Cerebral resuscitation after cardiac arrest using hetastarch hemodilution, hyperbaric oxygenation and magnesium ion

Hyperbaric oxygen therapy in acute stroke: is it time for Justitia to open her eyes?

Hypoxia is a critical component of neuronal death in patients with stroke. Therefore increasing oxygenation of brain tissue seems to be a logical therapy against cerebral ischemia. Oxygen therapy exists in two modalities: normobaric hyperoxia therapy and hyperbaric oxygen therapy (HBO). HBO is a therapeutic procedure in which pure (100%) oxygen is administered at greater than atmospheric pressure in HBO therapy chambers. In this review article, we aimed to summarize the current knowledge regarding the therapeutic use of HBO in acute stroke patients. Literature review and electronic search were performed using PubMed, Medscape, and UpToDate with the keywords stroke, acute stroke, hyperbaric oxygen therapy, and hyperoxia. According to the reviewed literature, the use of HBO as routine stroke therapy cannot be justified in acute stage of stroke. More randomized, controlled studies are needed regarding safety and especially effectives of HBO in stroke patients. Also, standardized definitionof HBO should be proposed and used in all future studies.

Neuroprotection by oxygen in acute transient focal cerebral ischemia is dose dependent and shows superiority of hyperbaric oxygenation

The neuroprotective effect of oxygen after acute stroke in rats has been shown previously. However, the question of optimal dosing still remains unanswered. Thus, we investigated the use of oxygen at different concentrations by either normobaric oxygenation (NBO) or hyperbaric oxygenation (HBO) at different pressures in a model of transient ischemia/reperfusion in rats. Animals underwent 90 min of middle cerebral artery occlusion (MCAO) followed by 90 min of reperfusion before oxygen treatment. Oxygen was applied either by NBO (100% O(2); 1.0 absolute atmosphere, ATA) or HBO (100% O(2); 1.5, 2.0, 2.5 or 3.0 ATA) for 1 h. Primary endpoints were infarct volume and clinical outcome measured 24 h and 7 days following the MCAO. A statistically significant and long-lasting reduction in infarct volume was seen in the HBO 2.5 ATA and 3.0 ATA groups over a period of 7 days. The reduced infarct volume was accompanied with a statistically significant improvement in clinical outcome in the high-dose oxygen-treated groups. The presented data indicate that oxygen is a highly neuroprotective molecule in transient focal cerebral ischemia in rats, when applied early and at high doses. The effect is dose dependent and shows a superiority of HBO over NBO, when the primary endpoints infarct volume reduction and clinical outcome are analyzed. These data are important for the development of new acute stroke treatment studies in humans.

Therapeutic Window for Use of Hyperbaric Oxygenation in Focal Transient Ischemia in Rats

Background and Purpose— Hyperbaric oxygenation (HBO) is an attractive procedure that has been used frequently in cerebral ischemia. However, depending on the model of cerebral ischemia and HBO protocol, different and conflicting results were obtained in the past. This study was undertaken to reevaluate the effects of single administration of HBO in 2 models of acute cerebral ischemia: transient or permanent focal ischemia in rats. A comparison of the 2 ischemia models was undertaken to search for a putative therapeutic window.

Methods— The intraluminal middle cerebral artery occlusion model (MCAO) was used. The effect of single HBO therapy (3 atm absolute, 60 minutes) on transient or permanent focal ischemia, when applied at different times (3, 6, or 12 hours) after MCAO, was investigated; infarct volume and neurological deficits were assessed at 24 hours and up to 7 days.

Results— HBO had neuroprotective effects on transient MCAO when HBO was initiated within the first 6 hours, while it aggravated the ischemic injury histologically and clinically when initiated 12 hours after MCAO. In permanent MCAO, HBO did not reduce tissue damage regardless of the timing of therapy.

Conclusions— HBO is highly efficient in reducing infarct volume and improving neurobehavioral outcome in transient MCAO within the first 6 hours. HBO at later time points (≥12 hours) is harmful by increasing infarct volume. In permanent MCAO, HBO failed to improve infarct volume and clinical outcome.

Non-pharmacologic (physiologic) neuroprotection in the treatment of brain ischemia

Clinical trials for ischemic stroke have been characterized by a disappointing series of negative results, using a panoply of pharmacologic agents. This paper emphasizes five physiologic measures that can be taken to mitigate ischemic brain damage. These are (1) hypothermia, (2) insulin, (3) arterial hyperoxemia, (4) blood pressure control and (5) magnesium. Hypothermia is protective in both focal and global ischemia, even postischemically protecting against selective neuronal necrosis and infarction. The total equation for protection includes the (i) postischemic delay, (ii) depth, and (iii) duration of hypothermia. Insulin operates by lowering glucose levels to the normal range in focal ischemia. It is possible that very low glucose levels are detrimental in focal ischemia with paradoxical augmentation of the infarct size, and that spreading depression plays a role in this. Controlled arterial hyperoxemia seems effective experimentally in reducing infarct size, operating mechanistically by either a direct effect of oxygen, or vasoconstriction causing shunting of blood into the infarct, or both. Blood pressure is a critical determinant of infarct size, and raising blood pressure improves collateral blood flow and reduces stroke size. To be used clinically, however, hemorrhage must be ruled out. The most dramatic clinical effects of blood pressure are seen in aneurysm patients with vasospasm, where minor increases in blood pressure reverse temporary hemiparesis by reducing ischemia. Magnesium is likely the safest NMDA antagonist, with a long history of safe administration to pregnant women with eclampsia. There is potential interaction with insulin, in that magnesium causes hyperglycemia, which requires insulin to counteract it. Magnesium and insulin together have been shown effective in experimental brain ischemia. In the absence of safe and effective pharmacologic neuroprotection agents, clinical trials should be designed and launched to test these physiologic measures, singly and in combination, to reduce brain damage after ischemia.

Effect of hyperbaric oxygen therapy on survival after global cerebral ischemia in rats

BACKGROUND

Hyperbaric oxygenation (HBO) has been considered for many years for the treatment of severe brain ischemia. However, its efficacy has not been proven. The aim of this study was to shed light on this question.

METHODS

Acute global cerebral ischemia was induced in 18 rats using the four-vessel occlusion model. Regional cerebral blood flow (CBF) was determined by laser-Doppler flowmetry using a flexible 1 mm fiberoptic probe. Two stainless steel screws were used to measure the spontaneous electrical activity from the contralateral hemisphere. After ischemia monitored by laser-Doppler flowmetry and ECoG, the animals were divided into two groups: (1) control animals that breathed air at atmospheric pressure and (2) rats exposed to HBO at three atmospheres absolute pressure (ATA) for 1 hour. Survival time and rate were recorded for both groups of animals for 14 days.

RESULTS

The survival rate in the study group was significantly higher (45%) than in the control group (0%). In the animals that did not survive the 14-day period, those exposed to HBO survived longer than the control animals (59.8+/-9.1 hour versus 17.9+/-2.7 hours, p < 0.05).

CONCLUSION

This investigation demonstrates that HBO administered after global cerebral ischemia can increase survival in a rat stroke model.

Hyperbaric oxygen after global cerebral ischemia in rabbits reduces brain vascular permeability and blood flow

BACKGROUND AND PURPOSE

Hyperbaric oxygen (HBO) has been advocated as a therapy to improve neurological recovery after ischemia, since HBO may improve tissue oxygen delivery. We examined the effect of HBO treatment after global cerebral ischemia on early brain injury.

METHODS

Rabbits were subjected to 10 minutes of global cerebral ischemia by cerebrospinal fluid compression. After 30 minutes of reperfusion, rabbits either were subjected to HBO for 125 minutes and then breathed 100% O2 at ambient pressure for 90 minutes or breathed 100% O2 for 215 minutes. At the end of reperfusion and 90 minutes after exposure, brain vascular permeability and cerebral blood flow were measured. Somatosensory evoked potentials were monitored throughout the experiment.

RESULTS

HBO treatment reduced (P < .05) brain vascular permeability by 16% in gray matter and by 20% in white matter. Cerebral blood flow was lower (P < .05) in the HBO group (40.9 +/- 1.9 mL/min per 100 g, mean +/- SEM) compared with controls (50.8 +/- 2.0 mL/min per 100 g). Somatosensory evoked potential recovery was similar in the two groups (P > .05).

CONCLUSIONS

HBO administered after global cerebral ischemia promoted blood-brain barrier integrity. HBO treatment also reduced cerebral blood flow; this effect was not associated with a reduction in evoked potential recovery. Since neurological outcome after global cerebral ischemia is generally poor and treatment options are limited, HBO should be further investigated as a potential therapy.

Hyperbaric oxygen after global cerebral ischemia in rabbits does not promote brain lipid peroxidation

OBJECTIVE

To determine whether hyperbaric oxygen administered immediately after global cerebral ischemia increases free radical generation and lipid peroxidation in the brain or alters neurophysiologic recovery.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Animal research laboratory.

SUBJECTS

Adult male New Zealand white rabbits.

INTERVENTIONS

Anesthetized rabbits were subjected to 10 mins of global cerebral ischemia by infusing a mock cerebrospinal fluid into the subarachnoid space and increasing intracranial pressure equal to mean arterial pressure. Immediately upon reperfusion, one group of rabbits (n = 9) was treated with hyperbaric oxygen at 2.8 atmospheres absolute for 75 mins while the control group (n = 9) breathed room air for an equivalent period of time. At the end of the reperfusion period, oxyradical brain damage was determined by measuring brain levels of oxidized and total glutathione and free malondialdehyde. Neurophysiologic brain injury was assessed with cortical somatosensory evoked potentials.

MEASUREMENTS AND MAIN RESULTS

Both oxidized glutathione and the ratio of oxidized glutathione to reduced glutathione (total minus oxidized) were higher (p < .05) in the hyperbaric oxygen group, indicating that hyperbaric oxygen increased free radical generation. Nonetheless, brain malondialdehyde content, an index of lipid peroxidation, was similar (p > .05) in the two groups. Cortical somatosensory evoked potential recovery at the end of reperfusion was 50% higher (p < .05) in the hyperbaric oxygen-treated animals compared with controls.

CONCLUSIONS

Treatment with hyperbaric oxygen after ischemia increased the amount of oxygen free radicals in the brain. However, this increase in free radical generation was not associated with an increase in lipid peroxidation or a reduction in neurophysiologic recovery when measured after 75 mins of recirculation. These results suggest that hyperbaric oxygen administered immediately after global ischemia does not promote early brain injury.

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.

Effects of elevated plasma magnesium versus calcium on cerebral ischemic injury in rats

Both Mg2+ and Ca2+ have been implicated as having roles in the pathomechanisms of cerebral ischemia. To further study the effects of these ions on postischemic histologic outcome, fasted rats were given one of three intravenous infusions: 5.0 mmol/kg MgCl2, 5.0 mmol/kg MgCl2 + 0.035 units/kg regular insulin, or 1.0 mmol/kg CaCl2. This resulted in elevated plasma Mg2+ or Ca2+ concentrations in the corresponding groups. A fourth group received 0.9% NaCl (saline). Preinfusion plasma glucose concentration was similar for all groups and was unchanged after infusion in rats receiving either saline or MgCl2 + insulin. In contrast, postinfusion glucose concentration was increased in the MgCl2 group (p less than 0.001) and decreased in the CaCl2 group (p less than 0.001) relative to saline-treated rats. Following respective infusions, all rats underwent 10 minutes of reversible forebrain ischemia (bilateral carotid artery occlusion and systemic hypotension) followed by 7 days' recovery. Six of 12 CaCl2-treated rats died 2-3 days after ischemia; all other rats remained neurologically indistinguishable, without gross neurologic deficits. Histologic injury in the neocortex and caudate was moderate in all groups. In the hippocampus, MgCl2 + insulin resulted in 66 +/- 6% (mean +/- SD) dead CA1 pyramidal cells, which was similar to the amount in saline-treated rats (68 +/- 10%). Injury was increased in the MgCl2 group (79 +/- 4% dead cells), while in surviving CaCl2-treated rats, injury was decreased (54 +/- 13%). We conclude that the increased injury in MgCl2-treated rats and the decreased injury noted in surviving rats receiving CaCl2 are due to the plasma glucose concentrations present prior to ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain resuscitation and protection

No drug that is used for brain protection after global brain ischaemia as a result of cardiac arrest has been shown to be of benefit. Barbiturate agents have been proved not to be beneficial whereas studies of calcium-channel blocking drugs are inconclusive. Hypothermia, haemodilution and mechanical hyperventilation are not of proven benefit. Immediate defibrillation with rapid restoration of blood pressure is the best method to improve the neurological outcome after a cardiac arrest. After severe head injury, prompt emergency care to restore ventilation, oxygenation and blood pressure improves the neurological outcome. The early evacuation of extracerebral intracranial haematomas also improves the outcome. Corticosteroid therapy does not improve the outcome. The monitoring of intracranial pressure and the control of increased intracranial pressure by hyperventilation, cerebrospinal-fluid drainage and mannitol, frusemide and barbiturate therapy appear to improve the outcome after a severe head injury, although this has not been proved by randomized controlled studies.