Treatment with the competitive NMDA antagonist GPI 3000 does not improve outcome after cardiac arrest in dogs

The influences of morphine or ketamine pre-treatment on hemodynamic, acid-base status, biochemical markers of brain damage and early survival in rats after asphyxial cardiac arrest

BACKGROUND

In different models of hypoxia, blockade of opioid or N-methyl-D-aspartate (NMDA) receptors shows cardio- and neuroprotective effects with a consequent increase in animal survival. The aim of the study was to investigate effects of pre-treatment with Morphine or Ketamine on hemodynamic, acid-base status, early survival, and biochemical markers of brain damage in a rat model of asphyxial cardiac arrest (ACA).

METHODS

Under anaesthesia with Thiopental Sodium 60 mg/kg, i.p., Wistar rats (n = 42) were tracheostomized and catheters were inserted in a femoral vein and artery. After randomization, the rats were pre-treated with: Morphine 5 mg/kg i.v. (n = 14); Ketamine 40 mg/kg i.v. (n = 14); or equal volume of i.v. NaCl 0.9% as a Control (n = 14). ACA was induced by corking of the tracheal tube for 8 min, and defined as a mean arterial pressure (MAP) < 20 mmHg. Resuscitation was started at 5 min after cardiac arrest (CA). Invasive MAP was recorded during experiments. Arterial pH and blood gases were sampled at baseline (BL) and 10 min after CA. At the end of experiments, all surviving rats were euthanised, brain and blood samples for measurement of Neuron Specific Enolase (NSE), s100 calcium binding protein B (s100B) and Caspase-3 (CS-3) were retrieved.

RESULTS

At BL no differences between groups were found in hemodynamic or acid-base status. After 3 min of asphyxia, all animals had cardiac arrest (CA). Return of spontaneous circulation (MAP > 60 mmHg) was achieved in all animals within 3 min after CA. At the end of the experiment, the Ketamine pre-treated group had increased survival (13 of 14; 93%) compared to the Control (7 of 14; 50%) and Morphine (10 of 14; 72%) groups (p = 0.035). Biochemical analysis of plasma concentration of NSE and s100B as well as an analysis of CS-3 levels in the brain tissue did not reveal any differences between the study groups.

CONCLUSION

In rats after ACA, pre-treatment with Morphine or Ketamine did not have any significant influence on hemodynamic and biochemical markers of brain damage. However, significantly better pH level and increased early survival were found in the Ketamine pre-treated group.

Xenon: An Emerging Neuroprotectant With Potential Application for Cardiac Arrest Care

Xenon is an inert, highly polarizable noble gas with demonstrated safety and application in general anesthesia for over 50 years. A potent inhibitor of the N-methyl-D-aspartate subtype of glutamate receptors, xenon has a well-documented ameliorating effect on excitotoxic neuronal injury in numerous cellular and animal models of hypoxic-ischemic brain injury. The most important determinant of overall survival and morbidity in out-of-hospital cardiac arrest is the severity of neurological injury. The only approved neuroprotective strategy in this setting is mild therapeutic hypothermia, which has demonstrated significant, albeit modest, improvements in mortality. The combination therapy of therapeutic hypothermia and xenon in porcine models of cardiac arrest has shown a greater improvement in functional outcomes than either intervention alone, thereby prompting the study of combination therapy in randomized clinical trials. The treatment of postarrest patients with xenon and mild hypothermia is safe and demonstrates favorable cardiovascular features, including a reduced heart rate, a reduction in troponin elevations, and a decreased need for vasopressors. Combination therapy is superior in protecting white matter integrity than hypothermia alone, but did not significantly impact neurological outcomes at 6-month follow-up. Despite an abundance of preclinical evidence supporting xenon's neuroprotective properties, its translational potential in postcardiac arrest care is indeterminate due to a lack of adequately-powered studies.

A systematic review of neuroprotective strategies after cardiac arrest: from bench to bedside (Part I - Protection via specific pathways)

Neurocognitive deficits are a major source of morbidity in survivors of cardiac arrest. Treatment options that could be implemented either during cardiopulmonary resuscitation or after return of spontaneous circulation to improve these neurological deficits are limited. We conducted a literature review of treatment protocols designed to evaluate neurologic outcome and survival following cardiac arrest with associated global cerebral ischemia. The search was limited to investigational therapies that were utilized to treat global cerebral ischemia associated with cardiac arrest. In this review we discuss potential mechanisms of neurologic protection following cardiac arrest including actions of several medical gases such as xenon, argon, and nitric oxide. The 3 included mechanisms are: 1. Modulation of neuronal cell death; 2. Alteration of oxygen free radicals; and 3. Improving cerebral hemodynamics. Only a few approaches have been evaluated in limited fashion in cardiac arrest patients and results show inconclusive neuroprotective effects. Future research focusing on combined neuroprotective strategies that target multiple pathways are compelling in the setting of global brain ischemia resulting from cardiac arrest.

Amiloride but not memantine reduces neurodegeneration, seizures and myoclonic jerks in rats with cardiac arrest-induced global cerebral hypoxia and reperfusion

It has been reported that both activation of N-methyl-D-aspartate receptors and acid-sensing ion channels during cerebral ischemic insult contributed to brain injury. But which of these two molecular targets plays a more pivotal role in hypoxia-induced brain injury during ischemia is not known. In this study, the neuroprotective effects of an acid-sensing cation channel blocker and an N-methyl-D-aspartate receptor blocker were evaluated in a rat model of cardiac arrest-induced cerebral hypoxia. We found that intracisternal injection of amiloride, an acid-sensing ion channel blocker, dose-dependently reduced cerebral hypoxia-induced neurodegeneration, seizures, and audiogenic myoclonic jerks. In contrast, intracisternal injection of memantine, a selective uncompetitive N-methyl-D-aspartate receptor blocker, had no significant effect on cerebral hypoxia-induced neurodegeneration, seizure and audiogenic myoclonic jerks. Intracisternal injection of zoniporide, a specific sodium-hydrogen exchanger inhibitor, before cardiac arrest-induced cerebral hypoxia, also did not reduce cerebral hypoxia-induced neurodegeneration, seizures and myoclonic jerks. These results suggest that acid-sensing ion channels play a more pivotal role than N-methyl-D-aspartate receptors in mediating cerebral hypoxia-induced brain injury during ischemic insult.

Mild hypothermia attenuates mitochondrial oxidative stress by protecting respiratory enzymes and upregulating MnSOD in a pig model of cardiac arrest

Mild hypothermia is the only effective treatment confirmed clinically to improve neurological outcomes for comatose patients with cardiac arrest. However, the underlying mechanism is not fully elucidated. In this study, our aim was to determine the effect of mild hypothermia on mitochondrial oxidative stress in the cerebral cortex. We intravascularly induced mild hypothermia (33°C), maintained this temperature for 12 h, and actively rewarmed in the inbred Chinese Wuzhishan minipigs successfully resuscitated after 8 min of untreated ventricular fibrillation. Cerebral samples were collected at 24 and 72 h following return of spontaneous circulation (ROSC). We found that mitochondrial malondialdehyde and protein carbonyl levels were significantly increased in the cerebral cortex in normothermic pigs even at 24 h after ROSC, whereas mild hypothermia attenuated this increase. Moreover, mild hypothermia attenuated the decrease in Complex I and Complex III (i.e., major sites of reactive oxygen species production) activities of the mitochondrial respiratory chain and increased antioxidant enzyme manganese superoxide dismutase (MnSOD) activity. This increase in MnSOD activity was consistent with the upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA and protein expressions, and with the increase of Nrf2 nuclear translocation in normothermic pigs at 24 and 72 h following ROSC, whereas mild hypothermia enhanced these tendencies. Thus, our findings indicate that mild hypothermia attenuates mitochondrial oxidative stress in the cerebral cortex, which may be associated with reduced impairment of mitochondrial respiratory chain enzymes, and enhancement of MnSOD activity and expression via Nrf2 activation.

The beneficial effect of mild therapeutic hypothermia depends on the time of complete circulatory standstill in patients with cardiac arrest

AIM

Mild therapeutic hypothermia has shown to improve long-time survival as well as favorable functional outcome after cardiac arrest. Animal models suggest that ischemic durations beyond 8 min results in progressively worse neurologic deficits. Based on these considerations, it would be obvious that cardiac arrest survivors would benefit most from mild therapeutic hypothermia if they have reached a complete circulatory standstill of more than 8 min.

METHODS

In this retrospective cohort study we included cardiac arrest survivors of 18 years of age or older suffering a witnessed out-of-hospital cardiac arrest, which remain comatose after restoration of spontaneous circulation. Data were collected from 1992 to 2010. We investigated the interaction of 'no-flow' time on the association between post arrest mild therapeutic hypothermia and good neurological outcome. 'No-flow' time was categorized into time quartiles (0, 1-2, 3-8, >8 min).

RESULTS

One thousand-two-hundred patients were analyzed. Hypothermia was induced in 598 patients. In spite of showing a statistically significant improvement in favorable neurologic outcome in all patients treated with mild therapeutic hypothermia (odds ratio [OR]: 1.49; 95% confidence interval [CI]: 1.14-1.93) this effect varies with 'no-flow' time. The effect is significant in patients with 'no-flow' times of more than 2 min (OR: 2.72; CI: 1.35-5.48) with the maximum benefit in those with 'no-flow' times beyond 8 min (OR: 6.15; CI: 2.23-16.99).

CONCLUSION

The beneficial effect of mild therapeutic hypothermia increases with cumulative time of complete circulatory standstill in patients with witnessed out-of-hospital cardiac arrest.

Mechanisms of action, physiological effects, and complications of hypothermia

BACKGROUND

Mild to moderate hypothermia (32-35 degrees C) is the first treatment with proven efficacy for postischemic neurological injury. In recent years important insights have been gained into the mechanisms underlying hypothermia's protective effects; in addition, physiological and pathophysiological changes associated with cooling have become better understood.

OBJECTIVE

To discuss hypothermia's mechanisms of action, to review (patho)physiological changes associated with cooling, and to discuss potential side effects.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

A myriad of destructive processes unfold in injured tissue following ischemia-reperfusion. These include excitotoxicty, neuroinflammation, apoptosis, free radical production, seizure activity, blood-brain barrier disruption, blood vessel leakage, cerebral thermopooling, and numerous others. The severity of this destructive cascade determines whether injured cells will survive or die. Hypothermia can inhibit or mitigate all of these mechanisms, while stimulating protective systems such as early gene activation. Hypothermia is also effective in mitigating intracranial hypertension and reducing brain edema. Side effects include immunosuppression with increased infection risk, cold diuresis and hypovolemia, electrolyte disorders, insulin resistance, impaired drug clearance, and mild coagulopathy. Targeted interventions are required to effectively manage these side effects. Hypothermia does not decrease myocardial contractility or induce hypotension if hypovolemia is corrected, and preliminary evidence suggests that it can be safely used in patients with cardiac shock. Cardiac output will decrease due to hypothermia-induced bradycardia, but given that metabolic rate also decreases the balance between supply and demand, is usually maintained or improved. In contrast to deep hypothermia (<or=30 degrees C), moderate hypothermia does not induce arrhythmias; indeed, the evidence suggests that arrhythmias can be prevented and/or more easily treated under hypothermic conditions.

CONCLUSIONS

Therapeutic hypothermia is a highly promising treatment, but the potential side effects need to be properly managed particularly if prolonged treatment periods are required. Understanding the underlying mechanisms, awareness of physiological changes associated with cooling, and prevention of potential side effects are all key factors for its effective clinical usage.

Future directions in the management of pain by intraspinal drug delivery

Management of pain by intraspinal delivery of drugs enables physicians to target specific sites of action. While this novel approach is gaining increasing use, well-designed studies are needed. A major limitation is the lack of published information on existing drugs used for intrathecal delivery. (The strengths and weaknesses of this information are reviewed in the accompanying literature review article.) Promising agents such as bupivacaine, hydromorphone, and morphine/clonidine combinations warrant further research in large prospective (ideally randomized and double-blind) clinical safety and efficacy studies. These studies may provide data for pain management guidelines, such as those included in the preceding paper. Research must also address issues of formulation, chemical stability/compatibility, pharmacokinetics, and toxicology during clinical development and drug approval. Finally, more basic studies and early phase trials of other potential agents for intrathecal pain management (e.g., gabapentin) are needed.

AR-R15896AR reduces cerebral infarction volumes after focal ischemia in cats

OBJECTIVE

The use of competitive and noncompetitive N-methyl-D-aspartate receptor antagonists to prevent neuronal death during ischemia has been comprehensively studied. This study was performed to examine the neuroprotective effects and pharmacokinetics of the noncompetitive N-methyl-D-aspartate receptor channel blocker (S)-alpha-phenylpyridine-ethanamine dihydrochloride, AR-R15896AR (formerly designated ARL 15896AR), using a gyrencephalic cat middle cerebral artery occlusion model.

METHODS

In a separate experiment, three cats were used for pharmacokinetic analysis, thus establishing the optimal dose of AR-R15896AR. Focal cerebral ischemia was induced in 21 cats. After 30 minutes of a 90-min ischemic insult, the cats received an intravenous infusion (total volume, 3 ml), in a 15-minute period, of either AR-R15896AR or normal saline solution (control). Physiological data were obtained after 40 and 80 minutes of ischemia and at 2, 4, and 6 hours after ischemia. At 6 hours after ischemia, each cat was positioned for both T2- and diffusion-weighted scans (eight slices, 5-mm thick). At 8 hours after ischemia, the animals were perfusion-fixed for histopathological analysis.

RESULTS

Pharmacokinetic studies indicated that AR-R15896AR remained in the blood at elevated levels for the 6 hours studied, with a calculated half-life of approximately 6 hours. AR-R15896AR rapidly entered the brain and exhibited a brain/plasma ratio of approximately 8:1. The infarction volumes for the AR-R15896AR-treated group were 1138.5+/-363.1, 651.3+/-428.9, and 118.6+/-50.1 mm3, as calculated using diffusion- and T2-weighted MRI and histopathological data, respectively. The infarction volumes for the control group were 3866.3+/-921, 3536+/-995.7, and 359.9+/-80.2 mm3, as calculated using diffusion- and T2-weighted MRI and histopathological data, respectively. No significant changes were observed in the physiological parameters measured (mean arterial blood pressure, pH, arterial carbon dioxide pressure, arterial oxygen pressure, sodium, potassium, chloride, and glucose levels, hematocrit, and temperature) for either the control or AR-R15896AR-treated group. Postischemic calcium levels returned to normal in the AR-R15896AR-treated cats, whereas they decreased in the control cats.

CONCLUSION

When administered after ischemia, AR-R15896AR was effective in significantly reducing infarction volumes, as measured using diffusion- or T2-weighted magnetic resonance imaging data or quantitative histopathological data. This study also demonstrated that infarction volumes were greater in the diffusion- and T2-weighted magnetic resonance imaging scans than in the qualitative histopathological analyses, with the diffusion-weighted scans exibiting the largest infarction volumes.