Clinical application of hyperbaric oxygenation in the treatment of acute cerebral damage

Reactive Oxygen Species (ROS)-Mediated Antibacterial Oxidative Therapies: Available Methods to Generate ROS and a Novel Option Proposal

The increasing emergence of multidrug-resistant (MDR) pathogens causes difficult-to-treat infections with long-term hospitalizations and a high incidence of death, thus representing a global public health problem. To manage MDR bacteria bugs, new antimicrobial strategies are necessary, and their introduction in practice is a daily challenge for scientists in the field. An extensively studied approach to treating MDR infections consists of inducing high levels of reactive oxygen species (ROS) by several methods. Although further clinical investigations are mandatory on the possible toxic effects of ROS on mammalian cells, clinical evaluations are extremely promising, and their topical use to treat infected wounds and ulcers, also in presence of biofilm, is already clinically approved. Biochar (BC) is a carbonaceous material obtained by pyrolysis of different vegetable and animal biomass feedstocks at 200-1000 °C in the limited presence of O2. Recently, it has been demonstrated that BC's capability of removing organic and inorganic xenobiotics is mainly due to the presence of persistent free radicals (PFRs), which can activate oxygen, H2O2, or persulfate in the presence or absence of transition metals by electron transfer, thus generating ROS, which in turn degrade pollutants by advanced oxidation processes (AOPs). In this context, the antibacterial effects of BC-containing PFRs have been demonstrated by some authors against Escherichia coli and Staphylococcus aureus, thus giving birth to our idea of the possible use of BC-derived PFRs as a novel method capable of inducing ROS generation for antimicrobial oxidative therapy. Here, the general aspects concerning ROS physiological and pathological production and regulation and the mechanism by which they could exert antimicrobial effects have been reviewed. The methods currently adopted to induce ROS production for antimicrobial oxidative therapy have been discussed. Finally, for the first time, BC-related PFRs have been proposed as a new source of ROS for antimicrobial therapy via AOPs.

The Role of Hyperbaric Oxygen Therapy in the Treatment of Surgical Site Infections: A Narrative Review

Surgical site infections (SSIs) are among the most prevalent postoperative complications, with significant morbidity and mortality worldwide. In the past half century, hyperbaric oxygen therapy (HBOT), the administration of 100% oxygen intermittently under a certain pressure, has been used as either a primary or alternative therapy for the management or treatment of chronic wounds and infections. This narrative review aims to gather information and evidence supporting the role of HBOT in the treatment of SSIs. We followed the Scale for the Quality Assessment of Narrative Review Articles (SANRA) guidelines and scrutinized the most relevant studies identified in Medline (via PubMed), Scopus, and Web of Science. Our review indicated that HBOT can result in rapid healing and epithelialization of various wounds and has potential beneficial effects in the treatment of SSIs or other similar infections following cardiac, neuromuscular scoliosis, coronary artery bypass, and urogenital surgeries. Moreover, it was a safe therapeutic procedure in most cases. The mechanisms related to the antimicrobial activity of HBOT include direct bactericidal effects through the formation of reactive oxygen species (ROS), the immunomodulatory effect of HBOT that increase the antimicrobial effects of the immune system, and the synergistic effects of HBOT with antibiotics. We emphasized the essential need for further studies, especially randomized clinical trials and longitudinal studies, to better standardize HBOT procedures as well as to determine its full benefits and possible side effects.

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.

Use of hyperbaric oxygen in traumatic brain injury: retrospective analysis of data of 20 patients treated at a tertiary care centre

Traumatic brain injury (TBI) related impact results in a permanent need for help in performing daily activities. Standard treatment consists of removing the cause, restore perfusion, support metabolic requirement and limit inflammatory and oxidative damage. Hyperbaric oxygen therapy (HBOT) is one such newer promising treatment that enhances neurological recovery to some extent. HBOT is intermittent inhalation of 100% oxygen at greater than normal atmospheric pressure and is internationally accepted for its role in well-defined indications. It is hypothesised that HBO has a role in reviving 'idling neurons', also called the ischemic penumbra defined as area of reduced cerebral blood flow, abolished synaptic activity but preserved structural integrity. We carried out a retrospective analysis of medical records of 20 patients of TBI who had been treated with HBOT in addition to standard management. These were placed in Group A (test group) and received at least 30 sessions of HBO along with standard treatment. The patients were assessed along the Disability Rating Scale (DRS), Glasgow coma scale (GCS) and Rancho Los Amigos Scale (RLAS). Another 20 patients of TBI, matched in age and severity of brain injury, who received standard treatment but not HBOT, were selected as the control group (Group B). Assessment on the DRS showed maximum improvement in patients with scores of 22-24 (vegetative state).The percentage of patients in the test group fell from 45% to 5% whereas only 20% patients in Group B had similar progress. After the treatment, a significantly higher proportion of HBOT treated subjects showed a good response in cognitive functions, as measured by RLA. In group A, 90% patients had a score of ≤ 3 and in Group B 95% had a similar score, which improved to ≥ 3 in 60% patients versus 30% patients respectively. In both groups maximum patients are in 1-6 months post-injury category and within the groups this category showed the greatest recovery, with a greater improvement in the test group as compared to control group.

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.

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

Object

Oxygen delivered in supraphysiological amounts is currently under investigation as a therapy for severe traumatic brain injury (TBI). Hyperoxia can be delivered to the brain under normobaric as well as hyperbaric conditions. In this study the authors directly compare hyperbaric oxygen (HBO2) and normobaric hyperoxia (NBH) treatment effects.

Methods

Sixty-nine patients who had sustained severe TBIs (mean Glasgow Coma Scale Score 5.8) were prospectively randomized to 1 of 3 groups within 24 hours of injury: 1) HBO2, 60 minutes of HBO2 at 1.5 ATA; 2) NBH, 3 hours of 100% fraction of inspired oxygen at 1 ATA; and 3) control, standard care. Treatments occurred once every 24 hours for 3 consecutive days. Brain tissue PO2, microdialysis, and intracranial pressure were continuously monitored. Cerebral blood flow (CBF), arteriovenous differences in oxygen, cerebral metabolic rate of oxygen (CMRO2), CSF lactate and F2-isoprostane concentrations, and bronchial alveolar lavage (BAL) fluid interleukin (IL)–8 and IL-6 assays were obtained pretreatment and 1 and 6 hours posttreatment. Mixed-effects linear modeling was used to statistically test differences among the treatment arms as well as changes from pretreatment to posttreatment.

Results

In comparison with values in the control group, the brain tissue PO2 levels were significantly increased during treatment in both the HBO2 (mean ± SEM, 223 ± 29 mm Hg) and NBH (86 ± 12 mm Hg) groups (p < 0.0001) and following HBO2 until the next treatment session (p = 0.003). Hyperbaric O2 significantly increased CBF and CMRO2 for 6 hours (p ≤ 0.01). Cerebrospinal fluid lactate concentrations decreased posttreatment in both the HBO2 and NBH groups (p < 0.05). The dialysate lactate levels in patients who had received HBO2 decreased for 5 hours posttreatment (p = 0.017). Microdialysis lactate/pyruvate (L/P) ratios were significantly decreased posttreatment in both HBO2 and NBH groups (p < 0.05). Cerebral blood flow, CMRO2, microdialysate lactate, and the L/P ratio had significantly greater improvement when a brain tissue PO2 ≥ 200 mm Hg was achieved during treatment (p < 0.01). Intracranial pressure was significantly lower after HBO2 until the next treatment session (p < 0.001) in comparison with levels in the control group. The treatment effect persisted over all 3 days. No increase was seen in the CSF F2-isoprostane levels, microdialysate glycerol, and BAL inflammatory markers, which were used to monitor potential O2 toxicity.

Conclusions

Hyperbaric O2 has a more robust posttreatment effect than NBH on oxidative cerebral metabolism related to its ability to produce a brain tissue PO2 ≥ 200 mm Hg. However, it appears that O2 treatment for severe TBI is not an all or nothing phenomenon but represents a graduated effect. No signs of pulmonary or cerebral O2 toxicity were present.

Normobaric hyperoxia therapy for traumatic brain injury and stroke: a review

Traumatic brain injury (TBI) and acute ischaemic stroke are major causes of mortality and morbidity and there is an urgent demand for new neuroprotective strategies following the translational failure of neuroprotective drug trials. Oxygen therapy--especially normobaric, may offer a simple and effective therapeutic strategy which we review in this paper. Firstly we review mechanisms underlying the therapeutic effects of hyperoxia (both normobaric and hyperbaric) including mitochondrial rescue, stabilisation of intracranial pressure, attenuation of cortical spreading depression and inducing favourable endothelial-leukocyte interactions, all effects of which are postulated to decrease secondary injury. Next we survey studies using hyperbaric oxygen therapy for TBI and stroke, which formed the basis for early studies on normobaric hyperoxia. Thirdly, we present clinical studies of the efficacy of normobaric hyperoxia on TBI and stroke, emphasising their safety, efficacy and practicality. Finally we consider safety concerns and side effects, particularly pulmonary pathology, respiratory failure and theoretical risks in paediatric patients. A neuroprotective role of normobaric hyperoxia is extremely promising and further studies are warranted.

Hyperbaric oxygen in traumatic brain injury

OBJECTIVES

This critical literature review examines historical and current investigations on the efficacy and mechanisms of hyperbaric oxygen (HBO) treatment in traumatic brain injury (TBI). Potential safety risks and oxygen toxicity, as well as HBO's future potential, are also discussed.

METHODS

Directed literature review.

RESULTS

Historically, cerebral vasoconstriction and increased oxygen availability were seen as the primary mechanisms of HBO in TBI. HBO now appears to be improving cerebral aerobic metabolism at a cellular level, namely, by enhancing damaged mitochondrial recovery. HBO given at the ideal treatment paradigm, 1.5 ATA for 60 minutes, does not appear to produce oxygen toxicity and is relatively safe.

DISCUSSION

The use of HBO in TBI remains controversial. Growing evidence, however, shows that HBO may be a potential treatment for patients with severe brain injury. Further investigations, including a multicenter prospective randomized clinical trial, will be required to definitively define the role of HBO in severe TBI.

Hyperbaric oxygen therapy for traumatic brain injury: a systematic review of the evidence

OBJECTIVE

To identify the benefits and harms of hyperbaric oxygen therapy (HBOT) to treat traumatic brain injury (TBI).

DATA SOURCES

MEDLINE, EMBASE, the Cochrane Library, HealthSTAR, CINAHL, MANTIS, professional society databases, and reference lists. Databases were searched from inception through December 2003.

STUDY SELECTION

We included English-language studies of patients with TBI given HBOT and evaluating functional health outcomes.

DATA EXTRACTION

Data were abstracted by 1 reviewer and checked by a second. Study quality was rated as good, fair, or poor.

DATA SYNTHESIS

Two fair-quality randomized controlled trials of patients with severe brain injury reported conflicting results. One found no difference in mortality (48% HBOT vs 55% control) or morbidity at 1 year. In young patients with brainstem contusion, significantly more regained consciousness at 1 month with HBOT (67%) than control (11%) (P<.03). The other found a significant decrease in mortality in the HBOT group at 1 year (17%) compared with controls (31%) (P=.037). This decrease in mortality was accompanied by an increase in proportion of patients with severe disability. Patients with intracranial pressure (ICP) greater than 20 mmHg or a Glasgow Coma Scale score of 4 to 6 had significantly lower mortality at 1 year than controls. Five observational studies did not provide better evidence of effectiveness or adverse events. Two indicated a potential for initially reducing elevated ICP in some patients. However, rebound elevations higher than pretreatment levels occurred in some patients. Adverse events, including seizures, pulmonary symptoms, and neurologic deterioration, were reported; however, no study systematically assessed adverse events, and none reported adverse events in control groups.

CONCLUSIONS

The evidence for HBOT for TBI is insufficient to prove effectiveness or ineffectiveness, and more high-quality studies are needed. The evidence indicates that there is a small chance of a mortality benefit, which may depend on subgroup selection. The effect on functional status and the incidence and clinical significance of adverse effects are unclear.

Oxygen tension under hyperbaric conditions in healthy pig brain

OBJECTIVE

To investigate the effect of hyperbaric conditions on brain oxygenation, intracranial pressure and brain glucose/lactate levels in healthy non-brain-traumatized animals.

DESIGN AND SETTING

Prospective animal study in a hyperbaric chamber.

SUBJECTS

Twelve adult Landrace/Yorkshire pigs.

INTERVENTIONS

The animals were normoventilated in a pressure-controlled mode according to the open lung concept first at normobaric pressures (FiO2 of 0.4 and 1.0) and subsequently in the hyperbaric chamber at 1.9 and 2.8 bar (both at an FiO2 of 1.0). Under these conditions brain oxygen tension and intracranial pressure were recorded and brain glucose/lactate levels were measured by microdialysis.

RESULTS

At normobaric conditions, increasing the FiO2 from 0.4 (baseline) to 1.0 resulted in a significant increase in brain oxygen tension from 33 +/- 14 to 63 +/- 28 mmHg (P<0.05). Compared with baseline, both hyperbaric conditions (at an FiO2 of 1.0) led to a significant increase in brain oxygen tension to 151 +/- 65 mmHg (P<0.001) at 1.9 bar and to 294 +/- 134 mmHg (P<0.001) at 2.8 bar.

CONCLUSIONS

If there is a need for increased oxygenation in the brain, then one way to achieve this is to apply hyperbaric conditions at 100% oxygen. Compared with an atmospheric pressure with a FiO2 of 0.4, a nine-fold increase (900%) in PbrO2 values can be reached by increasing the FiO2 to 1.0 and the pressure to 2.8 bar. In this study, hyperbaric oxygen pressure in the brain did not lead to changes in intracranial pressure or in brain glucose/lactate levels.

Optimal dosing as a necessary condition for the efficacy of hyperbaric oxygen therapy in acute ischemic stroke: a critical review

The effectiveness of hyperbaric oxygen therapy (HBOT) in clinical and experimental acute ischemic stroke (AIS) has been controversial for many years. However, in the literature, no data was found on the dose/effect of HBOT in patients with AIS. We analyzed retrospectively the published data of clinical studies performed in different hyperbaric centers (a total of 265 patients). The dose of HBOT (DHBOT) was calculated considering the product intrabarochamber pO2 (ATA), the duration of a single HBOT exposure (hours), and the number of HBOT treatments. Efficacy of HBOT (EfHBOT) data regarding the number of patients who showed significant clinical improvement of their neurologic status in the course of the treatment HBOT (the percentage of the total number of patients). The level of EfHBOT in each study was compared with a corresponding value of DHBOT. A comparison of the data shows a pronounced tendency for higher values of EfHBOT as the level of the average values of the total DHBOT increases. The coefficient of correlation between these parameters appears to be fairly high (r = 0.92). The maximum possible value of EfHBOT is 100%, which corresponded to the average values of DHBOT at a level of no less than 30 agreed units. The examined data suggest that applying optimal total DHBOT may provide a maximum possible EfHBOT in treating patients with AIS.

Effects of hyperbaric oxygenation

OBJECT

Hyperbaric oxygenation (HBO) therapy has been shown to reduce mortality by 50% in a prospective randomized trial of severely brain injured patients conducted at the authors' institution. The purpose of the present study was to determine the effects of HBO on cerebral blood flow (CBF), cerebral metabolism, and intracranial pressure (ICP), and to determine the optimal HBO treatment paradigm.

METHODS

Oxygen (100% O2, 1.5 atm absolute) was delivered to 37 patients in a hyperbaric chamber for 60 minutes every 24 hours (maximum of seven treatments/patient). Cerebral blood flow, arteriovenous oxygen difference (AVDO2), cerebral metabolic rate of oxygen (CMRO2), ventricular cerebrospinal fluid (CSF) lactate, and ICP values were obtained 1 hour before and 1 hour and 6 hours after a session in an HBO chamber. Patients were assigned to one of three categories according to whether they had reduced, normal, or raised CBF before HBO. In patients in whom CBF levels were reduced before HBO sessions, both CBF and CMRO2 levels were raised 1 hour and 6 hours after HBO (p < 0.05). In patients in whom CBF levels were normal before HBO sessions, both CBF and CMRO2 levels were increased at 1 hour (p < 0.05), but were decreased by 6 hours after HBO. Cerebral blood flow was reduced 1 hour and 6 hours after HBO (p < 0.05), but CMRO2 was unchanged in patients who had exhibited a raised CBF before an HBO session. In all patients AVDO2 remained constant both before and after HBO. Levels of CSF lactate were consistently decreased 1 hour and 6 hours after HBO, regardless of the patient's CBF category before undergoing HBO (p < 0.05). Intracranial pressure values higher than 15 mm Hg before HBO were decreased 1 hour and 6 hours after HBO (p < 0.05). The effects of each HBO treatment did not last until the next session in the hyperbaric chamber.

CONCLUSIONS

The increased CMRO2 and decreased CSF lactate levels after treatment indicate that HBO may improve aerobic metabolism in severely brain injured patients. This is the first study to demonstrate a prolonged effect of HBO treatment on CBF and cerebral metabolism. On the basis of their data the authors assert that shorter, more frequent exposure to HBO may optimize treatment.

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

OBJECT

Hyperbaric oxygenation (HBO) therapy has been shown to reduce mortality by 50% in a prospective randomized trial of severely brain injured patients conducted at the authors' institution. The purpose of the present study was to determine the effects of HBO on cerebral blood flow (CBF), cerebral metabolism, and intracranial pressure (ICP), and to determine the optimal HBO treatment paradigm.

METHODS

Oxygen (100% O2, 1.5 atm absolute) was delivered to 37 patients in a hyperbaric chamber for 60 minutes every 24 hours (maximum of seven treatments/patient). Cerebral blood flow, arteriovenous oxygen difference (AVDO2), cerebral metabolic rate of oxygen (CMRO2), ventricular cerebrospinal fluid (CSF) lactate, and ICP values were obtained 1 hour before and 1 hour and 6 hours after a session in an HBO chamber. Patients were assigned to one of three categories according to whether they had reduced, normal, or raised CBF before HBO. In patients in whom CBF levels were reduced before HBO sessions, both CBF and CMRO2 levels were raised 1 hour and 6 hours after HBO (p < 0.05). In patients in whom CBF levels were normal before HBO sessions, both CBF and CMRO2 levels were increased at 1 hour (p < 0.05), but were decreased by 6 hours after HBO. Cerebral blood flow was reduced 1 hour and 6 hours after HBO (p < 0.05), but CMRO2 was unchanged in patients who had exhibited a raised CBF before an HBO session. In all patients AVDO2 remained constant both before and after HBO. Levels of CSF lactate were consistently decreased 1 hour and 6 hours after HBO, regardless of the patient's CBF category before undergoing HBO (p < 0.05). Intracranial pressure values higher than 15 mm Hg before HBO were decreased 1 hour and 6 hours after HBO (p < 0.05). The effects of each HBO treatment did not last until the next session in the hyperbaric chamber.

CONCLUSIONS

The increased CMRO2 and decreased CSF lactate levels after treatment indicate that HBO may improve aerobic metabolism in severely brain injured patients. This is the first study to demonstrate a prolonged effect of HBO treatment on CBF and cerebral metabolism. On the basis of their data the authors assert that shorter, more frequent exposure to HBO may optimize treatment.

Hyperbaric oxygen reduces infarct volume in rats by increasing oxygen supply to the ischemic periphery

OBJECTIVE

Hyperbaric oxygen (HBO) increases oxygen supply to anoxic areas. To examine the therapeutic effect of HBO on ischemic stroke, we measured infarct volume as well as cerebral blood flow (CBF), oxygen supply, and lipid peroxidation in the ischemic periphery.

DESIGN

Prospective experimental study in rats.

SETTING

Experimental laboratory in a university teaching hospital.

SUBJECTS

Thirty-eight adult rats.

INTERVENTION

The rats were anesthetized (1% halothane) and intubated. Focal ischemia was induced by ligating the right middle cerebral and right common carotid arteries. Nineteen animals were exposed to 2 hrs of HBO (100% oxygen, 3 atmospheres absolute), initiated 10 mins after the onset of ischemia. The remaining animals were kept at ambient pressure and used as controls.

MEASUREMENTS AND MAIN RESULTS

At the initiation of ischemia, CBF measured by a laser-Doppler flow probe placed in the ischemic periphery was reduced to 47%+/-11% and 51%+/-15% of normal levels in animals exposed or not to HBO, respectively. These altered values were not affected further by administration of HBO and remained stable throughout a 2-hr observation period. Arterial oxygen pressure and content were significantly increased to 1571+/-130 torr (209.41+/-17.32 kPa; p < .0001) and 1.03+/-0.04 mmol/dL (p < 0.0001), respectively, in HBO-treated animals compared with nontreated animals (139+/-14 torr [18.53+/-1.87 kPa] and 0.86+/-0.04 mmol/dL, respectively). The calculated increase in the oxygen supply to the ischemic periphery was 20%. The infarct volume of HBO-treated animals measured 24 hrs after the onset of focal cerebral ischemia was significantly reduced by 18% (HBO-treated, 132+/-13 mm3 vs. nontreated, 161+/-29 mm3; p = .02). Lipid peroxidation was unchanged after 120 mins of HBO administration in the cerebral cortex where the laser-Doppler flow probe was placed.

CONCLUSIONS

HBO at 3 atmospheres absolute reduced infarct volume by increasing oxygen supply to the ischemic periphery without aggravating lipid peroxidation, suggesting that HBO can be useful in treating stroke victims.

Effects of hyperbaric oxygen on neurologic outcome for cerebral ischemia in rats

OBJECTIVE

To evaluate the effect of hyperbaric oxygen (HBO) therapy on neurologic outcome (assessed by the quantal bioassay approach) following acute focal cerebral ischemia in rats.

METHODS

Two separate experimental trials were conducted. Trial 1, a nonblinded experiment, used 38 rats. Trial 2, a blinded experiment, used 59 rats. Focal cerebral ischemia was induced with a surgically placed intraluminal occlusion of the left middle cerebral artery; subsequent removal allowed reperfusion. Arterial occlusion times were varied from 5 to 90 minutes in trial 1, and from 3 to 45 minutes in trial 2. The control groups were maintained at ambient pressure for the duration of each trial. The trial 1 treatment group received a single 30-minute HBO treatment at 2.0 atmospheres absolute (ATA) on the initial day of ischemia. The trial 2 treatment group received 30-minute HBO treatments at 2.0 ATA daily for 4 consecutive days. The animals underwent daily 5-point neurologic examinations. A computerized quantal bioassay was used to determine the ET50--the occlusion time required to cause a neurologic abnormality in half of the animals. The control and treatment ET50 values were compared in each trial using a 2-tailed t-test. An increased ET50 for the treatment vs the control group implied a beneficial effect of HBO; a decrease, the opposite. The study had a power of 80% to detect a difference of 11.4 minutes in the ET50 for a 2-sided alpha = 0.05.

RESULTS

For trial 1: the HBO ET50 was 18.1 +/- 21.9 minutes and the control ET50 was 22.8 +/- 25.0 minutes (p > 0.2). For trial 2: the HBO ET50 was 9.49 +/- 17.4 minutes and the control ET50 was 14.9 +/- 14.2 minutes (p < 0.2).

CONCLUSION

HBO therapy showed no apparent benefit in a rat model as a treatment modality for acute cerebral ischemia with reperfusion.

Repeated hyperbaric oxygen induces ischemic tolerance in gerbil hippocampus

Hyperbaric oxygen (HBO; 100% oxygen at 2 atmospheres absolute) was administered for 1 h to male Mongolian gerbils either for a single session or every other day for five sessions. Two days after HBO pretreatment, the gerbils were subjected to 5 min of forebrain ischemia by occlusion of both common carotid arteries under anesthesia. Seven days after recirculation, neuronal density per 1-mm length of the CA1 sector in the hippocampus was significantly better preserved in the five-session HBO pretreatment group (n = 10: 175.7 (47.8/mm, 54.9% of normal) than in the ischemic control group (n = 10: 26.2 (11.6/mm, 8.0% of normal) and in the single-session HBO pretreatment group (n = 7: 37.3 (21.7/mm, 11.4% of normal). Immunohistochemical staining for the 72-kDa heat-shock protein (HSP-72) in the CA1 sector performed 2 days following pretreatment revealed that the five-session HBO pretreatment increased the amount of HSP-72 present compared with that in the ischemic control group and in the single HBO pretreatment group. These results suggest that tolerance against ischemic neuronal damage was induced by repeated HBO pretreatment, which is thought to occur through the induction of HSP-72 synthesis.

A pilot study of hyperbaric oxygen in the treatment of human stroke

We administered hyperbaric oxygen or air in a double-blind prospective protocol to 39 patients with ischemic cerebral infarction. We interrupted the study when we noticed what appeared to be a trend favoring the air-treated patients, whose neurological deficits were less severe (mean +/- SEM score on graded neurological examination: air, 25.6 +/- 4.9; oxygen, 34.5 +/- 7.5) and whose infarcts were smaller (air, 29.0 +/- 12.2 cm3; oxygen, 49.2 +/- 11.7 cm3) at 4 months. The trend, we decided, was probably an artifact of the randomization process. Nevertheless, we chose not to resume the trial because the treatment was difficult to administer by schedule (for various reasons the treatment protocol was broken in 15 of the 39 patients), was poorly tolerated (eight of the 39 patients refused to continue treatments), and did not produce dramatic improvement.

The effect of hyperbaric oxygen on glucose utilization in a freeze-traumatized rat brain

Local cerebral glucose utilization was measured with the autoradiographic 2-deoxyglucose technique in rats injured by a focal parietal cortical freeze lesion then treated with hyperbaric oxygen (HBO). The cold lesion depressed glucose utilization in the contralateral as well as in the ipsilateral hemisphere. The largest decreases were observed in ipsilateral cortical areas. Treatment of lesioned animals with HBO at 2 atm for 90 minutes on each of 4 consecutive days tended to increase the overall cerebral glucose utilization measured 5 days after injury when compared to animals exposed to normobaric air. This improvement reached statistical significance in five of the 21 structures studied: the auditory cortex, medial geniculate body, superior olivary nucleus, and lateral geniculate body ipsilateral to the lesion, and the mammillary body. The data indicate that changes in lesioned rats exposed to HBO are not restricted to the period of time that the animals are in the hyperbaric chamber but are persistent.

Ameliorating effects of hyperbaric oxygenation on experimental allergic encephalomyelitis

The effect of hyperbaric oxygenation (OHP) on survival and quality of survival of guinea pigs afflicted with experimental allergic encephalomyelitis (EAE) was investigated. EAE was induced in Hartley and Strain 13 animals by intradermal injections of whole guinea pig spinal cord in complete Freund's adjuvant. The inoculated animals were divided into control and treatment groups; the treated animals received OHP in a variety of treatment schedules. Clinical signs of EAE were quantitated and mean survival times were measured. When Hartley animals were exposed to 100% O2 at 2.5 atmospheres absolute (ATA) for 2 hr/day from 5--19 days postinoculation, the mean survival time (+/- SE) was 19.1 +/- 1.6 days relative to 15.7 +/- 0.7 days in the control (p less than 0.050). When Strain 13 guinea pigs were treated with 100% O2 at 2ATA for 4 hr/day on 5--16 days, the mean survival time was 21.6 +/- 0.6 days compared to 16.0 +/- 0.4 days for the control (p less than 0.001). Clinical sign measurements demonstrated that the onset of EAE in the treated animals of both strains occurred between 4--6 days after these signs became detectable in control animals. These results suggest that OHP therapy can ameliorate EAE in afflicted guinea pigs.

Effects of hyperbaric oxygenation on cerebral vasomotor tone in acute intracranial hypertension: an experimental study

The effects of hyperbaric oxygenation with 2 atm. pressure and 100 percent oxygen on cerebrovascular tone were assessed by the reactivity of the cerebral vessels to CO2 and vasomotor capacitance index (the cranial pressure divided by the mean arterial pressure) in 50 anaesthetized artifically ventilated dogs, in which intracranial pressure was raised by slow inflation of an extradural balloon. Hyperbaric oxygenation reduced the intracranial pressure only at the stage when the cerebral vessels were still responsive to CO2, as indicated by a rise in intracranial pressure of 30-70 mmHg; under these circumstances, both the reactivity of CO2 and the vasoconstrictor tone of cerebral vessels were improved by hyperbaric oxygenation. At this stage, rapid decrease of the intracranial pressure produced by deflation of the extradual balloon showed no rebound, and hyperbaric oxygenation rapidly restored the vasomotor tone. When CO2 failed to influence the intracranial pressure of about 100 mmHg hyperbaric oxygenation did not aid the recovery of the reactivity of the cerebral vessels to CO2 or the vasoconstrictor tone. In extreme intracranial hypertension (above 100 mmHg) when there was reactivity to CO2 and the electroencephalogram was flat, rapid balloon deflation was followed by a further gradual increase of intracranial pressure and hyperbaric oxygenation did not restore the cerebrovascular tone. The effect of hyperbaric oxygenation in experimental intracranial hypertension appeared to be dependent upon the vasoconstrictor tone of the cerebral vessels, which would be indicated by a vasodilator response to CO2.

Response of cereborspinal fluid pressure to hyperbaric oxygenation

The response of cerebrospinal fluid pressure (CSFP) to hyperbaric oxygenation (OHP) was investigated in 13 patients with acute cerebral damage and in dogs with or without experimentally produced cerebral damage. To elucidate the mechanism of the CSFP response, continuous measurements of carotid blood flow, arterial blood pressure, central venous pressure, and superior sagittal sinus pressure and CSFP were made before, during and after OHP. There was considerable variation in the response of CSFP to OHP in the patients, but three main patterns emerged; type I (nine cases), CSFP decreased at the beginning and rose again at the end of OHP, type II (two cases), CSFP fell with OHP and remained significantly lower than pretreatment level after it, and type III (two cases), CSFP showed little change with OHP. An animal without cerebral damage commonly showed a type I response of CSFP to OHP; the changes of CSFP at the beginning and end of OHP are mainly due to the changes of the cerebral blood flow. There may be two different actions of OHP on cerebral oedema, one decreasing cerebral oedema and another (mainly affecting the normal brain) producing cerebral oedema. Information obtained from the response of CSFP to OHP may be useful in judging the severity and pathophysiological state of cerebral damage.

Effects of hyperbaric oxygen on intracranial pressure and cerebral blood flow in experimental cerebral oedema

Increased intracranial pressure was induced in anaesthetized dogs by application of liquid nitrogen to the dura mater. Intracranial pressure and cerebral blood flow were measured, together with arterial blood pressure and arterial and cerebral venous blood gases.Carbon dioxide was administered intermittently to test the responsiveness of the cerebral circulation, and hyperbaric oxygen was delivered at intervals in a walk-in hyperbaric chamber, pressurized to two atmospheres absolute.Hyperbaric oxygen caused a 30% reduction of intracranial pressure and a 19% reduction of cerebral blood flow in the absence of changes in arterial PCO(2) or blood pressure, but only as long as administration of carbon dioxide caused an increase in both intracranial pressure and cerebral blood flow. When carbon dioxide failed to influence intracranial pressure or cerebral blood flow then hyperbaric oxygen had no effect. This unresponsive state was reached at high levels of intracranial pressure.