Neurological consequences of cardiac arrest: where do we stand?

Cardiac arrest and disorders of consciousness

As the second most common cause of coma and disorders of consciousness, cardiac arrest is defined as a cessation of cardiac mechanical activity and absence of circulation. Cardiac arrest can happen due to an intrinsic cardiac condition or secondary to noncardiac causes such as respiratory, neurologic, metabolic causes or external causes such as toxic ingestion, asphyxia, drowning, trauma, and other environmental exposures. While cardiac arrest resuscitation research and practice has evolved over decades, the overall survival to hospital discharge remains low across different types of cardiac arrest (about 9%-29%). This chapter focuses on disorders of consciousness after cardiac arrest and how it is different from other etiologies. It also discusses advances and controversies in diagnosis, management, prognostication and research.

Blood-Brain Barrier Rescue by Roflumilast After Transient Global Cerebral Ischemia in Rats

Phosphodiesterase 4 inhibitors (PDE4-I), which selectively increase cyclic adenosine monophosphate (cAMP) levels, have shown neuroprotective effects after several neurological injuries inducing blood-brain barrier (BBB) damage including local/focal cerebral ischemia. The present investigated whether roflumilast confers BBB neuroprotection in the hippocampus after transient global cerebral ischemia (TGCI) in rats. TGCI resulted in whole BBB disruption as measured by the increase of Evans blue (EB) and IgG extravasation, neurodegeneration, and downregulation of claudin-5 and endothelial nitric oxide synthase (eNOS) levels in the CA1 hippocampal subfield of ischemic rats. Roflumilast attenuated BBB disruption and restored the levels of eNOS in the CA1 hippocampal area. Moreover, roflumilast increased the levels of B2 cell lymphoma (BcL-2) and neuron-glial antigen-2 (NG2) in the CA1 subfield after global ischemia in rats. The protective effects of roflumilast against TGCI-induced BBB breakdown might involve preservation of BBB integrity, vascularization and angiogenesis, and myelin repair.

Microglial Activation and Neurological Outcomes in a Murine Model of Cardiac Arrest

BACKGROUND

Neurological injury following successful resuscitation from sudden cardiac arrest (CA) is common. The pathophysiological basis of this injury remains poorly understood, and treatment options are limited. Microglial activation and neuroinflammation are established contributors to many neuropathologies, such as Alzheimer disease and traumatic brain injury, but their potential role in post-CA injury has only recently been recognized. Here, we hypothesize that microglial activation that occurs following brief asystolic CA is associated with neurological injury and represents a potential therapeutic target.

METHODS

Adult C57BL/6 male and female mice were randomly assigned to 12-min, KCl-induced asystolic CA, under anesthesia and ventilation, followed by successful cardiopulmonary resuscitation (n = 19) or sham intervention (n = 11). Neurological assessments of mice were performed using standardized neurological scoring, video motion tracking, and sensory/motor testing. Mice were killed at 72 h for histological studies; neuronal degeneration was assessed using Fluoro-Jade C staining. Microglial characteristics were assessed by immunohistochemistry using the marker of ionized calcium binding adaptor molecule 1, followed by ImageJ analyses for cell integrity density and skeletal analyses.

RESULTS

Neurological injury in post-cardiopulmonary-resuscitation mice vs. sham mice was evident by poorer neurological scores (difference of 3.626 ± 0.4921, 95% confidence interval 2.618-4.634), sensory and motor functions (worsened by sixfold and sevenfold, respectively, compared with baseline), and locomotion (75% slower with a 76% decrease in total distance traveled). Post-CA brains demonstrated evidence of neurodegeneration and neuroinflammatory microglial activation.

CONCLUSIONS

Extensive microglial activation and neurodegeneration in the CA1 region and the dentate gyrus of the hippocampus are evident following brief asystolic CA and are associated with severe neurological injury.

The 5-HT1A receptor as a serotonergic target for neuroprotection in cerebral ischemia

Cerebral ischemia due to stroke or cardiac arrest greatly affects daily functioning and the quality of life of patients and has a high socioeconomic impact due to the surge in their prevalence. Advances in the identification of an effective pharmacotherapy to promote neuroprotection and recovery after a cerebral ischemic insult are, however, limited. The serotonin 1A (5-HT_1A) receptor has been implicated in the regulation of several brain functions, including mood, emotions, memory, and neuroplasticity, all of which are deleteriously affected by cerebral ischemia. This review focuses on the specific roles and mechanisms of 5-HT_1A receptors in neuroprotection in experimental models of cerebral ischemia. We present experimental evidence that 5-HT_1A receptor agonists can prevent neuronal damage and promote functional recovery induced by focal and transient global ischemia in rodents. However, indiscriminate activation of pre-and postsynaptic by non-biased 5-HT_1A receptor agonists may be a limiting factor in the anti-ischemic clinical efficacy of these compounds since 5-HT_1A receptors in different brain regions can mediate diverging or even contradictory responses. Current insights are presented into the 'biased' 5-HT_1A post-synaptic heteroreceptor agonist NLX-101 (also known as F15599), a compound that preferentially and potently stimulates postsynaptic cortical pyramidal neurons without inhibiting firing of serotoninergic neurons, as a potential strategy providing neuroprotection in cerebral ischemic conditions.

Neuroprotective Treatment of Postanoxic Encephalopathy: A Review of Clinical Evidence

Postanoxic encephalopathy is the key determinant of death or disability after successful cardiopulmonary resuscitation. Animal studies have provided proof-of-principle evidence of efficacy of divergent classes of neuroprotective treatments to promote brain recovery. However, apart from targeted temperature management (TTM), neuroprotective treatments are not included in current care of patients with postanoxic encephalopathy after cardiac arrest. We aimed to review the clinical evidence of efficacy of neuroprotective strategies to improve recovery of comatose patients after cardiac arrest and to propose future directions. We performed a systematic search of the literature to identify prospective, comparative clinical trials on interventions to improve neurological outcome of comatose patients after cardiac arrest. We included 53 studies on 21 interventions. None showed unequivocal benefit. TTM at 33 or 36°C and adrenaline (epinephrine) are studied most, followed by xenon, erythropoietin, and calcium antagonists. Lack of efficacy is associated with heterogeneity of patient groups and limited specificity of outcome measures. Ongoing and future trials will benefit from systematic collection of measures of baseline encephalopathy and sufficiently powered predefined subgroup analyses. Outcome measurement should include comprehensive neuropsychological follow-up, to show treatment effects that are not detectable by gross measures of functional recovery. To enhance translation from animal models to patients, studies under experimental conditions should adhere to strict methodological and publication guidelines.

Targeted Temperature Management With Total Liquid Ventilation After Ischemic Spinal Cord Injury

BACKGROUND

Ischemic spinal cord injury is a devastating condition after aortic surgery. We determined whether ultrafast and short whole-body hypothermia provided by total liquid ventilation (TLV) attenuated lower limb paralysis after aortic cross-clamping with a targeted temperature management at 33°C versus 36°C.

METHODS

Anesthetized rabbits were submitted to infrarenal aortic cross-clamping during 15 min. A control group (n = 7) was maintained at normothermia (38°C to 38.5°C) with conventional mechanical ventilation. In TLV groups, TLV was started after reperfusion and maintained during 30 min with a target temperature at either 33°C or 36°C (TLV-33°C and TLV-36°C, respectively; n = 7 in each condition). After TLV, animals were resumed to conventional ventilation. Hypothermia was maintained during 120 min, before rewarming and awakening. Hind limb motor function was assessed with modified Tarlov score at day 2 and infarct size in the spinal cord was determined using triphenyltetrazolium chloride staining.

RESULTS

Target temperature was achieved within 20 minutes in the two TLV groups. At day 2, the modified Tarlov score was significantly lower in the control group, as compared with TLV-33°C and TLV-36°C groups (0.0 ± 0.0 versus 3.1 ± 0.7 and 2.6 ± 0.6, respectively). The infarct size of the spinal cord was also significantly higher in the control group compared with TLV-33°C and TLV-36°C groups (75% ± 10% versus 32% ± 7% and 28% ± 10%, respectively). Neither motor function nor infarct size differed significantly between TLV-33°C and TLV-36°C groups.

CONCLUSIONS

Ultrafast hypothermic TLV attenuates spinal cord injury when applied after ischemic insult. Neurological outcome was similar with targeted temperature management at either 33°C or 36°C.

Prognostication in Anoxic Brain Injury

Cardiac arrest is a common cause of coma with frequent poor outcomes. Palliative medicine teams are often called upon to discuss the scope of treatment and future care in cases of anoxic brain injury. Understanding prognostic tools in this setting would help medical teams communicate more effectively with patients’ families and caregivers and may promote improved quality of life overall. This article reviews multiple tools that are useful in determining outcomes in the setting of postarrest anoxic brain injury.

Targeted temperature management using the "Esophageal Cooling Device" after cardiac arrest (the COOL study): A feasibility and safety study

BACKGROUND

Targeted temperature management (TTM) between 32 and 36°C is recommended after out-of-hospital cardiac arrest (OHCA). We aimed to assess the feasibility and safety of the "Esophageal Cooling Device" (ECD) in performing TTM.

PATIENTS AND METHODS

This single-centre, prospective, interventional study included 17 comatose OHCA patients. Main exclusion criteria were: delay between OHCA and return of spontaneous circulation (ROSC)>60min, delay between sustained ROSC and inclusion >360min, known oesophageal disease. A TTM between 32 and 34°C was performed using the ECD (Advanced Cooling Therapy, USA) connected to a heat exchanger console (Meditherm III^®, Gaymar, France), without cold fluids' use. Primary endpoint was feasibility of inducing, maintaining TTM, and rewarming using the ECD alone. Secondary endpoints were adverse events, focusing on potential digestive damages. Results were expressed as median (interquartiles 25-75).

RESULTS

Cooling rate to reach the Target Temperature (33°C-TT) was 0.26°C/h [0.19-0.36]. All patients reached the 32-34°C range with a time spent within the range of 26h [21-28] (3 patients did not reach 33°C). Temperature deviation outside the TT during TTM-maintenance was 0.10°C [0.03-0.20]. Time with deviation >1°C was 0h. Rewarming rate was 0.20°C/h [0.18-0.22]. Among the 16 gastrointestinal endoscopy procedures performed, 10 (62.5%) were normal. Minor oeso-gastric injuries (37.5% and 19%, respectively) were similar to usual orogastric tube injuries. One patient experienced severe oesophagitis mimicking peptic lesions, not cooling-related. No patient among the 9 alive at 3-month follow-up had gastrointestinal complains.

CONCLUSION

ECD seems an interesting, safe, accurate, semi-invasive cooling method in OHCA patients treated with 33°C-TTM, particularly during the maintenance phase.

Cannabidiol reduces neuroinflammation and promotes neuroplasticity and functional recovery after brain ischemia

This study investigated the effects of cannabidiol (CBD), a non-psychotomimetic phytochemical present in Cannabis sativa, on the cognitive and emotional impairments induced by bilateral common carotid artery occlusion (BCCAO) in mice. Using a multi-tiered behavioral testing battery during 21days, we found that BCCAO mice exhibited long-lasting functional deficits reflected by increase in anxiety-like behavior (day 9), memory impairments (days 12-18) and despair-like behavior (day 21). Short-term CBD 10mg/kg treatment prevented the cognitive and emotional impairments, attenuated hippocampal neurodegeneration and white matter (WM) injury, and reduced glial response that were induced by BCCAO. In addition, ischemic mice treated with CBD exhibited an increase in the hippocampal brain derived neurotrophic factor (BDNF) protein levels. CBD also stimulated neurogenesis and promoted dendritic restructuring in the hippocampus of BCCAO animals. Collectively, the present results demonstrate that short-term CBD treatment results in global functional recovery in ischemic mice and impacts multiple and distinct targets involved in the pathophysiology of brain ischemic injury.

Minimal EEG montage with high yield for the detection of status epilepticus in the setting of postanoxic brain damage

For the diagnosis of electrographic seizures or status epilepticus, we reduced the number of EEG-electrodes to make urgent EEG monitoring more feasible. Unlike the current existing research, with mixed results, we studied a specific population with postanoxic brain damage, expecting a higher yield of detection of ictal EEG patterns. In a population treated with therapeutic hypothermia post-cardiac arrest, the initial EEGs were reformatted in a longitudinal, a hairline and an 8-lead montage, and independently reviewed by two investigators. The EEGs were categorized into three categories: one without ictal EEG activity, one with interictal activity and one with probable electrographic seizure(s). Generalized ictal EEG activity was the most frequently observed EEG pattern. The average sensitivity for the detection of probable electrographic seizure(s) was 100 % for the 8-lead montage and 92 % in the hairline montage. In comparison to the routine longitudinal montage, the 8-lead montage proved to be reliable for the detection of electrographic seizure activity in a postanoxic population even with limited training in EEG interpretation. The hairline montage did not suffice with regard to the differential diagnosis of triphasic waves associated with metabolic encephalopathy and generalized nonconvulsive status epilepticus, but nonetheless detected the vast majority of probable electrographic seizure(s). Our results support the use of EEG monitoring with fewer electrodes for the detection of ictal EEG activity in the postanoxic population.

Time trends in organ donation after neurologic determination of death: a cohort study

BACKGROUND

The cause of brain injury may influence the number of organs that can be procured and transplanted with donation following neurologic determination of death. We investigated whether the distribution of causes responsible for neurologic death has changed over time and, if so, whether this has had an impact on organ quality, transplantation rates and recipient outcomes.

METHODS

We performed a cohort study involving consecutive brain-dead organ donors in southern Alberta between 2003 and 2014. For each donor, we determined last available measures of organ injury and number of organs transplanted, and compared these variables for various causes of neurologic death. We compared trends to national Canadian data for 2000-2013 (2000-2011 for Quebec).

RESULTS

There were 226 brain-dead organ donors over the study period, of whom 100 (44.2%) had anoxic brain injury, 63 (27.9%) had stroke, and 51 (22.6%) had traumatic brain injury. The relative proportion of donors with traumatic brain injury decreased over time (> 30% in 2003-2005 v. 6%-23% in 2012-2014) (p = 0.004), whereas that with anoxic brain injury increased (14%-37% v. 46%-80%, respectively) (p < 0.001). Nationally, the annual number of brain-dead donors with traumatic brain injury decreased from 4.4 to less than 3 per million population between 2000 and 2013, and that with anoxic brain injury increased from 1.1 to 3.1 per million. Donors with anoxic brain injury had higher concentrations of creatinine, alanine aminotransferase and troponin T, and lower PaO2/FIO2 and urine output than donors with other diagnoses. The average number of organs transplanted per donor was 3.6 with anoxic brain injury versus 4.5 with traumatic brain injury or stroke (p = 0.002).

INTERPRETATION

Anoxic brain injury has become a leading cause of organ donation after neurologic determination of death in Canada. Organs from donors with anoxic brain injury have a greater degree of injury, and fewer are transplanted. These findings have implications for availability of organs for transplantation in patients with end-stage organ failure.

Pretreated quercetin protects gerbil hippocampal CA1 pyramidal neurons from transient cerebral ischemic injury by increasing the expression of antioxidant enzymes

Quercetin (QE; 3,5,7,3′,4′-pentahydroxyflavone), a well-known flavonoid, has been shown to prevent against neurodegenerative disorders and ischemic insults. However, few studies are reported regarding the neuroprotective mechanisms of QE after ischemic insults. Therefore, in this study, we investigated the effects of QE on ischemic injury and the expression of antioxidant enzymes in the hippocampal CA1 region of gerbils subjected to 5 minutes of transient cerebral ischemia. QE was pre-treated once daily for 15 days before ischemia. Pretreatment with QE protected hippocampal CA1 pyramidal neurons from ischemic injury, which was confirmed by neuronal nuclear antigen immunohistochemistry and Fluoro-Jade B histofluorescence staining. In addition, pretreatment with QE significantly increased the expression levels of endogenous antioxidant enzymes Cu/Zn superoxide dismutase, Mn superoxide dismutase, catalase and glutathione peroxidase in the hippocampal CA1 pyramidal neurons of animals with ischemic injury. These findings demonstrate that pretreated QE displayed strong neuroprotective effects against transient cerebral ischemia by increasing the expression of antioxidant enzymes.

The phosphodiesterase type 2 inhibitor BAY 60-7550 reverses functional impairments induced by brain ischemia by decreasing hippocampal neurodegeneration and enhancing hippocampal neuronal plasticity

Cognitive and affective impairments are the most characterized consequences following cerebral ischemia. BAY 60-7550, a selective phosphodiesterase type 2 inhibitor (PDE2-I), presents memory-enhancing and anxiolytic-like properties. The behavioral effects of BAY 60-7550 have been associated with its ability to prevent hydrolysis of both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) thereby interfering with neuronal plasticity. Here, we hypothesize that PDE2-I treatment could promote functional recovery after brain ischemia. Mice C57Bl/6 were submitted to bilateral common carotid artery occlusion (BCCAO), an experimental model of transient brain ischemia, for 20 min. During 21 days after reperfusion, the animals were tested in a battery of behavioral tests including the elevated zero maze (EZM), object location task (OLT) and forced swim test (FST). The effects of BAY 60-7550 were evaluated on neuronal nuclei (NeuN), caspase-9, cAMP response element-binding protein (CREB), phosphorylated CREB (pCREB) and brain-derived neurotrophic factor (BDNF) expression in the hippocampus. BCCAO increased anxiety levels, impaired hippocampus-dependent cognitive function and induced despair-like behavior in mice. Hippocampal neurodegeneration was evidenced by a decrease in NeuN and increase incaspase-9 protein levels in BCCAO mice. Ischemic mice also showed low BDNF protein levels in the hippocampus. Repeated treatment with BAY 60-7550 attenuated the behavioral impairments induced by BCCAO in mice. Concomitantly, BAY 60-7550 enhanced expression of pCREB and BDNF protein levels in the hippocampus of ischemic mice. The present findings suggest that chronic inhibition of PDE2 provides functional recovery in BCCAO mice possibly by augmenting hippocampal neuronal plasticity.