

Traumatic brain injury (TBI) treatment is now focused on the prevention of primary injury and reduction of secondary injury. However, no single effective treatment is available as yet for the mitigation of traumatic brain damage in humans. Both chemical and environmental stresses applied before injury have been shown to induce consequent protection against post-TBI neuronal death. This concept termed "preconditioning" is achieved by exposure to different pre-injury stressors to achieve the induction of "tolerance" to the effect of the TBI. However, the precise mechanisms underlying this "tolerance" phenomenon are not fully understood in TBI, and therefore even less information is available about possible indications in clinical TBI patients. In this review, we will summarize TBI pathophysiology, and discuss existing animal studies demonstrating the efficacy of preconditioning in diffuse and focal type of TBI. We will also review other non-TBI preconditioning studies, including ischemic, environmental, and chemical preconditioning, which maybe relevant to TBI. To date, no clinical studies exist in this field, and we speculate on possible future clinical situations, in which pre-TBI preconditioning could be considered.

Neuroprotective effect of preoperatively induced mild hypothermia as determined by biomarkers and histopathological estimation in a rat subdural hematoma decompression model

OBJECT

In patients who have sustained a traumatic brain injury (TBI), hypothermia therapy has not shown efficacy in multicenter clinical trials. Armed with the post hoc data from the latest clinical trial (National Acute Brain Injury Study: Hypothermia II), the authors hypothesized that hypothermia may be beneficial in an acute subdural hematoma (SDH) rat model by blunting the effects of ischemia/reperfusion injury. The major aim of this study was to test the efficacy of temperature management in reducing brain damage after acute SDH.

METHODS

The rats were induced with acute SDH and placed into 1 of 4 groups: 1) normothermia group (37°C); 2) early hypothermia group, head and body temperature reduced to 33°C 30 minutes prior to craniotomy; 3) late hypothermia group, temperature lowered to 33°C 30 minutes after decompression; and 4) sham group, no acute SDH (only craniotomy with normothermia). To assess for neuronal and glial cell damage, the authors analyzed microdialysate concentrations of GFAP and ubiquitin carboxyl-terminal hydrolase-L1 (UCH-L1) by using a 100-kD probe. Fluoro-Jade B-positive neurons and injury volume with 2,3,5-triphenyltetrazolium chloride staining were also measured.

RESULTS

In the early phase of reperfusion (30 minutes, 2.5 hours after decompression), extracellular UCH-L1 in the early hypothermia group was significantly lower than in the normothermia group (early, 4.9 ± 1.0 ng/dl; late, 35.2 ± 12.1 ng/dl; normothermia, 50.20 ± 28.3 ng/dl; sham, 3.1 ± 1.3 ng/dl; early vs normothermia, p < 0.01; sham vs normothermia, p < 0.01, analyzed using ANOVA followed by a post hoc Bonferroni test). In the late phase of reperfusion (> 2.5 hours after decompression), extracellular GFAP in the early hypothermia group was also lower than in the normothermia and late hypothermia groups (early, 5.5 ± 2.9 ng/dl; late, 7.4 ± 3.4 ng/dl; normothermia, 15.3 ± 8.4 ng/dl; sham, 3.3 ± 1.0 ng/dl; normothermia vs sham; p < 0.01). The number of Fluoro-Jade B-positive cells in the early hypothermia group was significantly smaller than that in the normothermia group (normothermia vs early: 774,588 ± 162,173 vs 180,903 ± 42,212, p < 0.05). Also, the injury area and volume were smaller in the early hypothermia group in which hypothermia was induced before craniotomy and cerebral reperfusion (early, 115.2 ± 15.4 mm(3); late, 344.7 ± 29.1 mm(3); normothermia, 311.2 ± 79.2 mm(3); p < 0.05).

CONCLUSIONS

The data suggest that early, preoperatively induced hypothermia could mediate the reduction of neuronal and glial damage in the reperfusion phase of ischemia/reperfusion brain injury.

Combination of temperature-sensitive stem cells and mild hypothermia: a new potential therapy for severe traumatic brain injury

Stem cell transplantation holds great potential for the treatment of traumatic brain injury (TBI). However, the micro-environment of reduced oxygen and accumulated toxins leads to low survival rates of grafted cells, which dramatically limits their clinical application. Mild hypothermia has been demonstrated to improve the micro-environment after severe TBI. Thus, we speculate that combinational therapy of mild hypothermia may promote survival of grafted cells, especially temperature-sensitive stem cells, which show the most activity in mild temperatures. In this study, we first isolated mesenchymal stem cells from umbilical cord (UCSMCs) and generated the temperature-sensitive UCSMCs (tsUCSMCs) by infection with a retrovirus carrying the temperature-sensitive tsA58 SV40 LT antigen gene. We demonstrated that tsUCSMCs grew and proliferated with more activity at 33°C than at 37°C by counting cell numbers with a hematocytometer, measuring the cell cycle with flow cytometry, and detecting proliferating cell nuclear antigen (PCNA) with immunofluorescence staining. Thereafter, we established the rat severe TBI model by fluid percussion, and injected PBS, UCSMCs, or tsUCSMCs into the injured region, and subject the animals to normothermia or mild hypothermia (33°C). We found that, compared with UCSMC or tsUCSMC treatment alone, their combination with hypothermia could significantly improve motor and cognitive function with more survival of the grafted cells. Furthermore, we observed that combined therapy with hypothermia and tsUCSMCs exerted the most protective effect on the recovery of neurological function of all the tested treatments, with the highest survival and proliferation rates, and the lowest apoptosis rate. Thus this may represent a new therapeutic strategy for the treatment of severe TBI.

Effects of hypothermia on cerebral autoregulatory vascular responses in two rodent models of traumatic brain injury

Traumatic brain injury (TBI) can trigger disturbances of cerebral pressure autoregulation that can translate into the generation of secondary insults and increased morbidity/mortality. Few therapies have been developed to attenuate the damaging consequences of disturbed autoregulatory control, although some suggest that hypothermia may exert such protection. Here we reexamine this issue of traumatically induced autoregulatory disturbances and their modulation by hypothermic intervention, examining these phenomena in two different models of TBI. Adult rats were subjected to either impact acceleration injury (IAI) or lateral fluid percussion injury (LFPI) followed by the insertion of cranial windows to assess the pial arteriolar cerebral autoregulatory vascular response to the post-traumatic induction of sequential reductions of arterial blood pressure. The potential for continued pial vasodilation in response to declining blood pressure was directly measured post-injury and compared with that in injured groups subjected to 33° C of hypothermia of 1-2 h duration initiated 1 h post-injury. We observed that the TBI resulted in either impaired or abolished cerebral vascular dilation in response to the sequential declines in blood pressure. Following IAI there was a 50% reduction in the vasculature's ability to dilate in response to the induced hypotension. In contrast, following LFPI, the vascular response to hypotension was abolished both ipsilateral and contralateral to the LFPI. In animals sustaining IAI, the use of 1 h post-traumatic hypothermia preserved vascular dilation in response to declines in blood pressure in contrast to the LFPI in which the use of the same strategy afforded no improvement. However, with LFPI, the use of 2 h of hypothermia provided partial vascular protection. These results clearly illustrate that TBI can alter the cerebral autoregulatory vascular response to sequentially induced hypotensive insult, whereas the use of post-traumatic hypothermia provides benefit. Collectively, these studies also demonstrate that different animal models of TBI can evoke different biological responses to injury.

[Intensive care management [corrected] of patients with intracerebral hemorrhage]

Approximately 10-15% of acute strokes are caused by non-aneurysmatic intracerebral hemorrhage (ICH) and incidences are expected to increase due to an aging population. Studies from the 1990s estimated mortality of ICH to be as high as 50%. However, these figures may partly be attributed to the fact that patients suffering from ICH frequently received only supportive therapy and the poor prognosis may therefore be more a self-fulfilling prophecy. Recently it has been shown that treatment in a specialized neurological intensive care unit alone was associated with better outcomes after ICH. In recent years considerable efforts have been undertaken in order to develop new therapies for ICH and to assess them in randomized controlled trials. Apart from admission status, hemorrhage volume is considered to be the main prognostic factor and impeding the spread of the hematoma is thus a basic therapeutic principle. The use of activated factor VIIa (aFVIIa) to stop hematoma enlargement has been assessed in two large randomized controlled trials, however the promising results of the dose-finding study could not be confirmed in a phase III trial. Although hemostatic therapy with aFVIIa reduced growth of the hematoma it failed to improve clinical outcome. Similar results were found in a randomized controlled trial on blood pressure management in acute ICH. The link between reduction of hematoma growth and improved outcome is therefore still lacking. Likewise the value of surgical hematoma evacuation remains uncertain. In the largest randomized controlled trial on surgical treatment in ICH so far, only a small subgroup of patients with superficial hemorrhages seemed to benefit from hematoma evacuation. Whether improved intensive care can contribute to improved outcome after ICH will be shown by data obtained in the coming years.

Combinational therapy using hypothermia and the immunophilin ligand FK506 to target altered pial arteriolar reactivity, axonal damage, and blood-brain barrier dysfunction after traumatic brain injury in rat

This study evaluated the utility of combinational therapy, coupling delayed posttraumatic hypothermia with delayed FK506 administration, on altered cerebral vascular reactivity, axonal injury, and blood-brain barrier (BBB) disruption seen following traumatic brain injury (TBI). Animals were injured, subjected to various combinations of hypothermic/FK506 intervention, and equipped with cranial windows to assess pial vascular reactivity to acetylcholine. Animals were then processed with antibodies to the amyloid precursor protein and immunoglobulin G to assess axonal injury and BBB disruption, respectively. Animals were assigned to five groups: (1) sham injury plus delayed FK506, (2) TBI, (3) TBI plus delayed hypothermia, (4) TBI plus delayed FK506, and (5) TBI plus delayed hypothermia with FK506. Sham injury plus FK506 had no impact on vascular reactivity, axonal injury, or BBB disruption. Traumatic brain injury induced dramatic axonal injury and altered pial vascular reactivity, while triggering local BBB disruption. Delayed hypothermia or FK506 after TBI provided limited protection. However, TBI with combinational therapy achieved significantly enhanced vascular and axonal protection, with no BBB protection. This study shows the benefits of combinational therapy, using posttraumatic hypothermia with FK506 to attenuate important features of TBI. This suggests that hypothermia not only protects but also extends the therapeutic window for improved FK506 efficacy.

The effects of selective brain hypothermia and decompressive craniectomy on brain edema after closed head injury in mice

Intractable brain edema remains one of the main causes of death after traumatic brain injury (TBI). Brain hypothermia and decompressive craniectomy have been considered as potential therapies. The goal of our experimental study was to determine if selective hypothermia in combination with craniectomy could modify the development of posttraumatic brain edema. Male CD-1 mice were anesthetized with halothane and randomly assigned into the following groups: sham-operated (n = 5), closed head injury (CHI) alone (n = 5), CHI followed by craniectomy at 1 h post-TBI (n = 5) and CHI + craniectomy and selective hypothermia (focal brain cooling using cryosurgery device) maintained for 5 h (n = 5). Animals were sacrificed at 7 h posttrauma and brains were removed, sagittally dissected and dried. The brain water content of separate hemispheres was calculated from the weight difference before and after drying. In the CHI alone group there was no significant increase in brain water content in both the ipsi- and contralateral hemispheres (80.59 +/- 1% and 78.74 +/- 0.9% in the CHI group vs. 79.31 +/- 0.7% and 79.01 +/- 0.3% in the sham group, respectively). Brain edema was significantly increased ipsilaterally in the trauma + craniectomy group (82.11 +/- 0.6%, p < 0.05), but not in the trauma + craniectomy + hypothermia group (81.52 +/- 1.1%, p > 0.05) as compared to the sham group (79.31 +/- 0.7%). These data suggest that decompressive craniectomy leads to an increase in brain water content after CHI. Additional focal hypothermia may be an effective approach in the treatment of posttraumatic brain edema.

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.

Does early medical intervention have a role in the management of intracerebral haemorrhage?

INTRODUCTION

An increasing amount of research is now being directed towards the medical treatment of patients who have suffered an intracerebral haemorrhage (ICH). Despite this, no routine drug treatment to date has been shown to be unequivocally effective in unselected patients.

TREATMENTS/DISCUSSION

Approaches to treatment are based upon our understanding of the pathophysiological sequelae following ICH. Strategies to reduce haematoma growth, subsequent oedema formation and perihaematoma ischaemia are key targets for further research. Whether these therapies become valuable tools for the future is as yet unclear. Until then, the mainstay of the medical management of ICH remains individualised care.

CONCLUSIONS

There is now a pressing need for large prospective randomised controlled trials to determine the effectiveness of pharmacological therapies for this condition.

REPRINT

Purpose— The aim of this statement is to present current and comprehensive recommendations for the diagnosis and treatment of acute spontaneous intracerebral hemorrhage.

Methods— A formal literature search of Medline was performed through the end date of August 2006. The results of this search were complemented by additional articles on related issues known to the writing committee. Data were synthesized with the use of evidence tables. The American Heart Association Stroke Council’s Levels of Evidence grading algorithm was used to grade each recommendation. Prerelease review of the draft guideline was performed by 5 expert peer reviewers and by the members of the Stroke Council Leadership Committee. It is intended that this guideline be fully updated in 3 years’ time.

Results— Evidence-based guidelines are presented for the diagnosis of intracerebral hemorrhage, the management of increased arterial blood pressure and intracranial pressure, the treatment of medical complications of intracerebral hemorrhage, and the prevention of recurrent intracerebral hemorrhage. Recent trials of recombinant factor VII to slow initial bleeding are discussed. Recommendations for various surgical approaches for treatment of spontaneous intracerebral hemorrhage are presented. Finally, withdrawal-of-care and end-of-life issues in patients with intracerebral hemorrhage are examined.

Guidelines for the Management of Spontaneous Intracerebral Hemorrhage in Adults

PURPOSE

The aim of this statement is to present current and comprehensive recommendations for the diagnosis and treatment of acute spontaneous intracerebral hemorrhage.

METHODS

A formal literature search of Medline was performed through the end date of August 2006. The results of this search were complemented by additional articles on related issues known to the writing committee. Data were synthesized with the use of evidence tables. The American Heart Association Stroke Council's Levels of Evidence grading algorithm was used to grade each recommendation. Prerelease review of the draft guideline was performed by 5 expert peer reviewers and by the members of the Stroke Council Leadership Committee. It is intended that this guideline be fully updated in 3 years' time.

RESULTS

Evidence-based guidelines are presented for the diagnosis of intracerebral hemorrhage, the management of increased arterial blood pressure and intracranial pressure, the treatment of medical complications of intracerebral hemorrhage, and the prevention of recurrent intracerebral hemorrhage. Recent trials of recombinant factor VII to slow initial bleeding are discussed. Recommendations for various surgical approaches for treatment of spontaneous intracerebral hemorrhage are presented. Finally, withdrawal-of-care and end-of-life issues in patients with intracerebral hemorrhage are examined.

[Therapeutic hypothermia]

The benefit of therapeutic hypothermia after severe head injury is highly controversial. However, hypothermia is still used and studied in this context for multiple reasons. Efficacy of hypothermia is demonstrated after cerebral ischemia in numerous animal studies and after cardiac arrest in human studies. Hyperthermia is a major independent factor of outcome after cerebral ischemic or traumatic brain injury. Moreover, ICP is related to core temperature, and hypothermia may be used to decrease intracranial hypertension. However, many questions are still unresolved and can explain discrepancies between clinical studies: direct measurement of cerebral temperature, relationship between ICP, temperature and PaCO(2), level and duration of hypothermia and precise methods for cooling and particularly for rewarming.

Effects of delayed, prolonged hypothermia on the pial vascular response after traumatic brain injury in rats

Object. In the experimental setting, hypothermia has been demonstrated to attenuate the damaging consequences of stroke and traumatic brain injury (TBI). Laboratory studies of TBI have focused primarily on the use of early hypothermic intervention, with little consideration of the potential efficacy of more delayed but prolonged hypothermia, which would constitute a more clinically relevant approach. In this investigation, the authors evaluated whether delayed, prolonged hypothermia after TBI protected the cerebral microcirculation.

Methods. Male Sprague—Dawley rats were equipped with cranial windows for direct visualization of the pial arterial circulation and then subjected to impact-acceleration brain injury. The rats were randomly divided into four experimental groups: Group 1 consisted of normothermic animals; in Group 2 the rats received a 1-hour period of hypothermia (32°C) 30 minutes posttrauma, followed by slow rewarming (32–37°C/90 minutes); and in Groups 3 and 4 the rats received a more delayed induction (at 1 hour postinjury) of either 1 hour (Group 3) or 2 hours (Group 4) of hypothermia, followed by the slow rewarming. The pial arteriolar responses to acetylcholine (ACh) or hypercapnia were measured until up to 6 hours postinjury. With this approach the authors found that the normothermic group demonstrated severely impaired vasoreactivity in terms of ACh-dependent dilation and CO2 reactivity in comparison to baseline values (p < 0.001). In contrast, hypothermia of short duration that was initiated early (30 minutes postinjury) conferred significant cerebrovascular protection (p < 0.001), yet this protection was reduced when the onset of this 1-hour hypothermic period was postponed to 1 hour postinjury. Nevertheless, reduced protection could be significantly improved (p < 0.001) with prolongation of the hypothermic period to 2 hours.

Conclusions. The results of this study show that early as well as delayed but prolonged hypothermia attenuate the impaired vascular responsiveness seen after TBI, indicating the potential clinical usefulness of this treatment.

Mild hypothermia in neurologic emergency: an update

Induced hypothermia to treat various neurologic emergencies, which had initially been introduced into clinical practice in the 1940s and 1950s, had become obsolete by the 1980s. In the early 1990s, however, it made a comeback in the treatment of severe traumatic brain injury. The success of mild hypothermia led to the broadening of its application to many other neurologic emergencies. We sought to summarize recent developments in mild hypothermia, as well as its therapeutic potential and limitations. Mild hypothermia has been applied with varying degrees of success in many neurologic emergencies, including traumatic brain injury, spinal cord injury, ischemic stroke, subarachnoid hemorrhage, out-of-hospital cardiopulmonary arrest, hepatic encephalopathy, perinatal asphyxia (hypoxic-anoxic encephalopathy), and infantile viral encephalopathy. At present, the efficacy and safety of mild hypothermia remain unproved. Although the preliminary clinical studies have shown that mild hypothermia can be a feasible and relatively safe treatment, multicenter randomized, controlled trials are warranted to define the indications for induced hypothermia in an evidence-based fashion.

Effects of mild hypothermia and alkalizing agents on brain injuries in rats with acute subdural hematomas

Brain ischemia is the leading pathopysiological mechanism in the development of secondary brain damage after acute subdural hematoma (SDH). Hypothermia has been employed as an effective cerebroprotective treatment on brain injuries, but the control of the general condition is very difficult under hypothermia, and various severe complications have been reported. Cerebral acidosis in the ischemic area is one of the important factors augmenting the brain edema formation. Tris-(hydroxymethyl)-aminomethane (THAM) has been used as an alkalizing agent for acidosis on brain injury and is reported to be effective. In the present study, we used a rat acute SDH model to assess the effect of mild (35 degrees C) hypothermia and THAM combined treatment on brain water content, brain ischemia, and blood-brain barrier (BBB) permeability at 4 h after hematoma induction. Mild hypothermia did not significantly reduce the brain water content beneath the hematoma (79.5 +/- 0.2%) compared to normothermia (80.2 +/- 0.2%), but mild hypothermia combined to THAM resulted in a significant reduction (78.7 +/- 0.0%; p < 0.01). Combined with mild hypothermia, THAM treatment significantly reduced the Evan's blue extravasation (35 +/- 7 ng/g wet tissue; p < 0.05) compared to normothermia (63 +/- 7 ng/g wet tissue). Furthermore, the volume of infarction at 24 h after the hematoma induction (54 +/- 3 mm(3); p < 0.01) was significantly smaller by the combined treatment compared with normothermia (70 +/- 2 mm(3)). The present findings indicate that mild hypothermia of 35 degrees C combined with THAM presents a potent cerebroprotective strategy. The protection of the BBB is one of the possible cerebroprotective mechanisms in this rat acute SDH model.

Moderate hypothermia in severe head injuries: the present and the future

The use of therapeutic moderate hypothermia for treating severe traumatic brain injury has been reported for more than 50 years. However, the most intense investigation of this treatment has occurred during the last 10 to 15 years. Virtually all preclinical studies have documented a robust treatment effect, not only in terms of reduced excitotoxicity and cerebral acidosis, but also in terms of histologic preservation and improved behavioral outcomes. Several single-center and small multicenter clinical trials conducted during the last decade also demonstrated benefit of early and late therapeutic hypothermia. However, a multicenter trial reported in February 2001 that included nearly 400 patients found no notable differences in neurologic outcomes in matched patients with head injuries who were treated with 48 hours of therapeutic moderate hypothermia compared with those kept at normal temperature. Findings from this study did suggest that rapid rewarming of patients with head injuries may be deleterious. A subgroup of young patients (less than 45 years of age) who were kept normovolemic showed a trend toward improved outcomes when treated with hypothermia. Current investigations, particularly in the preclinical arena, are focusing on combination therapy. To date, however, the addition of fibroblast growth factor, cyclosporine, or interleukin (IL)-10 to therapeutic moderate hypothermia has not been found to provide greater benefit than either therapy when used alone. Future investigations are aimed at further identifying the physiologic mechanisms responsible for secondary brain injury and ways in which other novel combination therapies may be expected to improve outcomes.

Ischemic preconditioning reduces infarct volume after subdural hematoma in the rat

The aim of the present study was to investigate the effects of ischemic preconditioning on infarct volume in a rat model of subdural hematoma (SDH). Ischemic preconditioning was induced by 15 min transient middle cerebral artery (MCA) occlusion followed 3 days later by the injection of 300 microl of autologous venous blood into the subdural space. Preconditioning significantly reduced the volume of cortical infarction (by 26%, P<0.001) 24 h after SDH induction, but not brain swelling (P>0.05) relative to sham-operated non-preconditioned animals. These data support the view that ischemic preconditioning reduces ischemic brain damage in this rat model of SDH.

Treatment window for hypothermia in brain injury

OBJECT

The goal of this study was to evaluate the therapeutic window for hypothermia treatment following experimental brain injury by measuring edema formation and functional outcome.

METHODS

Traumatic brain injury (TBI) was produced in anesthetized rats by using cortical impact injury. Edema was measured in the ipsilateral and contralateral hemispheres by subtracting dry weight from wet weight, and neurological function was assessed using a battery of behavioral tests 24 hours after TBI. In injured rats, it was found that brain water levels were elevated at I hour postinjury, compared with those in sham-injured control animals, and that edema peaked at 24 hours and remained elevated for 4 days. Hypothermia (3 hours at 30 degrees C) induced either immediately after TBI or 60 minutes after TBI significantly reduced early neurological deficits. Delay of treatment by 90 or 120 minutes postinjury did not result in this neurological protection. Immediate administration of hypothermia also significantly decreased the peak magnitude of edema at 24 hours and 48 hours postinjury, compared with that in normothermic injured control animals. When delayed by 90 minutes, hypothermia did not affect the pattern of edema formation.

CONCLUSIONS

When hypothermia was administered immediately or 60 minutes after TBI, injured rats showed an improvement in functional outcome and a decrease in edema. Delayed hypothermia treatment had no effect on functional outcome or on edema.