Effect on biochemical markers of brain injury of therapy with deferoxamine or superoxide dismutase following cardiac arrest

Precision Cardiac Arrest Resuscitation Based on Etiology

Cardiac arrest results from a broad range of etiologies that can be broadly grouped as sudden and asphyxial. Animal studies point to differences in injury pathways invoked in the heart and brain that drive injury and outcome after these different forms of cardiac arrest. Present guidelines largely ignore etiology in their management recommendations. Existing clinical data reveal significant heterogeneity in the utility of presently employed resuscitation and postresuscitation strategies based on etiology. The development of future neuroprotective and cardioprotective therapies should also take etiology into consideration to optimize the chances for successful translation.

Metalloporphyrins as therapeutic catalytic oxidoreductants in central nervous system disorders

SIGNIFICANCE

Metalloporphyrins, characterized by a redox-active transitional metal (Mn or Fe) coordinated to a cyclic porphyrin core ligand, mitigate oxidative/nitrosative stress in biological systems. Side-chain substitutions tune redox properties of metalloporphyrins to act as potent superoxide dismutase mimics, peroxynitrite decomposition catalysts, and redox regulators of transcription factor function. With oxidative/nitrosative stress central to pathogenesis of CNS injury, metalloporphyrins offer unique pharmacologic activity to improve the course of disease.

RECENT ADVANCES

Metalloporphyrins are efficacious in models of amyotrophic lateral sclerosis, Alzheimer's disease, epilepsy, neuropathic pain, opioid tolerance, Parkinson's disease, spinal cord injury, and stroke and have proved to be useful tools in defining roles of superoxide, nitric oxide, and peroxynitrite in disease progression. The most substantive recent advance has been the synthesis of lipophilic metalloporphyrins offering improved blood-brain barrier penetration to allow intravenous, subcutaneous, or oral treatment.

CRITICAL ISSUES

Insufficient preclinical data have accumulated to enable clinical development of metalloporphyrins for any single indication. An improved definition of mechanisms of action will facilitate preclinical modeling to define and validate optimal dosing strategies to enable appropriate clinical trial design. Due to previous failures of "antioxidants" in clinical trials, with most having markedly less biologic activity and bioavailability than current-generation metalloporphyrins, a stigma against antioxidants has discouraged the development of metalloporphyrins as CNS therapeutics, despite the consistent definition of efficacy in a wide array of CNS disorders.

FUTURE DIRECTIONS

Further definition of the metalloporphyrin mechanism of action, side-by-side comparison with "failed" antioxidants, and intense effort to optimize therapeutic dosing strategies are required to inform and encourage clinical trial design.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Evaluation of gonadotrophin insufficiency in thalassemic boys with pubertal failure: spontaneous versus provocative test

The objective of this study was to determine whether iron toxicity in blood transfusion dependent beta-thalassemic patients with pubertal failure was associated with gonadotrophin (GTH) insufficiency as assessed by spontaneous and dynamic tests. Gonadotrophin-releasing-hormone (GnRH)-GTH secretory dynamics were studied by serial ultradian GTH profiles and a 100 microg i.v. GnRH bolus test (GBT) in 28 male beta-thalassemia major patients with failed puberty (FP group). Five healthy, non thalassemic prepubertal males were studied for comparative purposes. According to the pulse profile, patients in the FP group were subdivided into apulsatile (no FSH and LH pulses, n = 16; AFP group) and pulsatile (defective pulse profile, n = 12; PFP group) subsets. The FP group had lower basal FSH (p < 0.01), LH (p < 0.01) and GnRH stimulated FSH (p < 0.001) and LH levels (p < 0.001) than the controls. However, basal and GnRH-stimulated FSH (p < 0.01 for basal and p < 0.001 for peak) and LH (p < 0.01 for both basal and peak) levels were lower in the AFP than the PFP group. Serum ferritin levels in GnRH-non-responders were higher than those in the responders (9,052.63 +/- 579.14 mg/l vs 5,933.33 +/- 1,819.65 mg/l; p < 0.05). Similarly, symptomatic organ damage was higher in the AFP than the PFP patients (81% vs 42%; p < 0.001). In conclusion, this study suggests that iron overloaded thalassemic patients with failed puberty had abnormal GnRH-GTH secretory dynamics. The severity of the defect was heterogeneous, ranging from very severe (apulsatile) to less severe (pulsatile) subsets. Comparison between spontaneous and dynamic test levels showed that there was concordance between the degree of pulse defect and magnitude of LH response to GBT. However, ultradian GTH profile was a more reliable method for identifying the degree of GTH insufficiency than GBT. Our data also showed that iron toxicity was the major cause of GnRH-GTH deficiency in thalassemic patients. Such information may be useful for better understanding of the pathophysiology of hypogonadotrophic hypogonadism (HH), thereby promoting therapeutic options for induction of puberty and spermatogenesis.

Brain ischemia and reperfusion: molecular mechanisms of neuronal injury

Brain ischemia and reperfusion engage multiple independently-fatal terminal pathways involving loss of membrane integrity in partitioning ions, progressive proteolysis, and inability to check these processes because of loss of general translation competence and reduced survival signal-transduction. Ischemia results in rapid loss of high-energy phosphate compounds and generalized depolarization, which induces release of glutamate and, in selectively vulnerable neurons (SVNs), opening of both voltage-dependent and glutamate-regulated calcium channels. This allows a large increase in cytosolic Ca(2+) associated with activation of mu-calpain, calcineurin, and phospholipases with consequent proteolysis of calpain substrates (including spectrin and eIF4G), activation of NOS and potentially of Bad, and accumulation of free arachidonic acid, which can induce depletion of Ca(2+) from the ER lumen. A kinase that shuts off translation initiation by phosphorylating the alpha-subunit of eukaryotic initiation factor-2 (eIF2alpha) is activated either by adenosine degradation products or depletion of ER lumenal Ca(2+). Early during reperfusion, oxidative metabolism of arachidonate causes a burst of excess oxygen radicals, iron is released from storage proteins by superoxide-mediated reduction, and NO is generated. These events result in peroxynitrite generation, inappropriate protein nitrosylation, and lipid peroxidation, which ultrastructurally appears to principally damage the plasmalemma of SVNs. The initial recovery of ATP supports very rapid eIF2alpha phosphorylation that in SVNs is prolonged and associated with a major reduction in protein synthesis. High catecholamine levels induced by the ischemic episode itself and/or drug administration down-regulate insulin secretion and induce inhibition of growth-factor receptor tyrosine kinase activity, effects associated with down-regulation of survival signal-transduction through the Ras pathway. Caspase activation occurs during the early hours of reperfusion following mitochondrial release of caspase 9 and cytochrome c. The SVNs find themselves with substantial membrane damage, calpain-mediated proteolytic degradation of eIF4G and cytoskeletal proteins, altered translation initiation mechanisms that substantially reduce total protein synthesis and impose major alterations in message selection, down-regulated survival signal-transduction, and caspase activation. This picture argues powerfully that, for therapy of brain ischemia and reperfusion, the concept of single drug intervention (which has characterized the approaches of basic research, the pharmaceutical industry, and clinical trials) cannot be effective. Although rigorous study of multi-drug protocols is very demanding, effective therapy is likely to require (1) peptide growth factors for early activation of survival-signaling pathways and recovery of translation competence, (2) inhibition of lipid peroxidation, (3) inhibition of calpain, and (4) caspase inhibition. Examination of such protocols will require not only characterization of functional and histopathologic outcome, but also study of biochemical markers of the injury processes to establish the role of each drug.

Usual and unusual methods for detection of lipid peroxides as indicators of tissue injury in cerebral ischemia: what is appropriate and useful?

1. Free radical-dependent lipid peroxidation processes have long been thought to contribute to brain damage following stroke or cerebral ischemia/reperfusion. 2. The preponderance of evidence for this belief has been derived indirectly, through diminution of tissue injury indices (e.g., brain infarct volume) facilitated by application of free radical scavenger substances. 3. Direct, unequivocal evidence for lipid peroxidation in terms of classical assays (detection of conjugated diene absorbance or thiobarbituric acid-reactive substances) is considerably less common, and its validity can be questioned. 4. Correlations of treatment-induced diminishment of brain injury indices with reductions in lipid peroxidation level are rarer still. 5. Reasons underlying the disparity between the belief that lipid peroxidation contributes to ischemic brain injury and direct evidence for this contribution (at least acutely) are proposed, along with evidence that new methods are being developed which should provide the basis for obtaining a definitive answer.

Postischemic infusion of Cu/Zn superoxide dismutase or SOD:Tet451 reduces cerebral infarction following focal ischemia/reperfusion in rats

Oxygen-free radicals play a major role in neuronal cell injury following cerebral ischemia/reperfusion. The free-radical scavenging enzyme, Cu/Zn superoxide dismutase (SOD-1), ameliorates various types of brain injury resulting from temporary CNS ischemia. We have compared the cerebroprotective properties of human SOD-1 (hSOD-1) with a novel recombinant SOD-1 hybrid protein, SOD:Tet451, composed of hSOD-1 linked to the neuronal binding fragment of tetanus toxin (TTxC). Following 2 h of temporary middle cerebral artery occlusion, rats infused with equivalent activities of either hSOD-1 or SOD:Tet451 for the initial 3 h of reperfusion showed reductions in cerebral infarct volume of 43 and 57%, respectively, compared to saline-treated controls (P < 0.01). Serum hSOD-1 concentrations in rats receiving SOD:Tet451 were seven-fold higher than those in rats receiving the native enzyme. Animals treated with SOD:Tet451 also demonstrated an extended persistence of hSOD-1 in the bloodstream during drug washout as compared to animals given free enzyme. Immunohistochemical examination of brain sections from an SOD:Tet451-treated ischemic rat showed positive immunoreactivity in the ipsilateral cerebral cortex using either anti-TTxC or anti-human SOD-1 antibodies. Our results document that both hSOD-1 and SOD:Tet451 significantly reduce brain infarct volume in a model of transient focal ischemia/reperfusion in rats. Additionally, our findings suggest that the cerebroprotective effects of SOD-1 may be enhanced by neuronal targeting as seen with the hybrid protein SOD:Tet451.

Macroscopic indices of lipid peroxidation in cerebral ischemia/reperfusion: validity and sensitivity enhancement in terms of conjugated diene detection

Recent evidence for the occurrence of in vivo lipid peroxidation in the context of cerebral ischemia/reperfusion, as detected by classical tests such thiobarbituric acid reactivity and conjugated diene absorbance, is critically reviewed. Despite the widespread perception that lipid peroxidation is well-established and to be expected under such circumstances, in general these detection methods have not been applied with rigor sufficient to prove the quantitative existence of lipid peroxides unequivocally. The development of sensitive methods which can be utilized in small tissue samples at early times after brain injury is needed. In particular, the conditions necessary for the establishment of a more rigorous and sensitive method of conjugated diene detection in terms of difference spectral analysis are detailed and illustrated. In addition, a new autofluorescence in the far-ultraviolet region is shown to be associated with oxygenated conjugated diene-containing compounds.

Effect of superoxide dismutase on acute reperfusion injury of the rabbit brain

To study the involvement of free oxygen radicals of the blood-brain barrier (BBB) disruption during early reperfusion, we isolated the distal internal carotid artery, and the middle and anterior cerebral arteries via the transorbital approach in anesthetized rabbits. Using radiolabeled microspheres, regional cerebral blood flow (rCBF) was measured before, during and after 1-hour unilateral occlusion of these vessels. Fifty-five minutes after ischemia, animals received intravenous saline placebo (control), superoxide dismutase (SOD) at 8 mg/kg = 30,000 U/kg, or weakened superoxide dismutase (wSOD) at 8 mg/kg = 30,000 U/kg. Integrity of the BBB was assessed by leakage of Evan's Blue-albumin dye (EB-albumin dye), which was given at 15 minutes of reperfusion and allowed to circulate for an additional hour. In the control and wSOD-treated groups, rCBF decreased (26% and 40% of control, respectively) within the blue-tinted tissue of the occluded hemisphere during ischemia; hyperemia was observed during early reperfusion. In the control and wSOD-treated groups, EB-albumin dye leakage across the BBB increased 49% within the occluded hemisphere. However, within the SOD-treated group, the BBB showed minimal dye leakage even though rCBF of the occluded hemisphere (so-called blue-tinted tissue) decreased by 38% during ischemia. We conclude that 1-hour focal cerebral ischemia and reperfusion produce a vascular endothelial injury at the BBB. Since SOD administration showed significant protection, free-oxygen-radical production during early reperfusion is associated with breakdown of the BBB to large molecules.

Brain injury and repair mechanisms: the potential for pharmacologic therapy in closed-head trauma

Rotational acceleration from closed-head trauma produces shear-strain brain injury at the interface of gray and white matter. The initial injury is followed by progressive damage involving three key phenomena: progression of subtle focal axonal damage to axonal transection between six and 12 hours after injury, progressive development of tissue microhemorrhages between 12 and 96 hours after injury, and development of tissue and cerebral spinal fluid lactic acidosis that does not appear to be explained by trauma-induced tissue depolarization, activation of phospholipases and the release of free arachidonic acid, radical generation by metabolism of arachidonate, and lipid peroxidation with consequent membrane degradation and partial mitochondrial uncoupling. Because of terminal differentiation, neurons may have a limited membrane repair capability that might be stimulated by growth factors. Other potential therapeutic interventions include calmodulin inhibitors, iron chelators, and free radical scavengers.

Fluorescent histochemical localization of lipid peroxidation during brain reperfusion following cardiac arrest

Rats were subjected to cardiac arrest and resuscitation, 90 min of reperfusion, and in situ perfusion fixation. Thiobarbituric acid (TBA) was included in the aldehyde-free perfusion fixative, the TBA reaction was driven in situ by heating, and fluorescence microscopy was utilized to characterize the location of products of the TBA reaction. Absorbance-difference spectra were performed on butanol-extracted brain homogenates to confirm in situ formation of TBA adducts with aldehydic products of lipid peroxidation. Nissl-stained sections revealed good cellular fixation without shrinkage artifacts. Fluorescence was not seen microscopically when TBA was omitted from the perfusion fixative, and little fluorescence was present in normal brains or brains after ischemia only. However, after 90-min reperfusion, intense granular fluorescence was seen in the neuronal perikarya (especially at the base of the apical dendrite) of numerous pyramidal neurons in cortical layers 5 and 6 and in the pyramidal layer of Ammon's horn in the hippocampus. The nuclei of these cells exhibited no fluorescence. Fluorescence was also present in some striatal neurons, but was absent in the adjacent radial bundles. Neither glia nor white matter exhibited similar fluorescence. These observations indicate that neurons in the selectively vulnerable zones of the cortex and hippocampus are early and specific targets of lipid peroxidation during post-ischemic reperfusion.

Cerebral resuscitation after cardiac arrest: research initiatives and future directions

At present, fewer than 10% of cardiopulmonary resuscitation (CPR) attempts prehospital or in hospitals outside special care units result in survival without brain damage. Minimizing response times and optimizing CPR performance would improve results. A breakthrough, however, can be expected to occur only when cerebral resuscitation research has achieved consistent conscious survival after normothermic cardiac arrest (no flow) times of not only five minutes but up to ten minutes. Most cerebral neurons and cardiac myocytes tolerate normothermic ischemic anoxia of up to 20 minutes. Particularly vulnerable neurons die, in part, because of the complex secondary post-reflow derangements in vital organs (the postresuscitation syndrome) which can be mitigated. Brain-orientation of CPR led to the cardiopulmonary-cerebral resuscitation (CPCR) system of basic, advanced, and prolonged life support. In large animal models with cardiac arrest of 10 to 15 minutes, external CPR, life support of at least three days, and outcome evaluation, the numbers of conscious survivors (although not with normal brain histology) have been increased with more effective reperfusion by open-chest CPR or emergency cardiopulmonary bypass, an early hypertensive bout, early post-arrest calcium entry blocker therapy, or mild cerebral hypothermia (34 C) immediately following cardiac arrest. More than ten drug treatments evaluated have not reproducibly mitigated brain damage in such animal models. Controlled clinical trials of novel CPCR treatments reveal feasibility and side effects but, in the absence of a breakthrough effect, may not discriminate between a treatment's ability to mitigate brain damage in selected cases and the absence of any treatment effect. More intensified, coordinated, multicenter cerebral resuscitation research is justified.

Brain mitochondrial DNA is not damaged by prolonged cardiac arrest or reperfusion

Postischemic reperfusion is known to cause iron-mediated peroxidation of polyunsaturated fatty acids in membranes, including mitochondrial membranes, in the brain cortex. Consequently, we tested the hypothesis that this radical-mediated damage would extend to DNA. Mitochondrial DNA (mtDNA) was chosen because of its presence at a known site of free radical formation, its sensitivity and ease of assay, and its known lack of any repair systems. In model experiments we utilized endonuclease III or piperidine to amplify topological form conversions in mtDNA damaged by in vitro reactions with hydroxyl radical. We then applied the amplified detection assays to dog brain mtDNA isolated after 2 or 8 h of reperfusion following a 20-min cardiac arrest. We found that ischemia and reperfusion caused no topological form conversions in mtDNA. Similarly, nucleotide incorporation by a gap-filling reaction showed no sensitivity to digestion of the mtDNA by exonuclease III, an enzyme known to remove blocked 3' termini at the site of radical-generated nicks. Furthermore, the recovery of mtDNA was similar in all experimental groups, suggesting that putatively damaged forms had not been removed by rapid degradation. Thus, despite mitochondrial membrane damage, brain mtDNA does not accumulate oxygen radical damage during postischemic brain reperfusion.

Assessment of free radical-induced damage in brain proteins after ischemia and reperfusion

Brain damage initiated during global ischemia has been shown to be exacerbated by iron-dependent lipid peroxidation during early reperfusion. We hypothesized that other cellular components might be involved in similar free radical reactions. In this study we examined three brain protein fractions and ribosomal RNA for evidence of free radical damage during post-ischemic reperfusion. Global brain ischemia was induced by 20-min cardiac arrest. Dogs were divided into four groups: (1) non-ischemic controls; (2) 20-min cardiac arrest without reperfusion; (3) 20-min cardiac arrest and 2 h reperfusion; (4) 20-min cardiac arrest and 8 h reperfusion. Soluble proteins and proteins from ribosomes and synaptosomes were assayed by a dinitrophenylhydrazine method for carbonyl groups, which are characteristic products of protein peroxidation. The ribosomal RNA was also examined by electrophoresis. When proteins from each fraction were peroxidized in vitro by Fenton reagents, carbonyl content increased as [Fe2+] was increased from 0 to 100 microM. However, following reperfusion there was no significant accumulation of carbonyl content in either the soluble (ANOVA P = 0.92) or ribosome (P = 0.10) protein fractions. There was a significant decrease in the carbonyl content of the synaptosome protein fraction after 8 h of reperfusion (P = 0.03). Similarly, although ribosomal RNA fragmentation was observed in ethidium stained agarose gels following in vitro reaction with Fenton reagents, there was no evidence of ribosomal RNA fragmentation or cross-linking following reperfusion. These results suggest that reperfusion free radical reactions do not involve these cellular proteins or ribosomal RNA.

Prevention of post-ischemic brain lipid conjugated diene production and neurological injury by hydroxyethyl starch-conjugated deferoxamine

Hydroxyethyl starch conjugated deferoxamine (DFO) was administered to rats following resuscitation from 6.5 min cardiac arrest (CA) in an attempt to prevent the iron-catalyzed production of oxygen free radicals which may lead to neurologic injury and ultimately death following restoration of spontaneous circulation (ROSC). Brain conjugated dienes were analyzed spectrophotometrically 4 and 24 hr following ROSC, and were found to be significantly elevated when compared to non-ischemic controls. Hydroxyethyl starch-DFO treated rats demonstrated no increased conjugated diene production at either period. Neurologic injury was significantly less in drug treated rats surviving 24 or 72 hours when compared to controls. While mortality was similar in drug treated or control rats for the first 24 hours following ROSC, delayed mortality (days 1-10) was significantly less in drug treated animals, presumably as a result of neurologic protection afforded by post-ischemic drug administration. Administration of DFO conjugated to hydroxyethyl starch appears to modulate the neurologic injury which occurs during brain ischemia and reperfusion.

Thymine glycols and pyrimidine dimers in brain DNA during post-ischemic reperfusion

Free-radical reactions, known to occur in the reperfused brain, damage DNA in vitro. We therefore examined the hypothesis that thymine glycols and thymine dimers, which are known to block transcription and are formed by free radical mechanisms, are formed in brain DNA during reoxygenation following ischemia. Such biochemical lesions could account for the failure of protein synthesis that occurs following an ischemic insult. Large dogs were anesthetized, instrumented, and divided into four groups: (1) non-ischemic controls; (2) 20-min cardiac arrest without resuscitation; (3) 20-min cardiac arrest, resuscitation and 2 h reperfusion; and (4) 20-min cardiac arrest, resuscitation and 8 h reperfusion. Genomic DNA was isolated from the cerebral cortex. Thymine glycols were labeled by reduction with [3H]NaBH4. Pyrimidine dimers were determined by ELISA using antibody prepared against ultraviolet irradiated DNA. The data was evaluated by Kruskal-Wallis ANOVA with alpha = 0.05. The rabbit antibodies detected the thymine dimer content in 10 pg UV irradiated DNA but did not react with normal DNA. Borohydride labeling qualitatively detected thymine glycols generated by treatment of DNA with osmium tetroxide. There was no difference between the DNAs from the experimental groups in the content of thymine glycols or pyrimidine dimers (P = 0.608 and P = 0.219, respectively). We conclude that significant quantities of thymine glycols and thymine dimers are not formed in brain DNA during post-ischemic reperfusion. Therefore, the inhibition of brain protein synthesis during reperfusion, observed by other investigators, is unlikely to be caused by interruption of transcription by these species.

Brain nuclear DNA survives cardiac arrest and reperfusion

Iron-mediated peroxidation of brain lipids is known to occur during reperfusion following cardiac arrest. Since in vitro damage to DNA is caused by similar iron-dependent peroxidation, we tested whether free radical damage to genomic DNA also develops during reperfusion following cardiac arrest and resuscitation. Genomic DNA was isolated from the cerebral cortex in (i) normal dogs, (ii) dogs subjected to a 20-min cardiac arrest, and (iii) dogs resuscitated from a 20-min cardiac arrest and then allowed to reperfuse for 2 or 8 h. DNA strand nicks were evaluated by in vitro labeling of newly created 3' and 5' termini. DNA base damage was evaluated utilizing reaction with piperidine prior to labeling of 5' termini. The 3' DNA termini were labeled before and after digestion with exonuclease III, and the 5' DNA termini were labeled before and after treatment with piperidine. In vitro experiments with genomic DNA damaged by oxygen radicals verified that these labeling methods identified radical damage. In the experimental animal groups, terminal incorporation and electrophoretic mobility of brain nuclear DNA are not significantly changed either by 20 min of complete brain ischemia or during the first 8 h of reperfusion. We conclude that genomic DNA is not extensively damaged during cardiac arrest and early reperfusion, and therefore such DNA damage does not appear to be an important early aspect of the neurologic injury that accompanies cardiac arrest and resuscitation.

Brain resuscitation

Optimal neurological outcome after cardiac arrest requires careful attention to the details of both intracranial and extracranial homeostasis. A high index of suspicion regarding the potential causes and complications of cardiac arrest facilitates discovery and treatment of problems before they adversely impact upon neurological outcome. The future is bright for resuscitation research since our fundamental understanding of cerebral ischemia and its consequences has dramatically improved. This knowledge can hopefully be transferred to clinical useful modes of therapy.