Improving neurological outcomes post-cardiac arrest in a rat model: immediate hypothermia and quantitative EEG monitoring

Multimodel quantitative analysis of somatosensory evoked potentials after cardiac arrest with graded hypothermia

Cardiac arrest (CA) is one of the most prominent causes of morbidity and mortality in adults. Therapeutic hypothermia (TH) is a recommended treatment to improve survival and functional outcome following CA, however, it is unclear what degree of TH is most beneficial. It has been suggested that TH of 33°C provides no survival or outcome benefits over TH of 36°C. Additionally, there is a lack of verified objective quantitative prognostic tools for comatose CA patients under TH. In this study, we calculated three quantitative markers of somatosensory evoked potentials (SSEP) to examine their potential to track recovery in the early period following CA under graded TH. A total of 16 rats were randomly divided among 4 temperature groups (n=4/group): normothermia (N0, 36.5-37.5°C), hypothermia 1 (H1, 30-32°C), hypothermia 2 (H2, 32-34°C) and hypothermia 3 (H3, 34-36°C). All rats underwent a 15min baseline SSEP recording followed by 9min asphyxial-CA, resulting in severe cerebral injury, and immediate temperature management following resuscitation for 6 hours. SSEP recordings were maintained in 15 min intervals from 30min-4hrs after resuscitation. The N10 amplitude, N10 latency and quantitative SSEP phase space area (qSSEP-PSA) were calculated for the early recovery period and normalized to their respective baselines. Functional recovery was determined by the neurological deficit scale (NDS). N10 amplitude was significantly larger in H1, H2 and H3 compared to N0. N10 latency was significantly longer in H1 than all temperature groups and all hypothermia groups had significantly longer latencies than N0. qSSEP-PSA had significantly better recovery in H1 and H2 than N0. Animals with good outcome (72hr NDS>50) had better recovery of all markers. N10 amplitude was significantly correlated with N10 latency and qSSEP-PSA. The results importantly demonstrate that quantified SSEPs have the potential to objectively track recovery following CA with graded TH.

Dihydrocapsaicin-induced hypothermia after asphyxiai cardiac arrest in rats

Cardiac arrest (CA) is one of the leading causes of mortality and morbidity in the world. Fast, reversible and controllable pharmaceutical-induced hypothermia (PIH) is strongly desired to treat ischemia-reperfusion brain injury. Dihydrocapsaicin (DHC), an agonist of transient receptor potential vanilloid type 1 cation channel (TRPV1), is an emerging candidate for PIH. Its capability to lower body temperature has been validated in both healthy and stroke animal models. However, DHC has shown cardiovascular effects and its safety and feasibility in a CA model has not been tested. Additionally, activated TRPV1 has multiple functions in addition to regulating body temperature and its effect on neurological recovery needs to be evaluated. In this study, we compared two methods of DHC administration, bolus injection and infusion via the femoral vein. We found that cardiovascular effects were only seen with a large dose DHC bolus injection. Then, we applied DHC-induced hypothermia in an asphyxial-CA rat model. We showed that DHC-treated rats were viable. Four-hour infusion of DHC at a rate of 0.75 mg/kg/h after CA maintained a body temperature of about 34 °C for at least 8 hours. DHC-treated rats had higher electrical activity during the first 4 hours after CA and had better neurological recovery during the 3 days after CA compared with normothermia rats. Additional pathway investigation of DHC administration following CA will further uncover the benefits of DHC-induced hypothermia.

Influence of argon on temperature modulation and neurological outcome in hypothermia treated rats following cardiac arrest

AIM OF THE STUDY

Combining xenon and mild therapeutic hypothermia (MTH) after cardiac arrest (CA) confers a degree of protection that is greater than either of the two interventions alone. However, xenon is very costly which might preclude a widespread use. We investigated whether the inexpensive gas argon would enhance hypothermia induced neurologic recovery in a similar manner.

METHODS

Following nine minutes of CA and three minutes of cardiopulmonary resuscitation 21 male Sprague-Dawley rats were randomized to receive MTH (33°C for 6h), MTH plus argon (70% for 1h), or no treatment. A first day condition score assessed behaviour, motor activity and overall condition. A neurological deficit score (NDS) was calculated daily for seven days following the experiment before the animals were killed and the brains harvested for histopathological analysis.

RESULTS

All animals survived. Animals that received MTH alone showed best overall neurologic function. Strikingly, this effect was abolished in the argon-augmented MTH group, where animals showed worse neurologic outcome being significant in the first day condition score and on day one to three and five in the NDS in comparison to MTH treated rats. Results were reflected by the neurohistopathological analysis.

CONCLUSION

Our study demonstrates that argon augmented MTH does not improve functional recovery after CA in rats, but may even worsen neurologic function in this model.

Practice guideline summary: Reducing brain injury following cardiopulmonary resuscitation: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology

OBJECTIVE

To assess the evidence and make evidence-based recommendations for acute interventions to reduce brain injury in adult patients who are comatose after successful cardiopulmonary resuscitation.

METHODS

Published literature from 1966 to August 29, 2016, was reviewed with evidence-based classification of relevant articles.

RESULTS AND RECOMMENDATIONS

For patients who are comatose in whom the initial cardiac rhythm is either pulseless ventricular tachycardia (VT) or ventricular fibrillation (VF) after out-of-hospital cardiac arrest (OHCA), therapeutic hypothermia (TH; 32-34°C for 24 hours) is highly likely to be effective in improving functional neurologic outcome and survival compared with non-TH and should be offered (Level A). For patients who are comatose in whom the initial cardiac rhythm is either VT/VF or asystole/pulseless electrical activity (PEA) after OHCA, targeted temperature management (36°C for 24 hours, followed by 8 hours of rewarming to 37°C, and temperature maintenance below 37.5°C until 72 hours) is likely as effective as TH and is an acceptable alternative (Level B). For patients who are comatose with an initial rhythm of PEA/asystole, TH possibly improves survival and functional neurologic outcome at discharge vs standard care and may be offered (Level C). Prehospital cooling as an adjunct to TH is highly likely to be ineffective in further improving neurologic outcome and survival and should not be offered (Level A). Other pharmacologic and nonpharmacologic strategies (applied with or without concomitant TH) are also reviewed.

Neuronal injury and tumor necrosis factor-alpha immunoreactivity in the rat hippocampus in the early period of asphyxia-induced cardiac arrest under normothermia

Low survival rate occurs in patients who initially experience a spontaneous return of circulation after cardiac arrest (CA). In this study, we induced asphyxial CA in adult male Sprague-Daley rats, maintained their body temperature at 37 ± 0.5°C, and then observed the survival rate during the post-resuscitation phase. We examined neuronal damage in the hippocampus using cresyl violet (CV) and Fluore-Jade B (F-J B) staining, and pro-inflammatory response using ionized calcium-binding adapter molecule 1 (Iba-1), glial fibrillary acidic protein (GFAP), and tumor necrosis factor-alpha (TNF-α) immunohistochemistry in the hippocampus after asphyxial CA in rats under normothermia. Our results show that the survival rate decreased gradually post-CA (about 63% at 6 hours, 37% at 1 day, and 8% at 2 days post-CA). Rats were sacrificed at these points in time post-CA, and no neuronal damage was found in the hippocampus until 1 day post-CA. However, some neurons in the stratum pyramidale of the CA region in the hippocampus were dead 2 days post-CA. Iba-1 immunoreactive microglia in the CA1 region did not change until 1 day post-CA, and they were activated (enlarged cell bodies with short and thicken processes) in all layers 2 days post-CA. Meanwhile, GFAP-immunoreactive astrocytes did not change significantly until 2 days post-CA. TNF-α immunoreactivity decreased significantly in neurons of the stratum pyramidale in the CA1 region 6 hours post-CA, decreased gradually until 1 day post-CA, and increased significantly again 2 days post-CA. These findings suggest that low survival rate of normothermic rats in the early period of asphyxia-induced CA is related to increased TNF-α immunoreactivity, but not to neuronal damage in the hippocampal CA1 region.

Brain Monitoring in Critically Neurologically Impaired Patients

Assessment of neurologic injury and the evolution of severe neurologic injury is limited in comatose or critically ill patients that lack a reliable neurologic examination. For common yet severe pathologies such as the comatose state after cardiac arrest, aneurysmal subarachnoid hemorrhage (aSAH), and severe traumatic brain injury (TBI), critical medical decisions are made on the basis of the neurologic injury. Decisions regarding active intensive care management, need for neurosurgical intervention, and withdrawal of care, depend on a reliable, high-quality assessment of the true state of neurologic injury, and have traditionally relied on limited assessments such as intracranial pressure monitoring and electroencephalogram. However, even within TBI there exists a spectrum of disease that is likely not captured by such limited monitoring and thus a more directed effort towards obtaining a more robust biophysical signature of the individual patient must be undertaken. In this review, multimodal monitoring including the most promising serum markers of neuronal injury, cerebral microdialysis, brain tissue oxygenation, and pressure reactivity index to access brain microenvironment will be discussed with their utility among specific pathologies that may help determine a more complete picture of the neurologic injury state for active intensive care management and long-term outcomes. Goal-directed therapy guided by a multi-modality approach appears to be superior to standard intracranial pressure (ICP) guided therapy and should be explored further across multiple pathologies. Future directions including the application of optogenetics to evaluate brain injury and recovery and even as an adjunct monitoring modality will also be discussed.

Efficacy of Selective Brain Cooling Using a Nasopharyngeal Method in Piglets

BACKGROUND

Mild hypothermia is an effective neuroprotective strategy for a variety of acute brain injuries. Cooling the nasopharynx may offer the capability to cool the brain selectively due to anatomic proximity of the internal carotid artery to the cavernous sinus. This study investigated the feasibility and efficiency of nasopharyngeal brain cooling by continuously blowing room temperature or cold air at different flow rates into the nostrils of normal newborn piglets.

METHODS

Experiments were conducted on thirty piglets (n = 30, weight = 2.7 ± 1.5 kg). Piglets were anesthetized with 1–2% isoflurane and were randomized to receive one of four different nasopharyngeal cooling treatments: I. Room temperature at a flow rate of 3–4 L min(−1) (n = 6); II. −1 ± 2 °C at a flow rate of 3–4 L min(−1) (n = 6); III. Room temperature at a flow rate of 14–15 L min(−1) (n = 6); IV. −8 ± 2 °C at a flow rate of 14–15 L min(−1) (n = 6). To control for the normal thermal regulatory response of piglets without nasopharyngeal cooling, a control group of piglets (n = 6) had their brain temperature monitored without nasopharyngeal cooling. The duration of treatment was 60 min, with additional 30 min of observation.

RESULTS

In group I, median cooling rate was 1.7 ± 0.9 °C/h by setting the flow rate of room temperature air to 3–4 L min(−1). Results of comparing different temperatures and flow rates in the nasopharyngeal cooling approach reveal that the brain temperature could be reduced rapidly at a rate of 5.5 ± 1.1 °C/h by blowing −8 ± 2 °C air at a flow rate of 14–15 L min(−1).

CONCLUSIONS

Nasopharyngeal cooling via cooled insufflated air can lower the brain temperature, with higher flows and lower temperatures of insufflated air being more effective.

Cerebral blood flow is decoupled from blood pressure and linked to EEG bursting after resuscitation from cardiac arrest

In the present study, we have developed a multi-modal instrument that combines laser speckle imaging, arterial blood pressure, and electroencephalography (EEG) to quantitatively assess cerebral blood flow (CBF), mean arterial pressure (MAP), and brain electrophysiology before, during, and after asphyxial cardiac arrest (CA) and resuscitation. Using the acquired data, we quantified the time and magnitude of the CBF hyperemic peak and stabilized hypoperfusion after resuscitation. Furthermore, we assessed the correlation between CBF and MAP before and after stabilized hypoperfusion. Finally, we examined when brain electrical activity resumes after resuscitation from CA with relation to CBF and MAP, and developed an empirical predictive model to predict when brain electrical activity resumes after resuscitation from CA. Our results show that: 1) more severe CA results in longer time to stabilized cerebral hypoperfusion; 2) CBF and MAP are coupled before stabilized hypoperfusion and uncoupled after stabilized hypoperfusion; 3) EEG activity (bursting) resumes after the CBF hyperemic phase and before stabilized hypoperfusion; 4) CBF predicts when EEG activity resumes for 5-min asphyxial CA, but is a poor predictor for 7-min asphyxial CA. Together, these novel findings highlight the importance of using multi-modal approaches to investigate CA recovery to better understand physiological processes and ultimately improve neurological outcome.

Real-time monitoring of cerebral blood flow by laser speckle contrast imaging after cardiac arrest in rat

Cardiac arrest (CA) results in global brain ischemia. To explore the role of cerebral blood flow (CBF) during ischemia, laser speckle contrast imaging (LSCI), a full-field high-resolution optical imaging technique, was used for real-time monitoring of the fluctuations of CBF in a rat model of asphyxial-CA. The temporal changes of CBF were characterized and the relationship between CBF and mean arterial pressure (MAP) was evaluated. Asphyxial-CA led to transient CBF dysregulation, manifested by changes in CBF velocity were significantly impacted by MAP. Hyperemia is aligned with a bolus injection of vecuronium, the first two minutes of asphyxia, the time of epinephrine injection and cardiopulmonary resuscitation, and then lasted for 13 min after the return of spontaneous respiratory (ROSC), followed by hypoperfusion about 55-70% of baseline level no later than 40 min after ROSC. Interestingly, we found that the velocity of venule blood flow increased more than that of the arteriole blood flow during the hyperemia (176% vs 120%). Our study, for the first time, shows real-time CBF changes during and immediately after asphyxial-CA, with high spatial and temporal resolution images. The quantified cerebro-vascular response during the different phases of recovery after CA may underlie the mechanism of injury and recovery after brain ischemia. The study provides a new technique to study the neurovascular coupling and metabolic regulation of CBF after CA.

Glibenclamide Is Comparable to Target Temperature Management in Improving Survival and Neurological Outcome After Asphyxial Cardiac Arrest in Rats

Background

We previously have shown that glibenclamide (GBC), a sulfonylurea receptor 1–transient receptor potential M4 (SUR1‐TRPM4) channel inhibitor, improves survival and neurological outcome after asphyxial cardiac arrest and cardiopulmonary resuscitation (ACA/CPR). Here, we further compare the efficacy of GBC with target temperature management (TTM) and determine whether the efficacy of GBC is affected by TTM.

Methods and Results

Male Sprague‐Dawley rats (n=213) subjected to 10‐minute ACA/CPR were randomized to 4 groups after return of spontaneous circulation (ROSC): normothermia control (NT); GBC; TTM; and TTM+GBC. Survival, neurodeficit scores, histological injury, as well as the expressions of SUR1 and TRPM4 were evaluated. The 7‐day survival rate was 34.4% (11 of 32) in the NT group, 65% (13 of 20) in the GBC group, 50% (10 of 20) in the TTM group, and 70% (14 of 20) in the TTM+GBC group. Rats that received either GBC, TTM alone, or in combination showed less neurological deficit than NT control at 24, 48, and 72 hours and 7 days after ROSC. Moreover, TTM or GBC ameliorated neuronal degeneration and glial activation in the hippocampal CA1 region with similar efficacy, whereas the combination of them had a trend toward better effect. The subunits of SUR1‐TRPM4 heterodimers were both strongly upregulated after ACA/CPR and expressed in multiple types of brain cells, but partly suppressed by TTM.

Conclusions

GBC is comparable to TTM in improving survival and neurological outcome after ACA/CPR. When GBC is given along with TTM, less histological injury tended to be achieved.

Edaravone improves survival and neurological outcomes after CPR in a ventricular fibrillation model of rats

OBJECTIVE

Overproduction of free radicals is a main factor contributing to cerebral injury after cardiac arrest (CA)/cardiopulmonary resuscitation (CPR). We sought to evaluate the impact of edaravone on the survival and neurological outcomes after CA/CPR in rats.

METHODS

Rats were subjected to CA following CPR. For survival study, the rats with restoration of spontaneous circulation (ROSC) were randomly allocated to one of the two groups (edaravone and saline group, n=20/each group) to received Edaravone (3 mg/kg) or normal saline. Another 10 rats without experiencing CA and CPR served as the sham group. Survival was observed for 72 hours and the neurological deficit score (NDS) was calculated at 12, 24, 48, and 72 hours after ROSC. For the neurological biochemical analysis study, rats were subjected to the same experimental procedures. Then, edaravone group (n=24), saline group (n=24) and sham group (n=16) were further divided into 4 subgroups according to the different time intervals (12, 24, 48, and 72 hours following ROSC). Brain tissues were harvested at relative time intervals for evaluation of oxidative stress, TUNEL staining and apoptotic gene expression.

RESULTS

Edaravone improved postresuscitative survival time and neurological deficit, decreased brain malonylaldehyde level, increased superoxide dismutase activities, decreased proapoptotic gene expression of capase-8, capase-3, and Bax, and increased antiapoptotic Bcl-2 expression at 12, 24, 48, and 72 hours after ROSC.

CONCLUSIONS

Edaravone improves survival and neurological outcomes following CPR via antioxidative and antiapoptotic effects in rats.

Cardiac arrest triggers hippocampal neuronal death through autophagic and apoptotic pathways

The mechanism of neuronal death induced by ischemic injury remains unknown. We investigated whether autophagy and p53 signaling played a role in the apoptosis of hippocampal neurons following global cerebral ischemia-reperfusion (I/R) injury, in a rat model of 8-min asphyxial cardiac arrest (CA) and resuscitation. Increased autophagosome numbers, expression of lysosomal cathepsin B, cathepsin D, Beclin-1, and microtubule-associated protein light chain 3 (LC3) suggested autophagy in hippocampal cells. The expression of tumor suppressor protein 53 (p53) and its target genes: Bax, p53-upregulated modulator of apoptosis (PUMA), and damage-regulated autophagy modulator (DRAM) were upregulated following CA. The p53-specific inhibitor pifithrin-α (PFT-α) significantly reduced the expression of pro-apoptotic proteins (Bax and PUMA) and autophagic proteins (LC3-II and DRAM) that generally increase following CA. PFT-α also reduced hippocampal neuronal damage following CA. Similarly, 3-methyladenine (3-MA), which inhibits autophagy and bafilomycin A1 (BFA), which inhibits lysosomes, significantly inhibited hippocampal neuronal damage after CA. These results indicate that CA affects both autophagy and apoptosis, partially mediated by p53. Autophagy plays a significant role in hippocampal neuronal death induced by cerebral I/R following asphyxial-CA.

Therapeutic Hypothermia Enhances Cold-Inducible RNA-Binding Protein Expression and Inhibits Mitochondrial Apoptosis in a Rat Model of Cardiac Arrest

Therapeutic hypothermia is well known for its protective effect against brain injury after cardiac arrest, but the exact mechanism remains unclear. Cold-inducible RNA-binding protein (CIRP), a member of cold shock protein, enables mammalian cells to withstand decreased temperature by regulating gene translation. However, the role of CIRP in global cerebral ischemia after therapeutic hypothermia has not been clearly elucidated. In the present study, rats resuscitated from 4 min of cardiac arrest were separately treated with therapeutic hypothermia (immediately after return of spontaneous circulation (ROSC); targeted temperature at 33 °C) and therapeutic normothermia (targeted temperature at 36.8 °C) for 6 h. The hippocampus was harvested at 0 h (baseline), 6 h, 12 h, 1 day, 3 days, and 7 days after ROSC. The expression of CIRP messenger RNA (mRNA) was assessed by real-time PCR. CIRP and mitochondrial apoptosis-associated proteins were tested by Western blot. The histological changes and neurological function were respectively evaluated by hematoxylin-eosin staining and neurological deficit score (NDS). Compared with baseline, rats resuscitated from cardiac arrest showed increased expression of CIRP, Bax, Caspase 9, and Caspase 3 and decreased expression of Bcl-2 in hippocampus (P < 0.05). However, therapeutic hypothermia after ROSC alleviated the alterations of Bax, Caspase 9, Caspase 3, and Bcl-2, while further increased the hippocampal expression of CIRP mRNA and protein, when compared with the normothermia rats (P < 0.05). In addition, compared with the therapeutic normothermia rats, histopathological damage in CA1 zone and NDS were respectively decreased and increased in the hypothermia rats (P < 0.05). Our findings suggest that 32 °C therapeutic hypothermia exerts an important neuroprotective effects by up-regulating CIRP expression and inhibiting mitochondrial apoptosis factor production in the cardiac arrest rat model.

Rapid and selective brain cooling method using vortex tube: A feasibility study

Vortex tubes are simple mechanical devices to produce cold air from a stream of compressed air without any moving parts. The primary focus of the current study is to investigate the feasibility and efficiency of nasopharyngeal brain cooling method using a vortex tube. Experiments were conducted on 5 juvenile pigs. Nasopharygeal brain cooling was achieved by directing cooled air via a catheter in each nostril into the nasal cavities. A vortex tube was used to generate cold air using various sources of compressed air: (I) hospital medical air outlet (n = 1); (II) medical air cylinders (n = 3); and (III) scuba (diving) cylinders (n = 1). By using compressed air from a hospital medical air outlet at fixed inlet pressure of 50 PSI, maximum brain-rectal temperature gradient of -2°C was reached about 45-60 minutes by setting the flow rate of 25 L/min and temperature of -7°C at the cold air outlet. Similarly, by using medical air cylinders at fill-pressure of 2265 PSI and down regulate the inlet pressure to the vortex tube to 50 PSI, brain temperature could be reduced more rapidly by blowing -22°C ± 2°C air at a flow rate of 50 L/min; brain-body temperature gradient of -8°C was obtained about 30 minutes. Furthermore, we examined scuba cylinders as a portable source of compressed gas supply to the vortex tube. Likewise, by setting up the vortex tube to have an inlet pressure of 25 PSI and 50 L/min and -3°C at the cold air outlet, brain temperature decreased 4.5°C within 10-20 min.

Therapeutic hypothermia in the intensive cardiac care unit

Therapeutic hypothermia has demonstrated to improve both survival and neurological outcome in patients who experienced an out-of-hospital cardiac arrest. Nevertheless, many aspects of its clinical application are still controversial. Current guidelines recommend to cool patients who survive a cardiac arrest due to either ventricular fibrillation or ventricular tachycardia, whereas the beneficial effect of lowering body temperature in nonshockable rhythms is still questionable due to the lack of randomized controlled trial involving this subgroup of patients. Although therapeutic hypothermia is often begun before hospital arrival, the optimal time to start cooling is still a matter of debate. Furthermore, different methods are available to low body temperature, but no direct comparisons are available to establish which device performs better than others, and a combination of external and endovascular cooling is usually preferred. The present review is aimed at summarizing the available evidence supporting the use in clinical practice of mild hypothermia in comatose survivors from cardiac arrest and at evaluating its adverse events and their treatment.

Prolonged Localized Mild Hypothermia Does Not Affect Seizure Activity After Intracerebral Hemorrhage in Rats

Intracerebral hemorrhage (ICH) is a devastating stroke with high morbidity and mortality. Post-ICH seizures are a common complication, potentially increasing brain injury and the risk of delayed epilepsy. Mild therapeutic hypothermia (HYPO, ∼33°C) is neuroprotective against several brain insults, such as ischemia, while also mitigating seizure incidence and severity in some instances. Therefore, we tested whether brain-selective HYPO reduced electrographic seizure activity after a collagenase-induced striatal ICH in rats. Animals were injected unilaterally with 0.14 U of bacterial collagenase, implanted with a unilateral brain cooling device, and a probe to bilaterally record electroencephalographic (EEG) activity. Cooling began 6 hours after collagenase infusion and was maintained for 48 hours, followed by rewarming over 6 hours. Our protocol did not affect EEG activity in naïve rats, nor did it increase bleeding after ICH (∼50 μL). Epileptiform activity commonly occurred in untreated ICH rats (∼60% of animals), but HYPO did not affect the incidence, timing, total duration of seizures, or the peaks occurring during epileptiform activity. However, longer average duration was detected on the ipsilateral side to stroke in the HYPO group (p < 0.05). Cooling did not affect neurological deficits (e.g., circling), measured 7 and 14 days after ICH, or lesion volume (∼35 mm(3)). In addition, there was no relationship among endpoints (e.g., seizures and lesion size). In summary, HYPO failed to reduce seizure activity after ICH, which fits with our separate findings that cooling does not mitigate thrombin and iron-mediated secondary injury mechanisms thought to cause seizures after ICH. Additional research is needed to identify better HYPO protocols and the use of cotreatments to maximize the benefit of HYPO to ICH patients.

The benefits of respective and combined use of green tea polyphenols and ERK inhibitor on the survival and neurologic outcomes in cardiac arrest rats induced by ventricular fibrillation

BACKGROUND

Cerebral injury is a main factor contributing to a high mortality after cardiac arrest (CA)/cardiopulmonary resuscitation (CPR).

OBJECTIVE

We sought to evaluate the effect of green tea polyphenols (GTPs) and ERK1/2 inhibitor PD98059 (PD) on the survival and neurologic outcomes after CA/CPR in rats.

METHODS

First, rats were subjected to CA after CPR. The rats that restored spontaneous circulation were blindly allocated to the saline group (saline, IV, n = 12), the GTP group (GTPs, 10 mg/kg, IV, n = 12), the PD group (PD, 0.3 mg/kg, IV, n = 12), and the GTPs + PD group (GTPs, 10 mg/kg; PD, 0.3 mg/kg, IV, n = 12). Another 12 rats without experiencing CA and CPR were served as a sham group. Survival and the neurologic deficit score were observed for 72 hours after restoration of spontaneous circulation. Second, same experimental procedures were performed, and in 1 of 5 groups, animals were divided into 4 subgroups further according to the different time points (12, 24, 48, and 72 hours after restoration of spontaneous circulation [ROSC], n = 6/group). Brain tissues were harvested at relative time points for the morphologic evaluation as well as reactive oxygen species (ROS), malonylaldehyde, and superoxide dismutase (SOD) measurement.

RESULTS

Green tea polyphenols, PD, and a combination of GTPs and PD used after ROSC alleviated the morphologic changes of the cerebrum. These 3 treatments also decreased the productions of ROS and malonylaldehyde, increased SOD activities in cerebral tissues, and improved the neurologic deficit and survival rates at 12, 24, 48, and 72 hours after ROSC.

CONCLUSIONS

Administration of GTPs and PD after ROSC can alleviate cerebral injury, improve the survival and neurologic outcomes via reduction of ROS, and increase of SOD activity in a rat CA/CPR model.

Early Quantitative Gamma-Band EEG Marker is Associated with Outcomes After Cardiac Arrest and Targeted Temperature Management

BACKGROUND

Brain recovery after cardiac arrest (CA) is sensitive to temperature. Yet the effect of temperature management on different EEG frequency bands has not been elucidated. A novel quantitative EEG algorithm, sub-band information quantity (SIQ), was applied to evaluate EEG recovery and outcomes after CA.

METHODS

Twenty-four Wistar rats undergoing 7-min CA were randomly assigned to immediate hypothermia (32-34 °C), normothermia (36.5-37.5 °C), or hyperthermia (38.5-39.5 °C) (n = 8). EEG was recorded continuously for the first 8 h and then for serial 30-min epochs daily. The neurologic deficit score (NDS) at 72-h was the primary functional outcome. Another four rats without brain injury were added as a control.

RESULTS

Better recovery of gamma-band SIQ was found in the hypothermia group (0.60 ± 0.03) compared with the normothermia group (0.40 ± 0.03) (p < 0.01) and in the normothermia group compared with the hyperthermia group (0.34 ± 0.03) (p < 0.05). The NDS was also improved in the lower temperature groups: hypothermia [median (25th, 75th), 74 (61, 74)] versus normothermia [49 (47, 61)] versus hyperthermia [43 (0, 50)] (p < 0.01). Throughout the 72-h experiment, the gamma-band SIQ showed the strongest correlation at every time point (ranging 0.520-0.788 from 30-min to 72-h post-resuscitation, all p < 0.05) whereas the delta-band SIQ had poor correlation with the 72-h NDS. No significant difference of sub-band EEG was found with temperature manipulation alone.

CONCLUSIONS

Recovery of gamma-band SIQ-qEEG was strongly associated with functional outcomes after CA. Induced hypothermia was associated with faster recovery of gamma-band SIQ and improved functional outcomes. Targeted temperature management primarily affected gamma frequency oscillations but not delta rhythm.

The science of reperfusion injury post cardiac arrest--Implications for emergency nurses

Survival following cardiac arrest in the developed world remains below 10%. In those who survive the initial cardiac arrest, prognosis remains poor due to the onset of multi-organ failure with both significant cardiac and neurological dysfunction. Nurses have demonstrated good understanding of cardiac arrest/post arrest guidelines and have good technical skills but deficits remain in their understanding of pathophysiological processes involved in post cardiac arrest syndromes. This article aims to provide an overview of these pathophysiological processes involved in the post cardiac arrest phase, potential treatment options and the nursing interventions that may be required within the emergency department setting. This article will focus emergency nurses to become more involved in patient management at this critical phase of treatment and highlight potential early signs of deterioration. Although return of spontaneous circulation (ROSC) is crucial in the process of recovery from cardiac arrest, it is only the first of many complex stages. Given the complexity of post cardiac arrest syndrome and its impact on the patient, healthcare professionals need to understand the cellular changes associated with reperfusion injuries in order to improve outcomes. It is only through effective nursing care and medical management that improved outcomes will become more common in the future.

Band specific changes in thalamocortical synchrony in field potentials after cardiac arrest induced global hypoxia

Cardiac Arrest (CA) leads to a global hypoxic-ischemic injury in the brain leading to a poor neurological outcome. Understanding the mechanisms of functional disruption in various regions of the brain may be essential for the development of improved diagnostic and therapeutic solutions. Using controlled laboratory experiment with animal models of CA, our primary focus here is on understanding the functional changes in the thalamus and the cortex, associated with the injury and acute recovery upon resuscitation. Specifically, to study the changes in thalamocortical synchrony through these periods, we acquired local field potentials (LFPs) from the ventroposterior lateral (VPL) nucleus of the thalamus and the forelimb somatosensory cortex (S1FL) in rats after asphyxial CA. Band-specific relative Hilbert phases were used to analyze synchrony between the LFPs. We observed that the CA induced global ischemia changes the local phase-relationships by introducing a phase-lag in both the thalamus and the cortex, while the synchrony between the two regions is nearly completely lost after CA.

Effect of hypothermia on cortical and thalamic signals in anesthetized rats

Beneficial effects of hypothermia on subjects with neuro-pathologies have been well demonstrated in both animal studies and clinical trials. Although it is known that temperature significantly impacts neurological injuries, the underlying mechanism remains unclear. We studied the effect of temperature modulation on neural signals in the cortex and the thalamus in uninjured brains of anesthetized rats. Six rats were divided into a hypothermic (32 to 34 °C, n=3) and a hyperthermic group (38.5 to 39.5 °C, n=3). EEG, and extracellular signals from somatosensory cortex and the ventral posterolateral nucleus of thalamus were recorded at different temperature phases (normothermia (36.5 to 37.5 °C) and hypothermia or hyperthermia). During hypothermia, similar burst suppression (BS) patterns were observed in cortical and thalamic signals as in EEG, but thalamic activity was not completely under suppression when both EEG and cortical signals were electrically silent. In addition, our results showed that hypothermia significantly increased the burst suppression ratio (BSR) in EEG, cortical and thalamic signals by 3.42, 3.25, 7.29 times respectively (P<0.01), and prolonged the latency of neuronal response in cortex to median nerve stimulation from 9 ms to 16 ms (P<0.01). Furthermore, during normothermia, the correlation coefficient between thalamic and cortical signals was 0.35±0.02 while during hypothermia, it decreased to 0.16±0.03 with statistical significance (P<0.01). These results can potentially assist in better understanding the effects of hypothermia.

Information-Theoretical Quantifier of Brain Rhythm Based on Data-Driven Multiscale Representation

This paper presents a data-driven multiscale entropy measure to reveal the scale dependent information quantity of electroencephalogram (EEG) recordings. This work is motivated by the previous observations on the nonlinear and nonstationary nature of EEG over multiple time scales. Here, a new framework of entropy measures considering changing dynamics over multiple oscillatory scales is presented. First, to deal with nonstationarity over multiple scales, EEG recording is decomposed by applying the empirical mode decomposition (EMD) which is known to be effective for extracting the constituent narrowband components without a predetermined basis. Following calculation of Renyi entropy of the probability distributions of the intrinsic mode functions extracted by EMD leads to a data-driven multiscale Renyi entropy. To validate the performance of the proposed entropy measure, actual EEG recordings from rats (n = 9) experiencing 7 min cardiac arrest followed by resuscitation were analyzed. Simulation and experimental results demonstrate that the use of the multiscale Renyi entropy leads to better discriminative capability of the injury levels and improved correlations with the neurological deficit evaluation after 72 hours after cardiac arrest, thus suggesting an effective diagnostic and prognostic tool.

Effect of valproic acid combined with therapeutic hypothermia on neurologic outcome in asphyxial cardiac arrest model of rats

BACKGROUNDS

Valproic acid (VPA) has been reported to have survival and neuroprotective effects in a cardiac arrest rat model. This study was designed to investigate the effect of VPA combined with therapeutic hypothermia (HT) in an asphyxial cardiac arrest rat model.

METHODS

Rats were subjected to 6 minutes of asphyxial cardiac arrest. Cardiopulmonary resuscitation was performed and then the randomly allocated to 1 of 4 groups (normal saline [NS]/normothermia [NT], VPA/NT, NS/HT, and VPA/HT). Hypothermia (32.5°C ± 0.5°C, 4 hours of HT and 2 hours of rewarming) or NT (37°C ± 0.5°C for 6 hours) was applied, and VPA (300 mg/kg) or NS was administered immediately after the return of spontaneous circulation. Neurologic deficit score was measured, and a tape removal test was performed for 3 days. Histologic injury of hippocampus was evaluated.

RESULTS

Valproic acid significantly improved neurologic deficit score at 48 and 72 hours in the NT-treated rats and at 72 hours in the HT-treated rats (all P < .05). Although the latency and success rate were not significantly different between the VPA/NT and NS/NT groups, the VPA/HT group showed significantly lower latency and higher success rates compared to the NS/HT group (P < .05). The histologic injury score in the hippocampal CA1 sector was significantly lower in the VPA/NT group than the NS/NT group (P < .05) and showed a tendency to be decreased in the VPA/HT group compared with the NS/HT group (P = .06).

CONCLUSION

In an asphyxial cardiac arrest rat model, administration of VPA improved neurologic outcomes and added a neuroprotective effect to HT.

Early prognostication markers in cardiac arrest patients treated with hypothermia

BACKGROUND AND PURPOSE

Established prognostication markers, such as clinical findings, electroencephalography (EEG) and biochemical markers, used by clinicians to predict neurological outcome after cardiac arrest (CA) are altered under therapeutic hypothermia (TH) conditions and their validity remains uncertain.

METHODS

MEDLINE and Embase were searched for evidence on the current standards for neurological outcome prediction for out-of-hospital CA patients treated with TH and the validity of a wide range of prognostication markers. Relevant studies that suggested one or several established biomarkers and multimodal approaches for prognostication are included and reviewed.

RESULTS

Whilst the prognostic accuracy of various tests after TH has been questioned, pupillary light reflexes and somatosensory evoked potentials are still strongly associated with negative outcome for early prognostication. Increasingly, EEG background activity has also been identified as a valid predictor for outcome after 72 h after CA and a preferred prognostic method in clinical settings. Neuroimaging techniques, such as magnetic resonance imaging and computed tomography, can identify functional and structural brain injury but are not readily available at the patient's bedside because of limited availability and high costs.

CONCLUSIONS

A multimodal algorithm composed of neurological examination, EEG-based quantitative testing and somatosensory evoked potentials, in conjunction with newer magnetic resonance imaging sequences, if available, holds promise for accurate prognostication in CA patients treated with TH. In order to avoid premature withdrawal of care, prognostication should be performed more than 72 h after CA.

What's New in Traumatic Brain Injury: Update on Tracking, Monitoring and Treatment

Traumatic brain injury (TBI), defined as an alteration in brain functions caused by an external force, is responsible for high morbidity and mortality around the world. It is important to identify and treat TBI victims as early as possible. Tracking and monitoring TBI with neuroimaging technologies, including functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), positron emission tomography (PET), and high definition fiber tracking (HDFT) show increasing sensitivity and specificity. Classical electrophysiological monitoring, together with newly established brain-on-chip, cerebral microdialysis techniques, both benefit TBI. First generation molecular biomarkers, based on genomic and proteomic changes following TBI, have proven effective and economical. It is conceivable that TBI-specific biomarkers will be developed with the combination of systems biology and bioinformation strategies. Advances in treatment of TBI include stem cell-based and nanotechnology-based therapy, physical and pharmaceutical interventions and also new use in TBI for approved drugs which all present favorable promise in preventing and reversing TBI.

Bench-to-Bedside and Bedside Back to the Bench; Seeking a Better Understanding of the Acute Pathophysiological Process in Severe Traumatic Brain Injury

Despite substantial investments, traumatic brain injury (TBI) remains one of the major disorders that lack specific pharmacotherapy. To a substantial degree, this situation is due to lack of understanding of the pathophysiological process of the disease. Experimental TBI research offers controlled, rapid, and cost-effective means to identify the pathophysiology but translating experimental findings into clinical practice can be further improved by using the same or similar outcome measures and clinically relevant time points. The pathophysiology during the acute phase of severe TBI is especially poorly understood. In this Mini review, I discuss some of the incongruences between current clinical practices and needs versus information provided by experimental TBI research as well as the benefits of designing animal experiments with translation into clinical practice in mind.

Targeted temperature management after out-of-hospital cardiac arrest: who, when, why, and how?

OBJECTIVE

To provide a succinct review of the evidence, framed for the emergency department clinician, for the application of targeted temperature management (TTM) for patients after out-of-hospital cardiac arrest (OHCA).

SOURCES OF INFORMATION

MEDLINE, EMBASE, and the Cochrane database were searched for prospective and retrospective studies relevant to the indications of TTM, optimal timing of TTM initiation, method of cooling, and target temperature.

MAIN MESSAGE

Two prospective interventional trials reported improved neurologically intact survival with the use of TTM (goal temperatures of 32°C to 34°C) compared with no temperature management in comatose OHCA patients with shockable initial cardiac arrest rhythms. A more recent, high-quality randomized controlled trial including OHCA patients with shockable and nonshockable initial rhythms compared TTM at 33°C versus TTM at 36°C. Despite the study being well powered, superiority of one target temperature over the other was not demonstrated. The benefit of TTM in patients with initial nonshockable rhythms is not clear; however, some observational studies have suggested benefit. There is no evidence that any particular method of temperature regulation is superior. The relationship between time and TTM initiation has not been well established.

CONCLUSION

Targeted temperature management, with a target temperature between 32°C and 36°C, as a component of comprehensive critical care is a beneficial intervention for comatose patients with return of spontaneous circulation after OHCA.

Targeted temperature management processes and outcomes after out-of-hospital cardiac arrest: an observational cohort study*

OBJECTIVES

Targeted temperature management has been shown to improve survival with good neurological outcome in patients after out-of-hospital cardiac arrest. The optimal approach to inducing and maintaining targeted temperature management, however, remains uncertain. The objective of this study was to evaluate these processes of care with survival and neurological function in patients after out-of-hospital cardiac arrest.

DESIGN

An observational cohort study evaluating the association of targeted temperature management processes with survival and neurological function using bivariate and generalized estimating equation analyses.

SETTING

Thirty-two tertiary and community hospitals in eight urban and rural regions of southern Ontario, Canada.

PATIENTS

Consecutive adult (≥ 18 yr) patients admitted between November 1, 2007, and January 31, 2012, and who were treated with targeted temperature management following nontraumatic out-of-hospital cardiac arrest.

INTERVENTIONS

Evaluate the association of targeted temperature management processes with survival and neurologic function using bivariate and generalized estimating equation analyses.

MEASUREMENTS AND MAIN RESULTS

There were 5,770 consecutive out-of-hospital cardiac arrest patients, of whom 747 (12.9%) were eligible and received targeted temperature management. Among patients with available outcome data, 365 of 738 (49.5%) survived to hospital discharge and 241 of 675 (35.7%) had good neurological outcomes. After adjusting for the Utstein variables, a higher temperature prior to initiation of targeted temperature management was associated with improved neurological outcomes (odds ratio, 1.27 per °C; 95% CI, 1.08-1.50; p = 0.004) and survival (odds ratio, 1.26 per °C; 95% CI, 1.09-1.46; p = 0.002). A slower rate of cooling was associated with improved neurological outcomes (odds ratio, 0.74 per °C/hr; 95% CI, 0.57-0.97; p = 0.03) and survival (odds ratio, 0.73 per °C/hr; 95% CI, 0.54-1.00; p = 0.049).

CONCLUSIONS

A higher baseline temperature prior to initiation of targeted temperature management and a slower rate of cooling were associated with improved survival and neurological outcomes. This may reflect a complex relationship between the approach to targeted temperature management and the extent of underlying brain injury causing impaired thermoregulation in out-of-hospital cardiac arrest patients.

The effects of local and general hypothermia on temperature profiles of the central nervous system following spinal cord injury in rats

Local and general hypothermia are used to treat spinal cord injury (SCI), as well as other neurological traumas. While hypothermia is known to provide significant therapeutic benefits due to its neuroprotective nature, it is unclear how the treatment may affect healthy tissues or whether it may cause undesired temperature changes in areas of the body that are not the targets of treatment. We performed 2-hour moderate general hypothermia (32°C core) or local hypothermia (30°C spinal cord) on rats that had received either a moderate contusive SCI or laminectomy (control) while monitoring temperatures at three sites: the core, spinal cord, and cortex. First, we identified that injured rats that received general hypothermia exhibited larger temperature drops at the spinal cord (-3.65°C, 95% confidence intervals [CIs] -3.72, -3.58) and cortex (-3.64°C, CIs -3.73, -3.55) than uninjured rats (spinal cord: -3.17°C, CIs -3.24, -3.10; cortex: -3.26°C, CIs -3.34, -3.17). This was found due to elevated baseline temperatures in the injured group, which could be due to inflammation. Second, both general hypothermia and local hypothermia caused a significant reduction in the cortical temperature (-3.64°C and -1.18°C, respectively), although local hypothermia caused a significantly lower drop in cortical temperature than general hypothermia (p<0.001). Lastly, the rates of rewarming of the cord were not significantly different among the methods or injury groups that were tested; the mean rate of rewarming was 0.13±0.1°C/min. In conclusion, local hypothermia may be more suitable for longer durations of hypothermia treatment for SCI to reduce temperature changes in healthy tissues, including the cortex.

Feasibility of bispectral index monitoring to guide early post-resuscitation cardiac arrest triage

INTRODUCTION

Triage after resuscitation from cardiac arrest is hindered by reliable early estimation of brain injury. We evaluated the performance of a triage model based on early bispectral index (BIS) findings and cardiac risk classes.

METHODS

Retrospective evaluation of serial patients resuscitated from cardiac arrest, unable to follow commands, and undergoing hypothermia. Patients were assigned to a cardiac risk group: STEMI, VT/VF shock, VT/VF no shock, or PEA/asystole, and to a neurological dysfunction group, based on the BIS score following first neuromuscular blockade (BISi), and classified as BISi>20, BISi 10-20, or BISi<10. Cause of death was described as neurological or circulatory.

RESULTS

BISi in 171 patients was measured at 267(±177)min after resuscitation and 35(±1.7)°C. BISi<10 suffered 82% neurological-cause and 91% overall mortality, BISi 10-20 35% neurological and 55% overall mortality, and BISi>20 12% neurological and 36% overall mortality. 33 patients presented with STEMI, 15 VT/VF-shock, 41 VT/VF-no shock, and 80 PEA/asystole. Among BISi>20 patients, 75% with STEMI underwent urgent cardiac catheterization (cath) and 94% had good outcome. When BISi>20 with VT/VF and shock, urgent cath was infrequent (33%), and 4 deaths (44%) were uniformly of circulatory etiology. Of 56 VT/VF patients without STEMI, 24 were BISi>20 but did not undergo urgent cath - 5(20.8%) of these had circulatory-etiology death. Circulatory-etiology death also occurred in 26.5% BIS>20 patients with PEA/asystole. When BISi<10, a neurological etiology death dominated independent of cardiac risk group.

CONCLUSIONS

Neurocardiac triage based on very early processed EEG (BIS) is feasible, and may identify patients appropriate for individualized post-resuscitation care. This and other triage models warrant further study.

Improved early postresuscitation EEG activity for animals treated with hypothermia predicted 96 hr neurological outcome and survival in a rat model of cardiac arrest

Purpose. To investigate the effect of hypothermia on 96 hr neurological outcome and survival by quantitatively characterizing early postresuscitation EEG in a rat model of cardiac arrest. Materials and Methods. In twenty male Sprague-Dawley rats, cardiac arrest was induced through high frequency transesophageal cardiac pacing. Cardiopulmonary resuscitation was initiated after 5 mins untreated arrest. Immediately after resuscitation, animals were randomized to either 2 hrs of hypothermia (N = 10) or normothermia (N = 10). EEG, ECG, aortic pressure, and core temperature were continuously recorded for 6 hrs. Neurological outcome was evaluated daily during the 96 hrs postresuscitation period. Results. No differences in the baseline measurements and resuscitation outcome were observed between groups. However, 96 hr neurological deficit score (204 ± 255 versus 500 ± 0, P = 0.005) and survival (6/10 versus 0/10, P = 0.011) were significantly better in the hypothermic group. Quantitative analysis of early postresuscitation EEG revealed that burst frequency and spectrum entropy were greatly improved in the hypothermic group and correlated with 96 hr neurological outcome and survival. Conclusion. The improved burst frequency during burst suppression period and preserved spectrum entropy after restoration of continuous background EEG activity for animals treated with hypothermia predicted favorable neurological outcome and survival in this rat model of cardiac arrest.

Niacin suppresses the mitogen-activated protein kinase pathway and attenuates brain injury after cardiac arrest in rats

OBJECTIVES

To determine whether niacin attenuates brain injury and improves neurological outcome after cardiac arrest in rats and if its therapeutic benefits are associated with suppression of the mitogen-activated protein kinase pathway.

DESIGN

Prospective laboratory study.

SETTING

University laboratory.

SUBJECTS

Male Sprague-Dawley rats (n=77).

INTERVENTIONS

After 6 minutes of no flow time induced by ventricular fibrillation, cardiopulmonary resuscitation was provided and return of spontaneous circulation was achieved. Animals were then administered vehicle, single low dose (360 mg/kg; at 1 hr postreturn of spontaneous circulation), single high dose (1080 mg/kg; at 1 hr), or repeated low dose of niacin (360 mg/kg/d for 3 d; at 1, 24, and 48 hr) through an orogastric tube.

MEASUREMENTS AND MAIN RESULTS

Neurologic deficit scales were scored at 24 hours, 72 hours, and 7 days postreturn of spontaneous circulation. Single high dose of niacin improved neurologic deficit scales at 48 hours and 7 days, and repeated low dose of niacin improved neurologic deficit scales at 7 days. Then, a separate set of animals were killed at 72 hours postreturn of spontaneous circulation, and brain tissues were harvested. Single high dose and repeated low dose of niacin attenuated cellular apoptosis and neuronal damage in hippocampal cornu ammonis 1 and decreased axonal injury and microglial activation in corpus callosum. They increased nicotinamide adenine dinucleotide, reduced nicotinamide adenine dinucleotide phosphate and reduced glutathione levels, and decreased malondialdehyde level in brain tissues. Furthermore, they suppressed the phosphorylations of p38 and c-Jun N-terminal kinase/stress-activated protein kinase and the cleavage of caspase 3. However, they failed to enhance extracellular signal-regulated kinases 1/2 phosphorylation.

CONCLUSIONS

Single high dose and repeated low dose of niacin attenuated brain injury and improved neurological outcome after cardiac arrest in rats. Their therapeutic benefits were associated with suppressions of the phosphorylations of p38 and c-Jun N-terminal kinase/stress-activated protein kinase and the cleavage of caspase 3.

Effect of hypothermia on the thalamocortical function in the rat model

Neuroprotective effects of hypothermia are well documented in many injuries of the central nervous system in animal models as well as clinical studies. However, the underlying mechanisms are not fully understood. An important yet unexplored background issue is the effect of hypothermic cooling on the regional functionality of the healthy CNS. In a pilot study with the rat model, we seek to characterize the effect of moderate bodily cooling on the thalamo-cortical (T-C) function. Multiunit activity (MUA) and local field potentials (LFPs) were recorded from the thalamus (VPL nucleus) and the somatosensory cortex (S1) for normothermic, mild hypothermic and mild hyperthermic conditions in healthy rats and the thalamo-cortical dynamics was characterized with Granger Causal Interaction (GCI). The GCI indicated that the thalamic driving of the cortical activity significantly increases in strength with bodily cooling and weakens with mild heating. These results could have important implications towards understanding of hypothermia.

Assessing thalamocortical functional connectivity with Granger causality

Assessment of network connectivity across multiple brain regions is critical to understanding the mechanisms underlying various neurological disorders. Conventional methods for assessing dynamic interactions include cross-correlation and coherence analysis. However, these methods do not reveal the direction of information flow, which is important for studying the highly directional neurological system. Granger causality (GC) analysis can characterize the directional influences between two systems. We tested GC analysis for its capability to capture directional interactions within both simulated and in vivo neural networks. The simulated networks consisted of Hindmarsh-Rose neurons; GC analysis was used to estimate the causal influences between two model networks. Our analysis successfully detected asymmetrical interactions between these networks ( , t -test). Next, we characterized the relationship between the "electrical synaptic strength" in the model networks and interactions estimated by GC analysis. We demonstrated the novel application of GC to monitor interactions between thalamic and cortical neurons following ischemia induced brain injury in a rat model of cardiac arrest (CA). We observed that during the post-CA acute period the GC interactions from the thalamus to the cortex were consistently higher than those from the cortex to the thalamus ( 1.983±0.278 times higher, p = 0.021). In addition, the dynamics of GC interactions between the thalamus and the cortex were frequency dependent. Our study demonstrated the feasibility of GC to monitor the dynamics of thalamocortical interactions after a global nervous system injury such as CA-induced ischemia, and offers preferred alternative applications in characterizing other inter-regional interactions in an injured brain.

Effect of valproic acid on survival and neurologic outcomes in an asphyxial cardiac arrest model of rats

AIM OF THE STUDY

Valproic acid (VPA) has been known to reduce neuronal injury, has anti-inflammatory and anti-apoptotic effects as a histone deacetylase (HDAC) inhibitor. Thus, this study was performed to investigate the effects of VPA on survival and neurological outcomes in an asphyxial cardiac arrest model of rats.

METHODS

Male Sprague-Dawley rats were subjected to asphyxial cardiac arrest. For survival study, rats were subjected to 450s of asphyxial cardiac arrest. Cardiopulmonary resuscitation (CPR) was performed and then rats were blindly allocated to one of two groups (control group, n=10; VPA group, n=10). Valproic acid (300mgkg(-1)) or vehicle (normal saline) was administered via tail vein immediately after return of spontaneous circulation (ROSC) and observed for 72h. For neurological outcome study, rats (n=7 for each group) were subjected to same experimental procedures except duration of cardiac arrest of 360s. Neurological deficit scale (NDS) score was measured every 24h after ROSC for 72h and was ranged from 0 (brain dead) to 80 (normal). Brain tissues were harvested at 72h for evaluation of apoptotic injury and acetylation status of histone H3.

RESULTS

In survival study, 2 rats in VPA group were excluded because cardiac arrest was not achieved in predetermined time. Thus, 10 rats were allocated to control group and 8 rats were allocated to VPA group. The survival rates at 72h after cardiac arrest were significantly higher in VPA group than in control group (6/8 in VPA group, 3/10 rats in control group; log rank test, p<0.05). In neurological outcome study, all rats survived for 72h and NDS at 72h were significantly higher in VPA group than in control group (p<0.05). In brain tissues, expressions of acetylated histone H3 were not significantly different. However, expressions of cleaved caspase-3 were significantly lower in VPA group than in control group (p<0.05).

CONCLUSION

VPA increased survival rates and improved neurologic outcome in asphyxial cardiac arrest model of rats while decreasing expressions of cleaved caspase-3.

Prehospital therapeutic hypothermia after cardiac arrest: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Therapeutic hypothermia has been recommended for the treatment of cardiac arrest patients who remain comatose after the return of spontaneous circulation. However, the optimal time to initiate therapeutic hypothermia remains unclear. The objective of the present study is to assess the effectiveness and safety of prehospital therapeutic hypothermia after cardiac arrest.

METHODS

Databases such as MEDLINE, Embase, and Cochrane Library were searched from their establishment date to May of 2012 to retrieve randomized control trials on prehospital therapeutic hypothermia after cardiac arrest. Thereafter, the studies retrieved were screened based on predefined inclusion and exclusion criteria. Data were extracted and the quality of the included studies was evaluated. A meta-analysis was performed by using the Cochrane Collaboration Review Manager 5.1.6 software.

RESULTS

Five studies involving 633 cases were included, among which 314 cases were assigned to the treatment group and the other 319 cases to the control group. The meta-analysis indicated that prehospital therapeutic hypothermia after cardiac arrest produced significant differences in temperature on hospital admission compared with in-hospital therapeutic hypothermia or normothermia (patient data; mean difference=-0.95; 95% confidence interval -1.15 to -0.75; I(2)=0%). However, no significant differences were observed in the survival to the hospital discharge, favorable neurological outcome at hospital discharge, and rearrest. The risk of bias was low; however, the quality of the evidence was very low.

CONCLUSION

This review demonstrates that prehospital therapeutic hypothermia after cardiac arrest can decrease temperature on hospital admission. On the other hand, regarding the survival to hospital discharge, favorable neurological outcome at hospital discharge, and rearrest, our meta-analysis and review produces non-significant results. Using the Grading of Recommendations, Assessment, Development and Evaluation methodology, we conclude that the quality of evidence is very low.

Hypothermia amplifies somatosensory-evoked potentials in uninjured rats

Temperature fluctuations significantly impact neurological injuries in intensive care units. As the benefits of therapeutic hypothermia continue to unfold, many of these discoveries are generated by studies in animal models undergoing experimental procedures under the influence of anesthetics. We studied the effect of induced hypothermia on neural electrophysiological signals of an uninjured brain in a rodent model while under isoflurane. Fourteen rats were divided into 2 groups (n=7 each), on the basis of electrode placement at either frontal-occipital or primary somatosensory cortical locations. Neural signals were recorded during normothermia (T=36.5 to 37.5°C), mild hypothermia (T=32 to 34°C), and hyperthermia (T=38.5 to 39.5°C). The burst-suppression ratio was used to evaluate electroencephalography (EEG), and amplitude-latency analysis was used to assess somatosensory-evoked potentials (SSEPs). Hypothermia was characterized by an increased burst-suppression ratio (mean±SD) of 0.58±0.06 in hypothermia versus 0.16±0.13 in normothermia, P<0.001 in frontal-occipital; and 0.30±0.13 in hypothermia versus 0.04±0.04 in normothermia, P=0.006 in somatosensory. There was potentiation of SSEP (2.89±1.24 times the normothermic baseline in hypothermia, P=0.02) and prolonged peak latency (N10: 10.8±0.4 ms in hypothermia vs. 9.1±0.3 ms in normothermia; P15: 16.2±0.8 ms in hypothermia vs. 13.7±0.6 ms in normothermia; P<0.001), whereas hyperthermia was primarily marked by shorter peak latencies (N10: 8.6±0.2 ms, P15: 12.6±0.4 m; P<0.001). In the absence of brain injury in a rodent model, hypothermia induces significant increase to the SSEP amplitude while increasing SSEP latency. Hypothermia also suppressed EEGs at different regions of the brain by different degrees. The changes to SSEP and EEG are both reversible with subsequent rewarming.

Outcome prediction by amplitude-integrated EEG in adults with hypoxic ischemic encephalopathy

INTRODUCTION

Amplitude-integrated electroencephalography (aEEG) had been widely used in predicting outcome in infants with hypoxic ischemic encephalopathy (HIE). We aimed to evaluate the use of aEEG as a quantitative predictor of outcome in adult patients with HIE.

METHODS

aEEG and Glasgow coma scale (GCS) were recorded for patients with HIE within 72 h of onset. aEEG traces were categorized as Grade I (normal amplitude): upper margin of aEEG activity >10 μV, lower margin >5 μV; Grade II (moderately abnormal amplitude): upper margin of aEEG activity >10 μV, lower margin ≤5 μV, or with suppressed amplitude, upper margin ≤10 μV, lower margin >5μV; Grade III (mild abnormality): either upper margin <10 μV, lower margin <5 μV. GCS was graded as I (9-14), grade II (4-8), or grade III (3). Cerebral performance category scores (CPCs) were determined 1 and 3 month after clinical evolution. CPC 1,2 were defined as favorable outcome; CPC 3,4,5 were considered as poor outcome.

RESULTS

30 cases met inclusion criteria. Both the aEEG grade and GCS scores correlated significantly with short-term outcome, and cases with a worse aEEG grade were more likely to have an unfavorable short-term outcome. Since the number of patients is really too small for long-term outcome analysis, we did not perform the analysis of aEEG, GCS and longer-term outcome. There was significant difference of clinical findings among aEEG classifications, while no statistical difference was found of causes of HIE.

CONCLUSIONS

aEEG is a reliable predictor of short-term outcome in HIE, and aEEG results within 72h after onset were associated with neurodevelopmental outcome at 1 mo following clinical evolution.

Hypoxic preconditioning attenuates global cerebral ischemic injury following asphyxial cardiac arrest through regulation of delta opioid receptor system

This study was designed to investigate whether delta opioid receptor (DOR) is involved in the neuroprotective effect induced by hypoxic preconditioning (HPC) in the asphyxial cardiac arrest (CA) rat model. Twenty-four hours after the end of 7-day HPC, the rats were subjected to 8-min asphyxiation and resuscitated with a standardized method. In the asphyxial CA rat model, HPC improved the neurological deficit score (NDS), inhibited neuronal apoptosis, and increased the number of viable hippocampal CA1 neurons at 24 h, 72 h, or 7 days after restoration of spontaneous circulation (ROSC); however, the above-mentioned neuroprotection of HPC was attenuated by naltrindole (a selective DOR antagonist). The expression of hypoxia-inducible factor-1α (HIF-1α) and DOR, and the content of leucine enkephalin (L-ENK) in the brain were also investigated after the end of 7-day HPC. HPC upregulated the neuronal expression of HIF-1α and DOR, and synchronously elevated the content of L-ENK in the rat brain. HIF-1α siRNA was used to further elucidate the relationship between HIF-1α and DOR in the HPC-treated brain. Knockdown of HIF-1α by siRNA markedly abrogated the HPC induced upregulation of HIF-1α and DOR. The present study demonstrates that the expression of DOR in the rat brain is upregulated by HIF-1α following exposure to 7-day HPC, at the same time, HPC also increases the production of endogenous DOR ligand L-ENK in the brain. DOR activation after HPC results in prolonged neuroprotection against subsequent global cerebral ischemic injury, suggesting a new mechanism of HPC-induced neuroprotection on global cerebral ischemia following CA and resuscitation.

Short- and long-latency somatosensory neuronal responses reveal selective brain injury and effect of hypothermia in global hypoxic ischemia

Evoked potentials recorded from the somatosensory cortex have been shown to be an electrophysiological marker of brain injury in global hypoxic ischemia (HI). The evoked responses in somatosensory neurons carry information pertaining to signal from the ascending pathway in both the subcortical and cortical areas. In this study, origins of the subcortical and cortical signals are explored by decomposing the evoked neuronal activities into short- and long-latency responses (SLR and LLR), respectively. We evaluated the effect of therapeutic hypothermia on SLR and LLR during early recovery from cardiac arrest (CA)-induced HI in a rodent model. Twelve rats were subjected to CA, after which half of them were treated with hypothermia (32-34°C) and the rest were kept at normal temperature (36-37°C). Evoked neuronal activities from the primary somatosensory cortex, including multiunit activity (MUA) and local field potential (LFP), were continuously recorded during injury and early recovery. Results showed that upon initiation of injury, LLR disappeared first, followed by the disappearance of SLR, and after a period of isoelectric silence SLR reappeared prior to LLR. This suggests that cortical activity, which primarily underlies the LLR, may be more vulnerable to ischemic injury than SLR, which relates to subcortical activity. Hypothermia potentiated the SLR but suppressed the LLR by delaying its recovery after CA (hypothermia: 38.83 ± 5.86 min, normothermia: 23.33 ± 1.15 min; P < 0.05) and attenuating its amplitude, suggesting that hypothermia may selectively downregulate cortical activity as an approach to preserve the cerebral cortex. In summary, our study reveals the vulnerability of the somatosensory neural structures to global HI and the differential effects of hypothermia on these structures.

Design of the RINSE trial: the rapid infusion of cold normal saline by paramedics during CPR

Background

The International Liaison Committee on Resuscitation (ILCOR) now recommends therapeutic hypothermia (TH) (33°C for 12-24 hours) as soon as possible for patients who remain comatose after resuscitation from shockable rhythm in out-of-hospital cardiac arrest and that it be considered for non shockable rhythms. The optimal timing of TH is still uncertain. Laboratory data have suggested that there is significantly decreased neurological injury if cooling is initiated during CPR. In addition, peri-arrest cooling may increase the rate of successful defibrillation. This study aims to determine whether paramedic cooling during CPR improves outcome compared standard treatment in patients who are being resuscitated from out-of-hospital cardiac arrest.

Methods/Design

This paper describes the methodology for a definitive multi-centre, randomised, controlled trial of paramedic cooling during CPR compared with standard treatment. Paramedic cooling during CPR will be achieved using a rapid infusion of large volume (20-40 mL/kg to a maximum of 2 litres) ice-cold (4°C) normal saline.

The primary outcome measure is survival at hospital discharge. Secondary outcome measures are rates of return of spontaneous circulation, rate of survival to hospital admission, temperature on arrival at hospital, and 12 month quality of life of survivors.

Discussion

This trial will test the effect of the administration of ice cold saline during CPR on survival outcomes. If this simple treatment is found to improve outcomes, it will have generalisability to prehospital services globally.

Trial Registration

ClinicalTrials.gov: NCT01172678

Time jitter of somatosensory evoked potentials in recovery from hypoxic-ischemic brain injury

Impaired neural conductivity shown by delayed latency and reduced amplitude of characteristic peaks in somatosensory evoked potentials (SSEPs), has been used to monitor hypoxic-ischemic brain injury after cardiac arrest (CA). However, rather than characteristic peak deferral and suppression, the time jitter of the peak in SSEP related with time-variant neurological abnormalities is diminished by the commonly used ensemble average method. This paper utilizes the second order blind identification (SOBI) technique to extract characteristic peak information from one trial of SSEPs. Sixteen male Wistar rats were subjected to 7 or 9 min of asphyxial CA (n=8 per group). The SSEPs from median nerve stimulation were recorded for 4h after CA and then for 15 min periods at 24, 48 and 72 h. Neurological outcomes were evaluated by neurologic deficit score (NDS) at 72 h post-CA. The SSEP signal was analyzed offline with SOBI processing in Matlab. The N10 feature of SSEP was compared between good (NDS≥50) and bad (NDS<50) outcomes. After processed by SOBI, the N10 detection rate was significantly increased (p<0.001) from 90 min post-CA. Statistical difference of the latency variance of the N10 between good and bad outcome groups existed at 24, 48 and 72 h post-CA (p≤0.001). Our study is the first application using SOBI detecting variance in neural signals like SSEP. N10 latency variance, related with neurophysiological dysfunction, increased after hypoxic-ischemic injury. The SOBI technique is an efficient method in the identification of peak detection and offers a favorable alternative to reveal the neural transmission variation.

Critical care of traumatic spinal cord injury

Approximately 11 000 people suffer traumatic spinal cord injury (TSCI) in the United States, each year. TSCI incidences vary from 13.1 to 52.2 per million people and the mortality rates ranged from 3.1 to 17.5 per million people. This review examines the critical care of TSCI. The discussion will focus on primary and secondary mechanisms of injury, spine stabilization and immobilization, surgery, intensive care management, airway and respiratory management, cardiovascular complication management, venous thromboembolism, nutrition and glucose control, infection management, pressure ulcers and early rehabilitation, pharmacologic cord protection, and evolving treatment options including the use of pluripotent stem cells and hypothermia.

Exploring high-frequency oscillation as a marker of brain ischemia using S-transform

Brain injury, such as hypoxic-ischemia produced in brain after cardiac arrest, is known to alter somatosensory evoked potential (SSEP) signals, thus serving a diagnostic role. This study explores the high-frequency oscillation (HFO) in SSEP recorded in a rat model of asphyxial cardiac arrest. To best characterize this complex oscillatory activity, several time-frequency representation strategies are implemented and compared. The S-transform (ST) is found to precisely localize the HFO in temporal-spectral space. More, the 'phase ST'-the inter-trial coherence (ITC) sensitively detects the phase-locked activities in HFO. Using ST and ITC, we explored the evolution of HFO during early recovery from brain injury. A discrepancy between the amplitude of HFO, which increases over time, and its phase, which stays time-invariant, is revealed here. The recovery dynamics of HFO mirrors that of N10 in terms of their amplitudes, which suggests HFO as a prelude of large-scale cortical responses. In addition, statistics shows the amplitudes of HFOs have different levels (p < 0.05) and recovery dynamics (p=0.03) between the good- and bad-outcome groups. We consider the HFO to be reflective of the health of thalamocotical circuitry in brain ischemia.

Study of the origin of short- and long-latency SSEP during recovery from brain ischemia in a rat model

Somatosensory evoked potentials (SSEPs) have been established as an electrophysiological tool for the prognostication of neurological outcome in patients with hypoxic-ischemic brain injury. The early and late responses in SSEPs reflect the sequential activation of neural structures along the somatosensory pathway. This study reports that the SSEP can be separated into early (short-latency, SL) and late (long-latency, LL) responses using independent component analysis (ICA), based on the assumption that these components are generated from different neural sources. Moreover, this source separation into the SL and LL components allows analysis of electrophysiological response to brain injury, even when the SSEPs are severely distorted and SL and LL components get mixed. With the help of ICA decomposition and corrected peak estimation, the latency of LL-SSEP is shown to be predictive of long-term neurological outcome. Further, it is shown that the recovery processes of SL- and LL-SSEPs follow different dynamics, with the SL-SSEP restored earlier than LL-SSEP. We predict that the SL- and LL-SSEPs reflect the timing of the progression of evoked response through the thalamocortical pathway and as such respond differently depending upon injury and recovery of the thalamic and cortical regions, respectively.