Effects of hyperbaric oxygenation therapy on cerebral metabolism and intracranial pressure in severely brain injured patients

The use of hyperbaric oxygen for veterans with PTSD: basic physiology and current available clinical data

Post-traumatic stress disorder (PTSD) affects up to 30% of veterans returning from the combat zone. Unfortunately, a substantial proportion of them do not remit with the current available treatments and thus continue to experience long-term social, behavioral, and occupational dysfunction. Accumulating data implies that the long-standing unremitting symptoms are related to changes in brain activity and structure, mainly disruption in the frontolimbic circuit. Hence, repair of brain structure and restoration of function could be a potential aim of effective treatment. Hyperbaric oxygen therapy (HBOT) has been effective in treating disruptions of brain structure and functions such as stroke, traumatic brain injury, and fibromyalgia even years after the acute insult. These favorable HBOT brain effects may be related to recent protocols that emphasize frequent fluctuations in oxygen concentrations, which in turn contribute to gene expression alterations and metabolic changes that induce neuronal stem cell proliferation, mitochondrial multiplication, angiogenesis, and regulation of the inflammatory cascade. Recently, clinical findings have also demonstrated the beneficial effect of HBOT on veterans with treatment-resistant PTSD. Moderation of intrusive symptoms, avoidance, mood and cognitive symptoms, and hyperarousal were correlated with improved brain function and with diffusion tensor imaging-defined structural changes. This article reviews the current data on the regenerative biological effects of HBOT, and the ongoing research of its use for veterans with PTSD.

Management Strategies Based on Multi-Modality Neuromonitoring in Severe Traumatic Brain Injury

Secondary brain injury after neurotrauma is comprised of a host of distinct, potentially concurrent and interacting mechanisms that may exacerbate primary brain insult. Multimodality neuromonitoring is a method of measuring multiple aspects of the brain in order to understand the signatures of these different pathomechanisms and to detect, treat, or prevent potentially reversible secondary brain injuries. The most studied invasive parameters include intracranial pressure (ICP), cerebral perfusion pressure (CPP), autoregulatory indices, brain tissue partial oxygen tension, and tissue energy and metabolism measures such as the lactate pyruvate ratio. Understanding the local metabolic state of brain tissue in order to infer pathology and develop appropriate management strategies is an area of active investigation. Several clinical trials are underway to define the role of brain tissue oxygenation monitoring and electrocorticography in conjunction with other multimodal neuromonitoring information, including ICP and CPP monitoring. Identifying an optimal CPP to guide individualized management of blood pressure and ICP has been shown to be feasible, but definitive clinical trial evidence is still needed. Future work is still needed to define and clinically correlate patterns that emerge from integrated measurements of metabolism, pressure, flow, oxygenation, and electrophysiology. Pathophysiologic targets and precise critical care management strategies to address their underlying causes promise to mitigate secondary injuries and hold the potential to improve patient outcome. Advancements in clinical trial design are poised to establish new standards for the use of multimodality neuromonitoring to guide individualized clinical care.

Identifying the Target Traumatic Brain Injury Population for Hyperbaric Oxygen Therapy

Traumatic brain injury (TBI) results from direct penetrating and indirect non-penetrating forces that alters brain functions, affecting millions of individuals annually. Primary injury following TBI is exacerbated by secondary brain injury; foremost is the deleterious inflammatory response. One therapeutic intervention being increasingly explored for TBI is hyperbaric oxygen therapy (HBOT), which is already approved clinically for treating open wounds. HBOT consists of 100% oxygen administration, usually between 1.5 and 3 atm and has been found to increase brain oxygenation levels after hypoxia in addition to decreasing levels of inflammation, apoptosis, intracranial pressure, and edema, reducing subsequent secondary injury. The following review examines recent preclinical and clinical studies on HBOT in the context of TBI with a focus on contributing mechanisms and clinical potential. Several preclinical studies have identified pathways, such as TLR4/NF-kB, that are affected by HBOT and contribute to its therapeutic effect. Thus far, the mechanisms mediating HBOT treatment have yet to be fully elucidated and are of interest to researchers. Nonetheless, multiple clinical studies presented in this review have examined the safety of HBOT and demonstrated the improved neurological function of TBI patients after HBOT, deeming it a promising avenue for treatment.

The application and perspective of hyperbaric oxygen therapy in acute ischemic stroke: From the bench to a starter?

Stroke has become a significant cause of death and disability globally. Along with the transition of the world's aging population, the incidence of acute ischemic stroke is increasing year by year. Even with effective treatment modalities, patients are not guaranteed to have a good prognosis. The treatment model combining intravenous thrombolysis/endovascular therapy and neuroprotection is gradually being recognized. After the clinical translation of pharmacological neuroprotective agents failed, non-pharmacological physical neuroprotective agents have rekindled hope. We performed a literature review using the National Center for Biotechnology Information (NCBI) PubMed database for studies that focused on the application of hyperbaric oxygen therapy in acute ischemic stroke. In this review, we present the history and mechanisms of hyperbaric oxygen therapy, focusing on the current status, outcomes, current challenges, perspective, safety, and complications of the application of hyperbaric oxygen in animal experiments and human clinical trials. Hyperbaric oxygen therapy, a non-pharmacological treatment, can improve the oxygenation level at the ischemic lesions in increased dissolved oxygen and oxygen diffusion radius to achieve salvage of neurological function, giving a new meaning to acute ischemic stroke.

Systematic Review and Dosage Analysis: Hyperbaric Oxygen Therapy Efficacy in Mild Traumatic Brain Injury Persistent Postconcussion Syndrome

Background

Mild traumatic brain injury results in over 15% of patients progressing to Persistent Postconcussion Syndrome, a condition with significant consequences and limited treatment options. Hyperbaric oxygen therapy has been applied to Persistent Postconcussion Syndrome with conflicting results based on its historical understanding/definition as a disease-specific therapy. This is a systematic review of the evidence for hyperbaric oxygen therapy (HBOT) in Persistent Postconcussion Syndrome using a dose-analysis that is based on the scientific definition of hyperbaric oxygen therapy as a dual-component drug composed of increased barometric pressure and hyperoxia.

Methods

In this review, PubMed, CINAHL, and the Cochrane Systematic Review Database were searched from August 8–22, 2021 for all adult clinical studies published in English on hyperbaric oxygen therapy in mild traumatic brain injury Persistent Postconcussion Syndrome (symptoms present at least 3 months). Randomized trials and studies with symptomatic and/or cognitive outcomes were selected for final analysis. Randomized trials included those with no-treatment control groups or control groups defined by either the historical or scientific definition. Studies were analyzed according to the dose of oxygen and barometric pressure and classified as Levels 1–5 based on significant immediate post-treatment symptoms or cognitive outcomes compared to control groups. Levels of evidence classifications were made according to the Centre for Evidence-Based Medicine and a practice recommendation according to the American Society of Plastic Surgeons. Methodologic quality and bias were assessed according to the PEDro Scale.

Results

Eleven studies were included: six randomized trials, one case-controlled study, one case series, and three case reports. Whether analyzed by oxygen, pressure, or composite oxygen and pressure dose of hyperbaric therapy statistically significant symptomatic and cognitive improvements or cognitive improvements alone were achieved for patients treated with 40 HBOTS at 1.5 atmospheres absolute (ATA) (four randomized trials). Symptoms were also improved with 30 treatments at 1.3 ATA air (one study), positive and negative results were obtained at 1.2 ATA air (one positive and one negative study), and negative results in one study at 2.4 ATA oxygen. All studies involved <75 subjects/study. Minimal bias was present in four randomized trials and greater bias in 2.

Conclusion

In multiple randomized and randomized controlled studies HBOT at 1.5 ATA oxygen demonstrated statistically significant symptomatic and cognitive or cognitive improvements alone in patients with mild traumatic brain injury Persistent Postconcussion Syndrome. Positive and negative results occurred at lower and higher doses of oxygen and pressure. Increased pressure within a narrow range appears to be the more important effect than increased oxygen which is effective over a broad range. Improvements were greater when patients had comorbid Post Traumatic Stress Disorder. Despite small sample sizes, the 1.5 ATA HBOT studies meet the Centre for Evidence-Based Medicine Level 1 criteria and an American Society of Plastic Surgeons Class A Recommendation for HBOT treatment of mild traumatic brain injury persistent postconcussion syndrome.

Hyperbaric oxygen therapy after mid-cervical spinal contusion injury

Hyperbaric oxygen (HBO) therapy is frequently used to treat peripheral wounds or decompression sickness. Evidence suggests that HBO therapy can provide neuroprotection and has an anti-inflammatory impact after neurological injury, including spinal cord injury (SCI). Our primary purpose was to conduct a genome-wide screening of mRNA expression changes in the injured spinal cord after HBO therapy. An mRNA gene array was used to evaluate samples taken from the contused region of the spinal cord following a lateralized mid-cervical contusion injury in adult female rats. HBO therapy consisted of daily, 1-h sessions (3.0 ATA, 100% O₂) initiated on the day of SCI and continued for 10 days. Gene set enrichment analyses indicated that HBO upregulated genes in pathways associated with electron transport, mitochondrial function, and oxidative phosphorylation, and downregulated genes in pathways associated with inflammation (including cytokines and nuclear factor kappa B [NF-κB]) and apoptotic signaling. In a separate cohort, spinal cord histology was performed to verify whether the HBO treatment impacted neuronal cell counts or inflammatory markers. Compared with untreated rats, there were increased NeuN positive cells in the spinal cord of HBO-treated rats (p = 0.004). We conclude that HBO therapy, initiated shortly after SCI and continued for 10 days, can alter the molecular signature of the lesioned spinal cord in a manner consistent with a neuroprotective impact.

Effects of Hyperoxia on Aging Biomarkers: A Systematic Review

The effects of short-term hyperoxia on age-related diseases and aging biomarkers have been reported in animal and human experiments using different protocols; however, the findings of the studies remain conflicting. In this systematic review, we summarized the existing reports in the effects of short-term hyperoxia on age-related diseases, hypoxia-inducible factor 1α (HIF-1α), and other oxygen-sensitive transcription factors relevant to aging, telomere length, cellular senescence, and its side effects. This review was done as described in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. A systematic search was done in PubMed, Google Scholar, and Cochrane Library and from the references of selected articles to identify relevant studies until May 2021. Of the total 1,699 identified studies, 17 were included in this review. Most of the studies have shown significant effects of short-term hyperoxia on age-related diseases and aging biomarkers. The findings of the studies suggest the potential benefits of short-term hyperoxia in several clinical applications such as for patients undergoing stressful operations, restoration of cognitive function, and the treatment of severe traumatic brain injury. Short-term hyperoxia has significant effects in upregulation or downregulation of transcription factors relevant to aging such as HIF-1α, nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-kB), and nuclear factor (erythroid-derived 2)-like 2 (NRF2) among others. Short-term hyperoxia also has significant effects to increase antioxidant enzymes, and increase telomere length and clearance of senescent cells. Some of the studies have also reported adverse consequences including mitochondrial DNA damage and nuclear cataract formation depending on the dose and duration of oxygen exposure. In conclusion, short-term hyperoxia could be a feasible treatment option to treat age-related disease and to slow aging because of its ability to increase antioxidant enzymes, significantly increase telomere length and clearance of senescent cells, and improve cognitive function, among others. The reported side effects of hyperoxia vary depending on the dose and duration of exposure. Therefore, it seems that additional studies for better understanding the beneficial effects of short-term hyperoxia and for minimizing side effects are necessary for optimal clinical application.

Comparison of Different Physical Therapies Combined with Acupuncture for Poststroke Cognitive Impairment: a Network Meta-Analysis

Objective

Physical therapy combined with acupuncture is the current research hotspot in the treatment of poststroke cognitive impairment, but which combination treatment is the best is still controversial. Based on the network meta-analysis method, we evaluated the efficacy of various physical therapies combined with acupuncture for the treatment of poststroke cognitive impairment.

Methods

We retrieved diverse randomized controlled trials of various physical therapies combined with acupuncture for the treatment of cognitive dysfunction after stroke. We selected studies, extracted data, and evaluated the risk of literature bias for the included randomized controlled trials. We used STATA 14.0 for the current network meta-analysis.

Results

Fifteen randomized controlled trials involving 1288 patients were included, which involved 7 treatment plans that included 3 control treatment plans and 4 acupuncture treatment plans combined with physical therapy. The best treatment plan for improving the Mini-Mental State Examination score of poststroke cognitive impairment is acupuncture combined with hyperbaric oxygen therapy. The best treatment option for improving the Montreal Cognitive Assessment score of poststroke cognitive impairment is acupuncture combined with hyperbaric oxygen therapy. The best option for improving the Barthel index score of poststroke cognitive impairment is acupuncture combined with transcranial magnetic stimulation. In terms of improving the overall clinical effectiveness of poststroke cognitive impairment, the best treatment option is acupuncture combined with transcranial magnetic stimulation.

Conclusion

The analysis of all the results shows that acupuncture combined with hyperbaric oxygen therapy can significantly improve poststroke cognitive impairment compared with other combined treatments. However, due to the overall quality and quantity of the included studies, more randomized controlled trials focusing on clinical research on acupuncture combined with physical therapy for poststroke cognitive impairment are required to support the current evidence. This trial is registered with CRD42020200092.

Inhalational Gases for Neuroprotection in Traumatic Brain Injury

Despite multiple prior pharmacological trials in traumatic brain injury (TBI), the search for an effective, safe, and practical treatment of these patients remains ongoing. Given the ease of delivery and rapid absorption into the systemic circulation, inhalational gases that have neuroprotective properties will be an invaluable resource in the clinical management of TBI patients. In this review, we perform a systematic review of both pre-clinical and clinical reports describing inhalational gas therapy in the setting of TBI. Hyperbaric oxygen, which has been investigated for many years, and some of the newest developments are reviewed. Also, promising new therapies such as hydrogen gas, hydrogen sulfide gas, and nitric oxide are discussed. Moreover, novel therapies such as xenon and argon gases and delivery methods using microbubbles are explored.

A review on the neuroprotective effects of hyperbaric oxygen therapy

Hyperbaric oxygen therapy, intermittent breathing of 100% oxygen at a pressure upper than sea level, has been shown to be some of the neuroprotective effects and used therapeutically in a wide range of neurological disorders. This review summarizes current knowledge about the neuroprotective effects of hyperbaric oxygen therapy with their molecular mechanisms in different models of neurological disorders.

Molecular and Therapeutic Aspects of Hyperbaric Oxygen Therapy in Neurological Conditions

In hyperbaric oxygen therapy (HBOT), the subject is placed in a chamber containing 100% oxygen gas at a pressure of more than one atmosphere absolute. This treatment is used to hasten tissue recovery and improve its physiological aspects, by providing an increased supply of oxygen to the damaged tissue. In this review, we discuss the consequences of hypoxia, as well as the molecular and physiological processes that occur in subjects exposed to HBOT. We discuss the efficacy of HBOT in treating neurological conditions and neurodevelopmental disorders in both humans and animal models. We summarize by discussing the challenges in this field, and explore future directions that will allow the scientific community to better understand the molecular aspects and applications of HBOT for a wide variety of neurological conditions.

The Effect of Hyperbaric Oxygen Therapy on Functional Impairments Caused by Ischemic Stroke

Background

While research suggests a benefit of hyperbaric oxygen therapy (HBOT) for neurologic injury, controlled clinical trials have not been able to clearly define the benefits.

Objective

To investigate the effects of HBOT on physical and cognitive impairments resulting from an ischemic stroke.

Methods

Using a within-subject design a baseline for current functional abilities was established over a 3-month period for all subjects (n=7). Each subject then received two 4-week periods of HBOT for a total of 40 90-minute treatments over a 12-week period. Subjects completed a battery of assessments and had blood drawn six times over the 9-month total duration of the study.

Results

We found improvements in cognition and executive function as well as physical abilities, specifically, improved gait. Participants reported improved sleep and quality of life following HBOT treatment. We also saw changes in serum levels of biomarkers for inflammation and neural recovery. In the functional domains where improvement was observed following HBOT treatment, the improvements were maintained up to 3 months following the last treatment. However, the physiological biomarkers showed a pattern of more transient changes following HBOT treatment.

Conclusions

Findings from this study support the idea of HBOT as a potential intervention following stroke.

Is Hyperbaric Oxygen Therapy Effective for Traumatic Brain Injury? A Rapid Evidence Assessment of the Literature and Recommendations for the Field

Supplemental Digital Content is Available in the Text.

Objective:

This systematic review examines the efficacy of hyperbaric oxygen (HBO₂) for traumatic brain injury (TBI) to make evidence-based recommendations for its application and future research.

Methods:

A comprehensive search was conducted to identify studies through 2014. Methodological quality was assessed and synthesis and interpretation of relevant data was performed.

Results:

Twelve randomized trials were included. All mild TBI studies demonstrated minimal bias and no statistically significant differences between HBO₂ and sham arms. Statistically significant improvement occurred over time within both groups. Moderate-to-severe TBI studies were of mixed quality, with majority of results favoring HBO₂ compared with “standard care.” The placebo analysis conducted was limited by lack of details.

Conclusions:

For mild TBI, results indicate HBO₂ is no better than sham treatment. Improvements within both HBO₂ and sham groups cannot be ignored. For acute treatment of moderate-to-severe TBI, although methodology appears flawed across some studies, because of the complexity of brain injury, HBO₂ may be beneficial as a relatively safe adjunctive therapy if feasible. Further research should be considered to resolve the controversy surrounding this field, but only if methodological flaws are avoided and bias minimized.

Hyperbaric Oxygen Therapy in the Treatment of Acute Severe Traumatic Brain Injury: A Systematic Review

There has been no major advancement in a quarter of a century for the treatment of acute severe traumatic brain injury (TBI). This review summarizes 40 years of clinical and pre-clinical research on the treatment of acute TBI with hyperbaric oxygen therapy (HBO₂) in the context of an impending National Institute of Neurologic Disorders and Stroke-funded, multi-center, randomized, adaptive Phase II clinical trial -the Hyperbaric Oxygen Brain Injury Treatment (HOBIT) trial. Thirty studies (eight clinical and 22 pre-clinical) that administered HBO₂ within 30 days of a TBI were identified from PubMed searches. The pre-clinical studies consistently reported positive treatment effects across a variety of outcome measures with almost no safety concerns, thus providing strong proof-of-concept evidence for treating severe TBI in the acute setting. Of the eight clinical studies reviewed, four were based on the senior author's (GR) investigation of HBO₂ as a treatment for acute severe TBI. These studies provided evidence that HBO₂ significantly improves physiologic measures without causing cerebral or pulmonary toxicity and can potentially improve clinical outcome. These results were consistent across the other four reviewed clinical studies, thus providing preliminary clinical data supporting the HOBIT trial. This comprehensive review demonstrates that HBO₂ has the potential to be the first significant treatment in the acute phase of severe TBI.

Hyperbaric oxygen therapy for traumatic brain injury: bench-to-bedside

Traumatic brain injury (TBI) is a serious public health problem in the United States. Survivors of TBI are often left with significant cognitive, behavioral, and communicative disabilities. So far there is no effective treatment/intervention in the daily clinical practice for TBI patients. The protective effects of hyperbaric oxygen therapy (HBOT) have been proved in stroke; however, its efficiency in TBI remains controversial. In this review, we will summarize the results of HBOT in experimental and clinical TBI, elaborate the mechanisms, and bring out our current understanding and opinions for future studies.

Treatment of persistent post-concussion syndrome due to mild traumatic brain injury: current status and future directions

Persistent post-concussion syndrome caused by mild traumatic brain injury has become a major cause of morbidity and poor quality of life. Unlike the acute care of concussion, there is no consensus for treatment of chronic symptoms. Moreover, most of the pharmacologic and non-pharmacologic treatments have failed to demonstrate significant efficacy on both the clinical symptoms as well as the pathophysiologic cascade responsible for the permanent brain injury. This article reviews the pathophysiology of PCS, the diagnostic tools and criteria, the current available treatments including pharmacotherapy and different cognitive rehabilitation programs, and promising new treatment directions. A most promising new direction is the use of hyperbaric oxygen therapy, which targets the basic pathological processes responsible for post-concussion symptoms; it is discussed here in depth.

Effects of adenosine metabolism in astrocytes on central nervous system oxygen toxicity

Hyperbaric oxygen (HBO) is widely used in military operations, especially underwater missions. However, prolonged and continuous inhalation of HBO can cause central nervous system oxygen toxicity (CNS-OT), which greatly limits HBO's application. The regulation of astrocytes to the metabolism of adenosine is involved in epilepsy. In our study, we aimed to observe the effects of HBO exposure on the metabolism of adenosine in the brain. Furthermore, we aimed to confirm the possible mechanism underlying adenosine's mediation of the CNS-OT. Firstly, anesthetized rats exposed to 5 atm absolute HBO for 80 min. The concentrations of extracellular adenosine, ATP, ADP, and AMP were detected. Secondly, free-moving rats were exposed to HBO at the same pressure for 20 min, and the activities of 5'-nucleotidase and ADK in brain tissues were measured. For the mechanism studies, we observed the effects of a series of different doses of drugs related to adenosine metabolism on the latency of CNS-OT. Results showed HBO exposure could increase adenosine content by inhibiting ADK activity and improving 5'-nucleotidase activity. And adenosine metabolism during HBO exposure may be a protective response against HBO-induced CNS-OT. Moreover, the improvement of adenosine concentration, activation of adenosine A1R, or suppression of ADK and adenosine A2AR, which are involved in the prevention of HBO-induced CNS-OT. This is the first study to demonstrate HBO exposure regulated adenosine metabolism in the brain. Adenosine metabolism and adenosine receptors are related to HBO-induced CNS-OT development. These results will provide new potential targets for the termination or the attenuation of CNS-OT.

Hyperbaric oxygen therapy for the treatment of traumatic brain injury: a meta-analysis

Compelling evidence suggests the advantage of hyperbaric oxygen therapy (HBOT) in traumatic brain injury. The present meta-analysis evaluated the outcomes of HBOT in patients with traumatic brain injury (TBI). Prospective studies comparing hyperbaric oxygen therapy vs. control in patients with mild (GCS 13-15) to severe (GCS 3-8) TBI were hand-searched from medical databases using the terms "hyperbaric oxygen therapy, traumatic brain injury, and post-concussion syndrome". Glasgow coma scale (GCS) was the primary outcome, while Glasgow outcome score (GOS), overall mortality, and changes in post-traumatic stress disorder (PTSD) score, constituted the secondary outcomes. The results of eight studies (average age of patients, 23-41 years) reveal a higher post-treatment GCS score in the HBOT group (pooled difference in means = 3.13, 95 % CI 2.34-3.92, P < 0.001), in addition to greater improvement in GOS and lower mortality, as compared to the control group. However, no significant change in the PTSD score was observed. Patients undergoing hyperbaric therapy achieved significant improvement in the GCS and GOS with a lower overall mortality, suggesting its utility as a standard intensive care regimen in traumatic brain injury.

Neuroprotection in acute brain injury: an up-to-date review

Neuroprotective strategies that limit secondary tissue loss and/or improve functional outcomes have been identified in multiple animal models of ischemic, hemorrhagic, traumatic and nontraumatic cerebral lesions. However, use of these potential interventions in human randomized controlled studies has generally given disappointing results. In this paper, we summarize the current status in terms of neuroprotective strategies, both in the immediate and later stages of acute brain injury in adults. We also review potential new strategies and highlight areas for future research.

Treatment Progress of Paroxysmal Sympathetic Hyperactivity after Acquired Brain Injury

Paroxysmal sympathetic hyperactivity (PSH) is a common complication of various acquired brain injuries such as traumatic brain injury, subarachnoid hemorrhage, anoxic brain injury, intracerebral hemorrhage, and others. It is manifested by tachycardia, hypertension, tachypnea, diaphoresis, and dystonic posturing. The development of PSH can prolong hospitalization and lead to secondary brain injury and even death. Despite the awareness of the serious clinical impact, there is no consensus on diagnostic criteria. Thus, misdiagnosis and delayed recognition is very common. Most of the current treatment programs come from case reports and small case series; there are very few large-scale randomized controlled trials. Generally accepted medications are opioids, β-blockers and gabapentin (usually used in combination). However, the efficacy of these drugs has not been systematically assessed. The purpose of this review is to determine the treatment strategies and drugs commonly used for PSH at the overall level.

Clinical management of the minimally conscious state

The minimally conscious state (MCS) was defined as a disorder of consciousness (DoC) distinct from the vegetative state more than a decade ago. While this condition has become widely recognized, there are still no guidelines to steer the approach to assessment and treatment. The development of evidence-based practice guidelines for MCS has been hampered by ambiguity around the concept of consciousness, the lack of accurate methods of assessment, and the dearth of well-designed clinical trials. This chapter provides a critical review of existing assessment procedures, critically reviews available treatment options and identifies knowledge gaps. We close with practice-based recommendations for a rational approach to clinical management of this challenging population.

Hyperbaric oxygen treatment in the experimental spinal cord injury model

BACKGROUND CONTEXT

Spinal cord trauma is a major cause of mortality and morbidity. Although no known treatment for spinal cord injury exists, a limited number of effective treatment modalities and procedures are available that improve secondary injury. Hyperbaric oxygen (HBO) treatment has been used to assist in neurologic recovery after cranial injury or ischemic stroke.

PURPOSE

To report the findings on the effectiveness of HBO treatment on rats with experimental traumatic spinal cord injury. Improvement was evaluated through motor strength assessment and nitrite level assay testing.

STUDY DESIGN

We randomly distributed 40 rats among 5 groups of 8 rats each: sham incurable trauma, induced trauma, HBO treatment begun at the 1st hour, HBO treatment begun at the 6th hour, and HBO treatment begun at the 24th hour.

METHOD

The HBO treatment was administered to rats in three of the groups and conducted in two 90-minute sessions, under an absolute atmospheric pressure of 2.4 at 100% oxygen for 5 days. In the motor strength evaluations, all the rats were observed during the inclined plane test and clinical motor examination on the first, third, and fifth days. In addition, the nitrite levels of spinal cord tissues on the sixth day were also studied.

RESULTS

Results from the inclined plane levels and motor strength test from all the three groups undergoing HBO treatment were higher than those from Group 2. It was also determined that early HBO treatment resulted in higher recovery rates (groups 3 and 4). The highest levels were seen in the group in which the HBO treatments were started in the first hour (Group 3). It was noted that nitrite levels of rats in the group exposed to trauma increased, compared with the sham group, but increased levels also diminished after HBO treatments. Again, the greatest decrease in nitrite levels was evident in the group where the HBO treatment was started the earliest (Group 3).

CONCLUSIONS

Prompt HBO treatment after trauma significantly contributed to the clinical, histopathologic, and biochemical recovery of the rats.

[Hyperbaric oxygen therapy and inert gases in cerebral ischemia and traumatic brain injury]

Cerebral ischemia is a common thread of acute cerebral lesions, whether vascular or traumatic origin. Hyperbaric oxygen (HBO) improves tissue oxygenation and may prevent impairment of reversible lesions. In experimental models of cerebral ischemia or traumatic brain injury, HBO has neuroprotective effects which are related to various mechanisms such as modulation of oxidative stress, neuro-inflammation or cerebral and mitochondrial metabolism. However, results of clinical trials failed to prove any neuroprotective effects for cerebral ischemia and remained to be confirmed for traumatic brain injury despite preliminary encouraging results. The addition of inert gases to HBO sessions, especially argon or xenon which show neuroprotective experimental effects, may provide an additional improvement of cerebral lesions. Further multicentric studies with a strict methodology and a better targeted definition are required before drawing definitive conclusions about the efficiency of combined therapy with HBO and inert gases in acute cerebral lesions.

Haemoglobin management in acute brain injury

PURPOSE OF REVIEW

Anaemia is common among patients in the neurocritical care unit (NCCU) and is thought to exacerbate brain injury. However, the optimal haemoglobin (Hgb) level still remains to be elucidated for traumatic brain injury (TBI), subarachnoid haemorrhage (SAH) and acute ischaemic stroke (AIS). This review outlines recent studies about anaemia and the effects of red blood cell transfusion (RBCT) on outcome in TBI, SAH and AIS patients admitted to the NCCU.

RECENT FINDINGS

Patients with severe SAH, AIS and TBI often develop anaemia and require RBCT. In general critical care, a restrictive RBCT strategy (Hgb ~7 g/dl) is preferable in patients without serious cardiac disease. In severe TBI, AIS and SAH, both anaemia and RBCT may negatively influence clinical outcome. However, the appropriate RBCT trigger remains unclear and there is great variance in how these patients are transfused. There is evidence from PET and microdialysis studies in humans that RBCT can favourably influence brain metabolism and oxygenation. This correction of hypoxia or altered metabolism rather than anaemia may be of greater importance.

SUMMARY

Results from general critical care should not be extrapolated to all patients with acute brain injury. Transfusion is not risk free, but RBCT use needs to be considered also in terms of potential benefit.

Quantitative evaluation of hyperbaric oxygen efficacy in experimental traumatic brain injury: an MRI study

To use DCE-magnetic resonance imaging (MRI) and diffusion-weighted imaging to evaluate the hyperbaric oxygen efficacy (HBO) in experimental traumatic brain injury (TBI). Forty-two rabbits were randomly divided into four groups: TBI, TBI + HBO, sham group, sham + HBO. The TBI + HBO and sham + HBO received a total of 10 HBO treatments within 7 days following TBI, and MRI was performed within a month after TBI. Functional assessments were performed pre-TBI, and at 1 and 30 days. In focal lesion area, K(trans) in TBI + HBO group was lower than TBI group at both acute and subacute phase (p < 0.05). ADC was higher in TBI + HBO group than TBI group at acute phase (p < 0.01), but lower at subacute phase (p < 0.05). In perifocal area, K(trans) were lower in TBI + HBO group than TBI group at acute phase (p < 0.01) after TBI. ADC was lower in the TBI + HBO group than in the TBI group at both acute and subacute phase (p < 0.01).The VCS was higher in TBI + HBO group than TBI group at 30 days (p < 0.05). HBO could improve the impaired BBB and cytotoxic edema after TBI and promote the recovery of neurofunction.

Hyperbaric oxygenation alters temporal expression pattern of superoxide dismutase 2 after cortical stab injury in rats

Aim

To evaluate the effect of hyperbaric oxygen therapy (HBOT) on superoxide dismutase 2 (SOD2) expression pattern after the cortical stab injury (CSI).

Methods

CSI was performed on 88 male Wistar rats, divided into control, sham, lesioned, and HBO groups. HBOT protocol was the following: pressure applied was 2.5 absolute atmospheres, for 60 minutes, once a day for consecutive 3 or 10 days.‎ The pattern of SOD2 expression and cellular localization was analyzed using real-time polymerase chain reaction, Western blot, and double-label fluorescence immunohistochemistry. Neurons undergoing degeneration were visualized with Fluoro-Jade^®B.

Results

CSI induced significant transient increase in SOD2 protein levels at day 3 post injury, which was followed by a reduction toward control levels at post-injury day 10. At the same time points, mRNA levels for SOD2 in the injured cortex were down-regulated. Exposure to HBO for 3 days considerably down-regulated SOD2 protein levels in the injured cortex, while after 10 days of HBOT an up-regulation of SOD2 was observed. HBOT significantly increased mRNA levels for SOD2 at both time points compared to the corresponding L group, but they were still lower than in controls. Double immunofluorescence staining revealed that 3 days after CSI, up-regulation of SOD2 was mostly due to an increased expression in reactive astrocytes surrounding the lesion site. HBOT attenuated SOD2 expression both in neuronal and astroglial cells. Fluoro-Jade^®B labeling showed that HBOT significantly decreased the number of degenerating neurons in the injured cortex.

Conclusion

HBOT alters SOD2 protein and mRNA levels after brain injury in a time-dependent manner.

Effect of normabaric hyperoxia treatment on neuronal damage following fluid percussion injury in the striatum of mice: a morphological approach

Traumatic brain injury (TBI) causes significant mortality in most developing countries worldwide. At present, it is imperative to identify a treatment to address the devastating post-TBI consequences. Therefore, the present study has been performed to assess the specific effect of immediate exposure to normabaric hyperoxia (NBO) after fluid percussion injury (FPI) in the striatum of mice. To execute FPI, mice were anesthetised and sorted into (i) a TBI group, (ii) a sham group without injury and (iii) a TBI group treated with immediate exposure to NBO for 3 h. Afterwards, brains were harvested for morphological assessment. The results revealed no changes in morphological and neuronal damage in the sham group as compared to the TBI group. Conversely, the TBI group showed severe morphological changes as well as neuronal damage as compared to the TBI group exposed to NBO for 3 h. Interestingly, our findings also suggested that NBO treatment could diminish the neuronal damage in the striatum of mice after FPI. Neuronal damage was evaluated at different points of injury and the neighbouring areas using morphology, neuronal apoptotic cell death and pan-neuronal markers to determine the complete neuronal structure. In conclusion, immediate exposure to NBO following FPI could be a potential therapeutic approach to reduce neuronal damage in the TBI model.

A review of oxygen therapy in ischemic stroke

Neuroprotective drugs have so far failed clinical trials, at high cost, and intravenous tissue plasminogen activator (i.v. tPA) remains the only FDA-approved acute stroke therapy. Hyperoxia, acting via multiple direct and indirect mechanisms, may be a powerful neuroprotective strategy to salvage acutely ischemic brain tissue and extend the time window for acute stroke treatment. Of the available oxygen delivery methods, hyperbaric oxygen therapy (HBO) appears to be the most potent, while even normobaric oxygen therapy (NBO) may be effective if started promptly after stroke onset. HBO has so far failed to show efficacy in three clinical trials. The failure of these trials is probably attributable to factors such as delayed time to therapy, inadequate sample size and use of excessive chamber pressures. Previous trials did not assess long-term benefit in patients with tissue reperfusion. In this modern era of stroke thrombolysis and advanced neuroimaging, oxygen therapy may have renewed significance. If applied within the first few hours after stroke onset or in patients with imaging evidence of salvageable brain tissue, oxygen therapy could be used to 'buy time' for the administration of thrombolytic or neuroprotective drugs. This article reviews the history and current rationale for using oxygen therapy in stroke, the mechanisms of action of HBO and the results of animal and human studies of hyperoxia in cerebrovascular diseases.

A prospective, randomized Phase II clinical trial to evaluate the effect of combined hyperbaric and normobaric hyperoxia on cerebral metabolism, intracranial pressure, oxygen toxicity, and clinical outcome in severe traumatic brain injury

OBJECT

Preclinical and clinical investigations indicate that the positive effect of hyperbaric oxygen (HBO2) for severe traumatic brain injury (TBI) occurs after rather than during treatment. The brain appears better able to use baseline O2 levels following HBO2 treatments. In this study, the authors evaluate the combination of HBO2 and normobaric hyperoxia (NBH) as a single treatment.

METHODS

Forty-two patients who sustained severe TBI (mean Glasgow Coma Scale [GCS] score 5.7) were prospectively randomized within 24 hours of injury to either: 1) combined HBO2/NBH (60 minutes of HBO2 at 1.5 atmospheres absolute [ATA] followed by NBH, 3 hours of 100% fraction of inspired oxygen [FiO2] at 1.0 ATA) or 2) control, standard care. Treatments occurred once every 24 hours for 3 consecutive days. Intracranial pressure, surrogate markers for cerebral metabolism, and O2 toxicity were monitored. Clinical outcome was assessed at 6 months using the sliding dichotomized Glasgow Outcome Scale (GOS) score. Mixed-effects linear modeling was used to statistically test differences between the treatment and control groups. Functional outcome and mortality rates were compared using chi-square tests.

RESULTS

There were no significant differences in demographic characteristics between the 2 groups. In comparison with values in the control group, brain tissue partial pressure of O2 (PO2) levels were significantly increased during and following combined HBO2/NBH treatments in both the noninjured and pericontusional brain (p < 0.0001). Microdialysate lactate/pyruvate ratios were significantly decreased in the noninjured brain in the combined HBO2/NBH group as compared with controls (p < 0.0078). The combined HBO2/NBH group's intracranial pressure values were significantly lower than those of the control group during treatment, and the improvement continued until the next treatment session (p < 0.0006). The combined HBO2/NBH group's levels of microdialysate glycerol were significantly lower than those of the control group in both noninjured and pericontusional brain (p < 0.001). The combined HBO2/NBH group's level of CSF F2-isoprostane was decreased at 6 hours after treatment as compared with that of controls, but the difference did not quite reach statistical significance (p = 0.0692). There was an absolute 26% reduction in mortality for the combined HBO2/NBH group (p = 0.048) and an absolute 36% improvement in favorable outcome using the sliding dichotomized GOS (p = 0.024) as compared with the control group.

CONCLUSIONS

In this Phase II clinical trial, in comparison with standard care (control treatment) combined HBO2/NBH treatments significantly improved markers of oxidative metabolism in relatively uninjured brain as well as pericontusional tissue, reduced intracranial hypertension, and demonstrated improvement in markers of cerebral toxicity. There was significant reduction in mortality and improved favorable outcome as measured by GOS. The combination of HBO2 and NBH therapy appears to have potential therapeutic efficacy as compared with the 2 treatments in isolation. CLINICAL TRIAL REGISTRATION NO.: NCT00170352 (ClinicalTrials.gov).

Mitochondria in traumatic brain injury and mitochondrial-targeted multipotential therapeutic strategies

Traumatic brain injury (TBI) is a major health and socioeconomic problem throughout the world. It is a complicated pathological process that consists of primary insults and a secondary insult characterized by a set of biochemical cascades. The imbalance between a higher energy demand for repair of cell damage and decreased energy production led by mitochondrial dysfunction aggravates cell damage. At the cellular level, the main cause of the secondary deleterious cascades is cell damage that is centred in the mitochondria. Excitotoxicity, Ca(2+) overload, reactive oxygen species (ROS), Bcl-2 family, caspases and apoptosis inducing factor (AIF) are the main participants in mitochondria-centred cell damage following TBI. Some preclinical and clinical results of mitochondria-targeted therapy show promise. Mitochondria- targeted multipotential therapeutic strategies offer new hope for the successful treatment of TBI and other acute brain injuries.

Physiopathology of anemia and transfusion thresholds in isolated head injury

BACKGROUND

Blood transfusion strategies among patients with critical illness use a restrictive hemoglobin threshold. However, among patients with head injury, no outcome differences have been shown between either liberal or restrictive strategies. Several studies and literature reviews suggest that anemia is associated with markers of tissue ischemia. The paucity of prospective data confuses the association between surrogates of tissue ischemia and neurological outcome.

METHODS

A narrative review of transfusion practices among patients in the acute phase of head injury was performed using PubMed, MEDLINE, EMBASE, Cochrane, and WEB of Science databases. A total of 104 articles were reviewed.

RESULTS

There are few data to guide clinical practice. Clinicians use blood hemoglobin concentrations to trigger transfusion. Markers of potential cerebral injury are not in regular use despite experimental and observational data rising from histologic examination, microdialysis, oximetry, and flow-based multimonitoring systems recommending their use to titrate blood transfusion in neurotrauma.

CONCLUSION

The generalization of transfusion triggers is common practice. Evidence-based approaches to transfusions strategies in head injury are lacking and not based on an understanding of cerebral physiopathology.

Role of hyperbaric oxygen therapy in severe head injury in children

Aim:

A brain injury results in a temporary or permanent impairment of cognitive, emotional, and/or physical function. Predicting the outcome of pediatric brain injury is difficult. Prognostic instruments are not precise enough to reliably predict individual patient's mortality and long-term functional status. The purpose of this article is to provide a guide to the strengths and limitations of the use of hyperbaric oxygen therapy (HBOT) in treating pediatric patients with severe brain injury.

Materials and Methods:

We studied total 56 patients of head injury. Out of them 28 received HBOT. Only cases with severe head injury [Glasgow Coma Scale (GCS) < 8] with no other associated injury were included in the study group. After an initial period of resuscitation and conservative management (10–12 days), all were subjected to three sessions of HBOT at 1-week interval. This study group was compared with a control group of similar severity of head injury (GCS < 8).

Results:

The study and control groups were compared in terms of duration of hospitalization, GCS, disability reduction,and social behavior. Patients who received HBOT were significantly better than the control group on all the parameters with decreased hospital stay, better GCS, and drastic reduction in disability.

Conclusion:

In children with traumatic brain injury, the addition of HBOT significantly improved outcome and quality of life and reduced the risk of complications.

Hyperbaric oxygen and hyperbaric air treatment result in comparable neuronal death reduction and improved behavioral outcome after transient forebrain ischemia in the gerbil

Anoxic brain injury resulting from cardiac arrest is responsible for approximately two-thirds of deaths. Recent evidence suggests that increased oxygen delivered to the brain after cardiac arrest may be an important factor in preventing neuronal damage, resulting in an interest in hyperbaric oxygen (HBO) therapy. Interestingly, increased oxygen supply may be also reached by application of normobaric oxygen (NBO) or hyperbaric air (HBA). However, previous research also showed that the beneficial effect of hyperbaric treatment may not directly result from increased oxygen supply, leading to the conclusion that the mechanism of hyperbaric prevention of brain damage is not well understood. The aim of our study was to compare the effects of HBO, HBA and NBO treatment on gerbil brain condition after transient forebrain ischemia, serving as a model of cardiac arrest. Thereby, we investigated the effects of repetitive HBO, HBA and NBO treatment on hippocampal CA1 neuronal survival, brain temperature and gerbils behavior (the nest building), depending on the time of initiation of the therapy (1, 3 and 6 h after ischemia). HBO and HBA applied 1, 3 and 6 h after ischemia significantly increased neuronal survival and behavioral performance and abolished the ischemia-evoked brain temperature increase. NBO treatment was most effective when applied 1 h after ischemia; later application had a weak or no protective effect. The results show that HBO and HBA applied between 1 and 6 h after ischemia prevent ischemia-evoked neuronal damage, which may be due to the inhibition of brain temperature increase, as a result of the applied rise in ambient pressure, and just not due to the oxygen per se. This perspective is supported by the finding that NBO treatment was less effective than HBO or HBA therapy. The results presented in this paper may pave the way for future experimental studies dealing with pressure and temperature regulation.

Brain tissue oxygen monitoring and hyperoxic treatment in patients with traumatic brain injury

Cerebral ischemia is a well-recognized contributor to high morbidity and mortality after traumatic brain injury (TBI). Standard of care treatment aims to maintain a sufficient oxygen supply to the brain by avoiding increased intracranial pressure (ICP) and ensuring a sufficient cerebral perfusion pressure (CPP). Devices allowing direct assessment of brain tissue oxygenation have showed promising results in clinical studies, and their use was implemented in the Brain Trauma Foundation Guidelines for the treatment of TBI patients in 2007. Results of several studies suggest that a brain tissue oxygen-directed therapy guided by these monitors may contribute to reduced mortality and improved outcome of TBI patients. Whether increasing the oxygen supply to supraphysiological levels has beneficial or detrimental effects on TBI patients has been a matter of debate for decades. The results of trials of hyperbaric oxygenation (HBO) have failed to show a benefit, but renewed interest in normobaric hyperoxia (NBO) in the treatment of TBI patients has emerged in recent years. With the increased availability of advanced neuromonitoring devices such as brain tissue oxygen monitors, it was shown that some patients might benefit from this therapeutic approach. In this article, we review the pathophysiological rationale and technical modalities of brain tissue oxygen monitors, as well as its use in studies of brain tissue oxygen-directed therapy. Furthermore, we analyze hyperoxia as a treatment option in TBI patients, summarize the results of clinical trials, and give insights into the recent findings of hyperoxic effects on cerebral metabolism after TBI.

Attenuating inflammation but stimulating both angiogenesis and neurogenesis using hyperbaric oxygen in rats with traumatic brain injury

BACKGROUND

Inflammation, angiogenesis, neurogenesis, and gliosis are involved in traumatic brain injury (TBI). Several studies provide evidence supporting the neuroprotective effect of hyperbaric oxygen (HBO2) therapy in TBI. The aim of this study was to ascertain whether inflammation, angiogenesis, neurogenesis, and gliosis during TBI are affected by HBO2 therapy.

METHODS

Rats were randomly divided into three groups: TBI + NBA (normobaric air: 21% O2 at 1 absolute atmospheres), TBI + HBO2, and Sham operation + NBA. TBI + HBO2 rats received 100% O2 at 2.0 absolute atmospheres for 1 hr/d for three consecutive days. Behavioral tests and biochemical and histologic evaluations were done 4 days after TBI onset.

RESULTS

TBI + NBA rats displayed: (1) motor and cognitive dysfunction; (2) cerebral infarction and apoptosis; (3) activated inflammation (evidenced by increased brain myeloperoxidase activity and higher serum levels of tumor necrosis factor-α); (4) neuronal loss (evidenced by fewer NeuN-positive cells); and (5) gliosis (evidenced by more glial fibrillary protein-positive cells). In TBI + HBO2 rats, HBO2 therapy significantly reduced TBI-induced motor and cognitive dysfunction, cerebral infarction and apoptosis, activated inflammation, neuronal loss, and gliosis. In addition, HBO2 therapy stimulated angiogenesis (evidenced by more bromodeoxyuridine-positive endothelial and vascular endothelial growth factor-positive cells), neurogenesis (evidenced by more bromodeoxyuridine-NeuN double-positive and glial cells-derived neurotrophic factor-positive cells), and overproduction of interleukin-10 (an anti-inflammatory cytokine).

CONCLUSIONS

Collectively, these results suggest that HBO2 therapy may improve outcomes of TBI in rats by inhibiting activated inflammation and gliosis while stimulating both angiogenesis and neurogenesis in the early stage.

Preventing flow-metabolism uncoupling acutely reduces axonal injury after traumatic brain injury

We have previously presented evidence that the development of secondary traumatic axonal injury is related to the degree of local cerebral blood flow (LCBF) and flow-metabolism uncoupling. We have now tested the hypothesis that augmenting LCBF in the acute stages after brain injury prevents further axonal injury. Data were acquired from rats with or without acetazolamide (ACZ) that was administered immediately following controlled cortical impact injury to increase cortical LCBF. Local cerebral metabolic rate for glucose (LCMRglc) and LCBF measurements were obtained 3 h post-trauma in the same rat via ¹⁸F-fluorodeoxyglucose and ¹⁴C-iodoantipyrine co-registered autoradiographic images, and compared to the density of damaged axonal profiles in adjacent sections, and in additional groups at 24 h used to assess different populations of injured axons stereologically. ACZ treatment significantly and globally elevated LCBF twofold above untreated-injured rats at 3 h (p<0.05), but did not significantly affect LCMRglc. As a result, ipsilateral LCMRglc:LCBF ratios were reduced by twofold to sham-control levels, and the density of β-APP-stained axons at 24 h was significantly reduced in most brain regions compared to the untreated-injured group (p<0.01). Furthermore, early LCBF augmentation prevented the injury-associated increase in the number of stained axons from 3-24 h. Additional robust stereological analysis of impaired axonal transport and neurofilament compaction in the corpus callosum and cingulum underlying the injury core confirmed the amelioration of β-APP axon density, and showed a trend, but no significant effect, on RMO14-positive axons. These data underline the importance of maintaining flow-metabolism coupling immediately after injury in order to prevent further axonal injury, in at least one population of injured axons.

Hyperbaric oxygen therapy for traumatic brain injury

Traumatic brain injury (TBI) is a major public health issue. The complexity of TBI has precluded the use of effective therapies. Hyperbaric oxygen therapy (HBOT) has been shown to be neuroprotective in multiple neurological disorders, but its efficacy in the management of TBI remains controversial. This review focuses on HBOT applications within the context of experimental and clinical TBI. We also discuss its potential neuroprotective mechanisms. Early or delayed multiple sessions of low atmospheric pressure HBOT can reduce intracranial pressure, improve mortality, as well as promote neurobehavioral recovery. The complimentary, synergistic actions of HBOT include improved tissue oxygenation and cellular metabolism, anti-apoptotic, and anti-inflammatory mechanisms. Thus HBOT may serve as a promising neuroprotective strategy that when combined with other therapeutic targets for TBI patients which could improve long-term outcomes.

Neuroprotective effects of hyperbaric oxygen treatment on traumatic brain injury in the rat

This study was designed to evaluate the potential benefits of hyperbaric oxygen (HBO) in the treatment of traumatic brain injury (TBI). The right cerebral cortex of rats was injured by the impact of a 20-g object dropped from a predetermined height. The rats received HBO treatment at 3 ATA for 60 min after TBI. Neurological behavior score, brain water content, neuronal loss in the hippocampus, and cell apoptosis in brain tissue surrounding the primary injury site were examined to determine brain damage severity. Three and six hours after TBI, HBO-treated rats displayed a significant reduction in brain damage. However, by 12 h after TBI, the efficacy of HBO treatment was considerably attenuated. Furthermore, at 24, 48, and 72 h after TBI, the HBO treatment did not show any notable effects. In contrast, multiple HBO treatments (three or five times in all), even when started 48 h after TBI, remarkably reduced neurology deficit scores and the loss of neuronal numbers in the hippocampus. Although multiple treatments started at 48 h significantly improved neurological behaviors and reduced brain injury, the overall beneficial effects were substantially weaker than those seen after a single treatment at 6 h. These results suggest that: (1) HBO treatment could alleviate brain damage after TBI; (2) a single treatment with HBO has a time limitation of 12 h post-TBI; and (3) multiple HBO treatments have the possibility to extend the post-TBI delivery time window. Therefore, our results clearly suggest the validity of HBO therapy for the treatment of TBI.

Oxygen therapy improves energy metabolism in focal cerebral ischemia

Oxygen therapy (OT) with hyperbaric oxygen (HBO) or normobaric hyperoxia (NBO) improves the oxygenation of penumbral tissue in experimental ischemic stroke. However, whether this results in the improvement of energy metabolism is unclear. We investigated the effect of both OTs on tissue acidosis and on ATP production. Beginning 25 min after filament middle cerebral artery occlusion (MCAO), mice breathed either air, 100% O₂ (NBO), or 100% O₂ at 3 ata (HBO) for 60 min. Regional tissue pH was measured using the umbelliferone fluorescence. Regional ATP concentration was depicted by substrate-specific bioluminescence. Severity of ischemia did not differ among groups in laser-Doppler flowmetry. Both NBO (70.1±14.0 mm³) and, more effectively, HBO (57.2±11.9 mm³) significantly reduced volume of tissue acidosis compared to air (89.4±4.0 mm³), p<0.05). Topographically, acidosis was less pronounced in the medial striatum and in the cortical ischemic border areas. This resulted in significantly smaller volumes of ATP depletion (77.8±7.7 mm³ in air, 61.4±15.2 mm³ in NBO and 51.2±14.4 mm³ in HBO; p<0.05). In conclusion, OT significantly improves energy metabolism in the border zones of focal cerebral ischemia which are the areas protected by OT in this model.

Application of medical gases in the field of neurobiology

Medical gases are pharmaceutical molecules which offer solutions to a wide array of medical needs. This can range from use in burn and stroke victims to hypoxia therapy in children. More specifically however, gases such as oxygen, helium, xenon, and hydrogen have recently come under increased exploration for their potential theraputic use with various brain disease states including hypoxia-ischemia, cerebral hemorrhages, and traumatic brain injuries. As a result, this article will review the various advances in medical gas research and discuss the potential therapeutic applications and mechanisms with regards to the field of neurobiology.

Pretreatment with normobaric and hyperbaric oxygenation worsens cerebral edema and neurologic outcomes in a murine model of surgically induced brain injury

BACKGROUND

Hyperbaric oxygenation is a readily available treatment modality, and its ability to improve neurological outcomes in a variety of animal models has been demonstrated. This study was designed to investigate the use of a single pretreatment regimen of either hyperbaric oxygenation or normobaric oxygenation to determine its effects in a murine model of surgically induced brain injury (SBI).

MATERIALS AND METHODS

Hyperbaric oxygen (2.5ATM, 1 h), normobaric oxygen (100% FIO2, 1 h) or room air (21% FIO2, 1 h) was applied on CD-1 mice immediately, or at 1, 2 or 3 h followed by SBI or sham surgical operation. Neurological assessment of the animals was done by a blinded observer at 24 and 72 h using a 21-point modified Garcia scale, wire hanging test, and beam balance test. The brain edema was evaluated using brain water content at 24 and 72 h after SBI.

RESULTS

There was no statistically significant difference in the mortality rate after treatment compared with the SBI group. The brain water content after SBI was significantly increased in the right (ipsilateral) frontal lobe surrounding the site of surgical resection compared with the sham group. Both hyperbaric and normobaric oxygen treatment significantly increased the brain edema and worsened the neurological outcomes using a 21-point Garcia score compared with the SBI group. The brain edema at 24 h after injury was most pronounced in the group treated with normobaric oxygenation 2 h prior to surgery. These differences disappeared at 72 h after SBI.

CONCLUSION

Immediate pretreatment with either hyperbaric (2.5ATM, 1 h) or normobaric oxygen (100% FIO2, 1 h) increased brain edema and worsened neurological function at 24 h following SBI.

Protection against focal ischemic injury to the brain by trans-sodium crocetinate. Laboratory investigation

OBJECT

Ischemic injury is a potential complication in a variety of surgical procedures and is a particular impediment to the success of surgeries involving highly vulnerable neural tissue. One approach to limiting this form of injury is to enhance metabolic supply to the affected tissue. Trans-sodium crocetinate (TSC) is a carotenoid compound that has been shown to increase tissue oxygenation by facilitating the diffusivity of small molecules, such as oxygen and glucose. The present study examined the ability of TSC to modify oxygenation in ischemic neural tissue and tested the potential neuroprotective effects of TSC in permanent and temporary models of focal cerebral ischemia.

METHODS

Adult male rats (330–370 g) were subjected to either permanent or temporary focal ischemia by simultaneous occlusion of both common carotid arteries and the left middle cerebral artery (3-vessel occlusion [3-VO]). Using the permanent ischemia paradigm, TSC was administered intravenously beginning 10 minutes after the onset of ischemia at 1 of 8 dosages, ranging from 0.023 to 4.580 mg/kg. Cerebral infarct volume was measured 24 hours after the onset of ischemia. The effect of TSC on infarct volume was also tested after temporary (2-hour) ischemia using a dosage of 0.092 mg/kg. In other animals undergoing temporary ischemia, tissue oxygenation was monitored in the ischemic penumbra using a Licox probe.

RESULTS

Administration of TSC reduced infarct volume in a dose-dependent manner in the permanent ischemia model, achieving statistical significance at dosages ranging from 0.046 to 0.229 mg/kg. The most effective dosage of TSC in the permanent ischemia experiment (0.092 mg/kg) was further tested using a temporary (2-hour) ischemia paradigm. Infarct volume was reduced significantly by TSC in this ischemia-reperfusion model as well. Recordings of oxygen levels in the ischemic penumbra of the temporary ischemia model showed that TSC increased tissue oxygenation during vascular occlusion, but reduced the oxygen overshoot (hyperoxygenation) that occurs upon reperfusion.

CONCLUSIONS

The novel carotenoid compound TSC exerts a neuroprotective influence against permanent and temporary ischemic injury when administered soon after the onset of ischemia. The protective mechanism of TSC remains to be confirmed; however, the permissive effect of TSC on the diffusivity of small molecules is a plausible mechanism based on the observed increase in tissue oxygenation in the ischemic penumbra. This represents a form of protection based on “metabolic reflow” that can occur under conditions of partial vascular perfusion. It is particularly noteworthy that TSC could conceivably limit the progression of a wide variety of cellular injury mechanisms by blunting the ischemic challenge to the brain.