Delayed, spontaneous hypothermia reduces neuronal damage after asphyxial cardiac arrest in rats

Hypothermia After Cardiac Arrest in Large Animals (HACA-LA): Study protocol of a randomized controlled experimental trial

Background

Induced hypothermia post-cardiac arrest is neuroprotective in animal experiments, but few high-quality studies have been performed in larger animals with human-like brains. The neuroprotective effect of postischemic hypothermia has recently been questioned in human trials. Our aim is to investigate whether hypothermia post-cardiac arrest confers a benefit compared to normothermia in large adult animals. Our hypothesis is that induced hypothermia post cardiac arrest is neuroprotective and that the effect diminishes when delayed two hours.

Methods

Adult female pigs were anesthetized, mechanically ventilated and kept at baseline parameters including normothermia (38 °C). All animals were subjected to ten minutes of cardiac arrest (no-flow) by induced ventricular fibrillation, followed by four minutes of cardiopulmonary resuscitation with mechanical compressions, prior to the first countershock. Animals with sustained return of spontaneous circulation (systolic blood pressure >60 mmHg for ten minutes) within fifteen minutes from start of life support were included and randomized to three groups; immediate or delayed (2 h) intravenous cooling, both targeting 33 °C, or intravenously controlled normothermia (38 °C). Temperature control was applied for thirty hours including cooling time, temperature at target and controlled rewarming (0.5 °C/h). Animals were extubated and kept alive for seven days. The primary outcome measure is histological brain injury on day seven. Secondary outcomes include neurological and neurocognitive recovery, and the trajectory of biomarkers of brain injury.

Conclusion

High-quality animal experiments in clinically relevant large animal models are necessary to close the gap of knowledge regarding neuroprotective effects of induced hypothermia after cardiac arrest.Trial registration:Preclinicaltrials.eu (PCTE0000272), published 2021-11-03.

Differential Effects of Targeted Temperature Management on Sex-Dependent Outcomes After Experimental Asphyxial Cardiac Arrest

Asphyxial cardiac arrest (ACA) survivors face lasting neurological disability from hypoxic ischemic brain injury. Sex differences in long-term outcomes after cardiac arrest (CA) are grossly understudied and underreported. We used rigorous targeted temperature management (TTM) to understand its influence on survival and lasting sex-specific neurological and neuropathological outcomes in a rodent ACA model. Adult male and female rats underwent either sham or 5-minute no-flow ACA with 18 hours TTM at either ∼37°C (normothermia) or ∼36°C (mild hypothermia). Survival, temperature, and body weight (BW) were recorded over the 14-day study duration. All rats underwent neurological deficit score (NDS) assessment on days 1-3 and day 14. Hippocampal pathology was assessed for cell death, degenerating neurons, and microglia on day 14. Although ACA females were less likely to achieve return of spontaneous circulation (ROSC), post-ROSC physiology and biochemical profiles were similar between sexes. ACA females had significantly greater 14-day survival, NDS, and BW recovery than ACA males at normothermia (56% vs. 29%). TTM at 36°C versus 37°C improved 14-day survival in males, producing similar survival in male (63%) versus female (50%). There were no sex or temperature effects on CA1 histopathology. We conclude that at normothermic conditions, sex differences favoring females were observed after ACA in survival, NDS, and BW recovery. We achieved a clinically relevant ACA model using TTM at 36°C to improve long-term survival. This model can be used to more fully characterize sex differences in long-term outcomes and test novel acute and chronic therapies.

Rat model of asphyxia-induced cardiac arrest and resuscitation

Neurologic injury after cardiopulmonary resuscitation is the main cause of the low survival rate and poor quality of life among patients who have experienced cardiac arrest. In the United States, as the American Heart Association reported, emergency medical services respond to more than 347,000 adults and more than 7,000 children with out-of-hospital cardiac arrest each year. In-hospital cardiac arrest is estimated to occur in 9.7 per 1,000 adult cardiac arrests and 2.7 pediatric events per 1,000 hospitalizations. Yet the pathophysiological mechanisms of this injury remain unclear. Experimental animal models are valuable for exploring the etiologies and mechanisms of diseases and their interventions. In this review, we summarize how to establish a standardized rat model of asphyxia-induced cardiac arrest. There are four key focal areas: (1) selection of animal species; (2) factors to consider during modeling; (3) intervention management after return of spontaneous circulation; and (4) evaluation of neurologic function. The aim was to simplify a complex animal model, toward clarifying cardiac arrest pathophysiological processes. It also aimed to help standardize model establishment, toward facilitating experiment homogenization, convenient interexperimental comparisons, and translation of experimental results to clinical application.

Therapeutic Administration of Oxcarbazepine Saves Cerebellar Purkinje Cells from Ischemia and Reperfusion Injury Induced by Cardiac Arrest through Attenuation of Oxidative Stress

Research reports using animal models of ischemic insults have demonstrated that oxcarbazepine (a carbamazepine analog: one of the anticonvulsant compounds) extends neuroprotective effects against cerebral or forebrain injury induced by ischemia and reperfusion. However, research on protective effects against ischemia and reperfusion cerebellar injury induced by cardiac arrest (CA) and the return of spontaneous circulation has been poor. Rats were assigned to four groups as follows: (Groups 1 and 2) sham asphyxial CA and vehicle- or oxcarbazepine-treated, and (Groups 3 and 4) CA and vehicle- or oxcarbazepine-treated. Vehicle (0.3% dimethyl sulfoxide/saline) or oxcarbazepine (200 mg/kg) was administered intravenously ten minutes after the return of spontaneous circulation. In this study, CA was induced by asphyxia using vecuronium bromide (2 mg/kg). We conducted immunohistochemistry for calbindin D-28kDa and Fluoro-Jade B histofluorescence to examine Purkinje cell death induced by CA. In addition, immunohistochemistry for 4-hydroxy-2-nonenal (4HNE) was carried out to investigate CA-induced oxidative stress, and immunohistochemistry for Cu, Zn-superoxide dismutase (SOD1) and Mn-superoxide dismutase (SOD2) was performed to examine changes in endogenous antioxidant enzymes. Oxcarbazepine treatment after CA significantly increased the survival rate and improved neurological deficit when compared with vehicle-treated rats with CA (survival rates ≥ 63.6 versus 6.5%), showing that oxcarbazepine treatment dramatically protected cerebellar Purkinje cells from ischemia and reperfusion injury induced by CA. The salvation of the Purkinje cells from ischemic injury by oxcarbazepine treatment paralleled a dramatic reduction in 4HNE (an end-product of lipid peroxidation) and increased or maintained the endogenous antioxidant enzymes (SOD1 and SOD2). In brief, this study shows that therapeutic treatment with oxcarbazepine after CA apparently saved cerebellar neurons (Purkinje cells) from CA-induced neuronal death by attenuating oxidative stress and suggests that oxcarbazepine can be utilized as a therapeutic medicine for ischemia and reperfusion brain (cerebellar) injury induced by CA.

Dexmedetomidine post-conditioning attenuates cerebral ischemia following asphyxia cardiac arrest through down-regulation of apoptosis and neuroinflammation in rats

Background

Neuroprotection strategies after cardiac arrest (CA)/cardiopulmonary resuscitation (CPR) remain key areas of basic and clinical research. This study was designed to investigate the neuroprotective effects of dexmedetomidine following resuscitation and potential mechanisms.

Methods

Anesthetized rats underwent 6-min asphyxia-based cardiac arrest and resuscitation, after which the experimental group received a single intravenous dose of dexmedetomidine (25 μg/kg). Neurological outcomes and ataxia were assessed after the return of spontaneous circulation. The serum levels and brain expression of inflammation markers was examined, and apoptotic cells were quantified by TUNEL staining.

Results

Neuroprotection was enhanced by dexmedetomidine post-conditioning after the return of spontaneous circulation. This enhancement was characterized by the promotion of neurological function scores and coordination. In addition, dexmedetomidine post-conditioning attenuated the serum levels of the pro-inflammatory cytokine tumor necrosis factor (TNF)-α at 2 h, as well as interleukin IL-1β at 2, 24, and 48 h. TUNEL staining showed that the number of apoptotic cells in the dexmedetomidine post-conditioning group was significantly reduced compared with the control group. Further western blot analysis indicated that dexmedetomidine markedly reduced the levels of caspase-3 and nuclear factor-kappa B (NF-κB) in the brain.

Conclusions

Dexmedetomidine post-conditioning had a neuroprotective effect against cerebral injury following asphyxia-induced cardiac arrest. The mechanism was associated with the downregulation of apoptosis and neuroinflammation.

A novel ultrasound-guided mouse model of sudden cardiac arrest

AIM

Mouse models of sudden cardiac arrest are limited by challenges with surgical technique and obtaining reliable venous access. To overcome this limitation, we sought to develop a simplified method in the mouse that uses ultrasound-guided injection of potassium chloride directly into the heart.

METHODS

Potassium chloride was delivered directly into the left ventricular cavity under ultrasound guidance in intubated mice, resulting in immediate asystole. Mice were resuscitated with injection of epinephrine and manual chest compressions and evaluated for survival, body temperature, cardiac function, kidney damage, and diffuse tissue injury.

RESULTS

The direct injection sudden cardiac arrest model causes rapid asystole with high surgical survival rates and short surgical duration. Sudden cardiac arrest mice with 8-min of asystole have significant cardiac dysfunction at 24 hours and high lethality within the first seven days, where after cardiac function begins to improve. Sudden cardiac arrest mice have secondary organ damage, including significant kidney injury but no significant change to neurologic function.

CONCLUSIONS

Ultrasound-guided direct injection of potassium chloride allows for rapid and reliable cardiac arrest in the mouse that mirrors human pathology without the need for intravenous access. This technique will improve investigators' ability to study the mechanisms underlying post-arrest changes in a mouse model.

[A new method for establishing a ventricular fibrillation model by TCEI in Tibetan miniature pig]

OBJECTIVE

To explore an economical, convenient, safe and efficient method for establishing a Tibetan miniature pig model of cardiac arrest (CA).

METHODS

Cardiac puncture was performed in 12 Tibetan miniature pigs using two acupuncture needles. One needle was inserted into the fourth intercostal near the right side of the sternum about 3 cm in depth at an angle of 30° to 60° between the chest and the needle, and the depth was adjusted until the handle of the needle vibrated with the heartbeat without premature ventricular contraction on the electrocardiogram; the other was inserted into the subcutaneous tissue of the left armpit about 3 cm in depth without damaging important organs. The handles of the two needles were connected with 9V dry batteries to form a circuit and generate direct current stimulation. Ventricular fibrillation was produced in the pigs to induce CA by stimulation of transcutaneous electrical induction (TCEI) for 3 s, and the success rate of modeling was recorded. After an interval of 4 min without intervention, cardiopulmonary resuscitation (CPR) was performed using the standard Utstein style, and the survival of the pigs after recovery was observed.

RESULTS

The success rate of ventricular fibrillation modeling was 91.67% (11/12) using this method, and CPR achieved a success rate of 45.45% (5/11) in these models. The subsequent survival of the pigs was 100% (5/5) at 24 h and 80% (4/5) at 72 h. After observation for 72 h, the resuscitated Tibetan miniature pigs were dissected, and no significant damage was found in the vital organs in the thoracic or abdominal cavities.

CONCLUSIONS

We successfully established a model of CA using acupuncture needles and dry batteries in Tibetan miniature pigs, and this method is economical, convenient, safe and efficient.

PD98059 protects the brain against mitochondrial-mediated apoptosis and autophagy in a cardiac arrest rat model

AIMS

Mitochondrial dysfunction has been regarded as one of the hallmarks of cerebral ischemia-reperfusion injury. In previous studies, we have provided evidence that the extracellular signaling pathway (ERK) 1/2 inhibitor PD98059 improved the neurological deficits by modulating antioxidant and anti-apoptotic activities in rats subjected to cardiac arrest/cardiopulmonary resuscitation (CA/CPR). Since oxidative stress can activate mitochondria-dependent apoptosis and autophagy, we further explored the effects of PD98059 on mitochondria involved with apoptosis and autophagy in rat CA model.

MATERIALS AND METHODS

We disposed PD98059 in CA/CPR rats, tested the mitochondrial-mediated apoptosis pathway in brain tissues at 24 h post-resuscitation by mitochondrial permeability transition pores (MPTP), cytochrome c (CytC), BCL-2, BAX, caspase-3, as well as autophagy by LC3, Beclin-1, and p62. Furthermore, we explored the relationship of dynamin-related protein 1 (Drp1) with apoptosis and autophagy.

KEY FINDINGS

Our study showed that PD98059 decreased the openings of MPTP, CytC release, caspase3 activation, apoptotic indices, LC3-II, Beclin-1and increased P62. PD98059 also inhibited mitochondria-dependent apoptosis and the activity of autophagy in a dose-dependent manner in rat cerebral cortices at 24 h post-resuscitation. The generation of phosphorylated Drp1-616 was down-regulated accompanied by a decrease of TUNEL-positive cells and LC3 in dual immunostaining after PD98059 inhibited activation of ERK signaling pathway in a dose-dependent manner in rat cerebral cortices at 24 h post-resuscitation.

SIGNIFICANCE

PD98059 protects the brain against mitochondrial-mediated apoptosis and autophagy at 24 h post-resuscitation in rats subjected to CA/CPR, which is linked with the downregulation of Drp1 expression.

Therapeutic hypothermia attenuates paraplegia and neuronal damage in the lumbar spinal cord in a rat model of asphyxial cardiac arrest

Spinal cord ischemia can result from cardiac arrest. It is an important cause of severe spinal cord injury that can lead to serious spinal cord disorders such as paraplegia. Hypothermia is widely acknowledged as an effective neuroprotective intervention following cardiac arrest injury. However, studies on effects of hypothermia on spinal cord injury following asphyxial cardiac arrest and cardiopulmonary resuscitation (CA/CPR) are insufficient. The objective of this study was to examine effects of hypothermia on motor deficit of hind limbs of rats and vulnerability of their spinal cords following asphyxial CA/CPR. Experimental groups included a sham group, a group subjected to CA/CPR, and a therapeutic hypothermia group. Severe motor deficit of hind limbs was observed in the control group at 1 day after asphyxial CA/CPR. In the hypothermia group, motor deficit of hind limbs was significantly attenuated compared to that in the control group. Damage/death of motor neurons in the lumbar spinal cord was detected in the ventral horn at 1 day after asphyxial CA/CPR. Neuronal damage was significantly attenuated in the hypothermia group compared to that in the control group. These results indicated that therapeutic hypothermia after asphyxial CA/CPR significantly reduced hind limb motor dysfunction and motoneuronal damage/death in the ventral horn of the lumbar spinal cord following asphyxial CA/CPR. Thus, hypothermia might be a therapeutic strategy to decrease motor dysfunction by attenuating damage/death of spinal motor neurons following asphyxial CA/CPR.

Intraischemic Modest Hypothermia Does Not Prevent Onset of Locomotor Inactivity After Transient Forebrain Ischemia in Rats

Although modest hypothermia of 35°C has been demonstrated to provide histological neuroprotection in a rodent model of cerebral ischemia, the long-term behavioral outcome is still not clear. This study was designed to investigate whether modest hypothermia of 35°C provides sustained histological and behavioral neuroprotection following transient forebrain ischemia in rats. Male Sprague-Dawley rats were randomly assigned to one of three groups: sham, control, and modest hypothermia group. Each group contained eight rats. Ten-minute transient forebrain ischemia was produced by bilateral carotid artery occlusion plus hemorrhagic hypotension (mean arterial pressure = 40 mmHg). The hypothermic group was cooled to 35°C in preischemic period, and the cooling was continued for 1 hour postischemia. To evaluate behavioral outcome, spontaneous alternation behavior and locomotor activity were assessed using Y-maze test on a weekly basis. The rats were sacrificed after 28 days, and the number of intact neurons per 1 mm in the hippocampal CA1 subfield was counted microscopically. There was significant difference between the control [19(24.5)/mm: median (interquartile range)] and hypothermia groups [116(24)/mm; p < 0.01] in the intact CA1 neuron count. In the control and modest hypothermia groups, the locomotor activities were gradually decreased, and reached significantly lower levels in comparison with the sham group at 14 days postischemia. This study indicates that intraischemic modest hypothermia provided long-term histological neuroprotection, but did not reverse the onset of locomotor inactivity in a rat transient forebrain ischemia model.

Melatonin improves neurological outcomes and preserves hippocampal mitochondrial function in a rat model of cardiac arrest

Cerebral injury after cardiac arrest (CA)/cardiopulmonary resuscitation (CPR) has been implicated in the poor prognosis of CA survivors. This study was designed to evaluate the impact of melatonin on postresuscitation neurological outcomes and to explore the underlying mechanism. Sprague-Dawley rats were randomly assigned to four groups: sham group, CPR group, melatonin pretreatment group (Pre-M) and posttreatment group (Post-M). For the last 2 groups, daily melatonin gavage was performed for 12 consecutive days before or 24 hours after rat survival from CA/CPR. No statistical differences were observed in heart rate (HR), mean arterial blood pressure (MAP), and end-tidal carbon dioxide (_ETCO₂) at baseline and after restoration of spontaneous circulation (ROSC) among groups. However, melatonin pretreatment or posttreatment significantly improved neurological deficit score and memory and spatial learning ability after CA/CPR. Further studies demonstrated that the complex I- and complex-II supported mitochondrial respiration were greatly increased under melatonin treatment. In addition, melatonin treatment preserved the mitochondrial-binding hexokinase II (HKII) and ATP levels and suppressed the upregulated protein lysine acetylation in hippocampus after CA/CPR. In conclusion, using a rat asphyxial CA model we have demonstrated that treatment with melatonin either before or after CA/CPR provides a promising neuroprotective effect, and this protection was mediated by increasing mitochondrial HKII expression, suppressing protein acetylation and improving mitochondrial function in hippocampus.

Spontaneous hypothermia ameliorated inflammation and neurologic deficit in rat cardiac arrest models following resuscitation

Cardiac arrest (CA) is a leading cause of mortality worldwide. The majority of the associated mortalities are caused by post-CA syndrome, which includes symptoms, such as neurologic damage, myocardial dysfunction and systemic inflammation. Following CA, return of spontaneous circulation (ROSC) leads to a brain reperfusion injury, which subsequently causes adverse neurologic outcomes or mortality. Therefore, investigating the underlying mechanisms of ROSC-induced neurologic deficits and establishing potential treatments is critical to prevent and treat post-CA syndrome. In the current study, CA rat models were established by asphyxia. Following ROSC, the temperature was controlled to achieve hypothermia. The general neurologic status was assessed using the neurologic deficit scale. Changes in the concentrations of interleukin (IL)-18 and IL-1β were measured with ELISA and the dynamic change in NACHT, LRR and PYD domains-containing protein 3 inflammasome components was determined by western blot analysis and immunohistochemistry. Neuronal death and apoptosis were measured via TUNEL assays. In the CA rat models, increasing the duration of CA before cardiopulmonary resuscitation was found to aggravate the neural deficit and increase the incidence of inflammation. Following ROSC, the expression level of the inflammasome components was observed to increase in CA rat models, which was accompanied by increased secretion of IL-18 and IL-1β, indicating the promotion of inflammation. In addition, the study identified the beneficial role of spontaneous hypothermia in ameliorating the ROSC-induced inflammation and neurologic deficit in CA rat models, including the downregulation of inflammasome components and attenuating neuronal apoptosis. The present study contributes to the understanding of underlying mechanisms in CA-evoked inflammation and the subsequent neurologic damage following ROSC. A novel potential therapeutic strategy that may increase survival times and the quality of life for patients suffering from post-CA syndrome is proposed in the present study.

Rosuvastatin improves myocardial and neurological outcomes after asphyxial cardiac arrest and cardiopulmonary resuscitation in rats

Rosuvastatin, a potent HMG-CoA reductase inhibitor, is cholesterol-lowering drugs and reduce the risk of myocardial infarction and stroke. This study is to explore whether rosuvastatin improves outcomes after cardiac arrest in rats. Male Sprague-Dawley rats were subjected to 8min of cardiac arrest (CA) by asphyxia and randomly assigned to three experimental groups immediately following successful resuscitation: Sham; Control; and Rosuvastatin. The survival, hemodynamics, myocardial function, neurological outcomes and apoptosis were assessed. The 7-d survival rate was greater in the rosuvastatin treated group compared to the Control group (P=0.019 by log-rank test). Myocardial function, as measured by cardiac output and ejection fraction, was significantly impaired after CA and notably improved in the animals treated with rosuvastatin beginning at 60min after return of spontaneous circulation (ROSC) (P<0.05). Moreover, rosuvastatin treatment significantly ameliorated brain injury after ROSC, which was characterized by the increase of neurological function scores, and reduction of brain edema in cortex and hippocampus (P<0.05). Meanwhile, the levels of cardiac troponin T and neuron-specific enolase and the caspase-3 activity were significantly decreased in the Rosuvastatin group when compared with the Control group (P<0.05). In conclusion, rosuvastatin treatment substantially improves the 7-d survival rate as well as myocardial function and neurological outcomes after ROSC.

Mechanistic characterization of nitrite-mediated neuroprotection after experimental cardiac arrest

Nitrite acts as an ischemic reservoir of nitric oxide (NO) and a potent S-nitrosating agent which reduced histologic brain injury after rat asphyxial cardiac arrest (ACA). The mechanism(s) of nitrite-mediated neuroprotection remain to be defined. We hypothesized that nitrite-mediated brain mitochondrial S-nitrosation accounts for neuroprotection by reducing reperfusion reactive oxygen species (ROS) generation. Nitrite (4 μmol) or placebo was infused IV after normothermic (37°C) ACA in randomized, blinded fashion with evaluation of neurologic function, survival, brain mitochondrial function, and ROS. Blood and CSF nitrite were quantified using reductive chemiluminescence and S-nitrosation by biotin switch. Direct neuroprotection was verified in vitro after 1 and 4 h neuronal oxygen glucose deprivation measuring neuronal death with inhibition studies to examine mechanism. Mitochondrial ROS generation was quantified by live neuronal imaging using mitoSOX. Nitrite significantly reduced neurologic disability after ACA. ROS generation was reduced in brain mitochondria from nitrite- versus placebo-treated rats after ACA with congruent preservation of brain ascorbate and reduction of ROS in brain sections using immuno-spin trapping. ATP generation was maintained with nitrite up to 24 h after ACA. Nitrite rapidly entered CSF and increased brain mitochondrial S-nitrosation. Nitrite reduced in vitro mitochondrial superoxide generation and improved survival of neurons after oxygen glucose deprivation. Protection was maintained with inhibition of soluble guanylate cyclase but lost with NO scavenging and ultraviolet irradiation. Nitrite therapy results in direct neuroprotection from ACA mediated by reductions in brain mitochondrial ROS in association with protein S-nitrosation. Neuroprotection is dependent on NO and S-nitrosothiol generation, not soluble guanylate cyclase.

Temperature Control in Rodent Neuroprotection Studies: Methods and Challenges

Extensive animal research facilitated the clinical translation of therapeutic hypothermia for cardiac arrest in adults and hypoxic-ischemic injury in infants. Similarly, clinical interest in hypothermia for other brain injuries, such as stroke, has been greatly supported by positive findings in preclinical work. The reliability, validity, and utility of animal models, among many research practices (blinding, randomization, etc.), are key to successful clinical translation. Here, we review methods used to induce and maintain hypothermia in animal models. These include physical and pharmacological methods. We emphasize the advantages and limitations of each approach, and the importance of using clinically relevant cooling protocols and appropriate monitoring and reporting approaches. Moreover, we performed a literature survey of ischemic stroke studies published in 2015 to highlight the continuing risk of temperature confounds in neuroprotection studies. For example, many still do not accurately monitor and report temperature during surgery (23.5%), even though almost half of these studies (46.0%) use pharmaceutical agents that likely influence temperature. We hope this review stimulates awareness and discussion of the importance of temperature in neuroprotective studies.

Early Prognosticators for Induction of Therapeutic Hypothermia Following Cardiac Arrest

The American Heart Association recommends therapeutic hypothermia for comatose patients with return of spontaneous circulation after out-of-hospital ventricular fibrillation cardiac arrest. While there is a growing body of evidence for the general efficacy of therapeutic hypothermia, the individualized benefit of therapy is not currently predictable. Ninety-one consecutive patients, from April 2011 to July 2014, were treated at the University of Kentucky Medical Center with the therapeutic hypothermia protocol. Medical records were reviewed retrospectively. Data, such as preexisting comorbidities, cardiac arrest characteristics, and hospital course, were used to compose a multivariate logistic regression with mortality serving as the primary endpoint. The overall in-hospital mortality was 64% (n = 58) in this group. The arrest was considered cardiac etiology in 84% (n = 76) of patients, of which 49% (n = 45) were classed as ventricular fibrillation and 9% (n = 8) as ventricular tachycardia. The presence of a shockable rhythm, as well as shorter duration of cardiac arrest, was associated with increased survival, whereas time to target temperature was not. The presence of a preexisting neurologic disease was associated with a 10-fold increase in estimated odds of mortality. Age, serum lactate, ionized calcium, arterial pH, estimated glomerular filtration rate, and APACHE score were all predictors of mortality. Cardiac arrest is a devastating condition with a high mortality rate. Given the limited resources of the resuscitation community, the ability to predict survivors based on routinely obtained measures upon admission would be of tremendous value. In this study, we show a series of admission parameters that demonstrate predictive ability in identifying patients more likely to survive with therapeutic hypothermia.

Glibenclamide Improves Survival and Neurologic Outcome After Cardiac Arrest in Rats

OBJECTIVES

Glibenclamide confers neuroprotection in animal models as well as in retrospective clinical studies. This study determines whether glibenclamide improves outcome after cardiac arrest in rats.

DESIGN

Prospective randomized laboratory study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats (n = 126).

INTERVENTIONS

Rats successfully resuscitated from 8-minute asphyxial cardiac arrest were randomized to glibenclamide or vehicle group. Rats in the glibenclamide group were intraperitoneally administered glibenclamide with a loading dose of 10 μg/kg at 10 minutes and a maintenance dose of 1.2 μg at 6, 12, 18, and 24 hours after return of spontaneous circulation, whereas rats in the vehicle group received equivalent volume of vehicle solution.

MEASUREMENTS AND MAIN RESULTS

Survival was recorded every day, and neurologic deficit scores were assessed at 24, 48, and 72 hours and 7 days after return of spontaneous circulation (n = 22 in each group). Results showed that glibenclamide treatment increased 7-day survival rate, reduced neurologic deficit scores, and prevented neuronal loss in the hippocampal cornu ammonis 1 region. To investigate the neuroprotective effects of glibenclamide in acute phase, we observed neuronal injury at 24 hours after return of spontaneous circulation and found that glibenclamide significantly decreased the rate of neuronal necrosis and apoptosis. In addition, glibenclamide reduced the messenger RNA expression of tumor necrosis factor-α and monocyte chemoattractant protein-1 in the cortex after return of spontaneous circulation. Furthermore, the sulfonylurea receptor 1 and transient receptor potential M4 heteromers, the putative therapeutic targets of glibenclamide, were up-regulated after cardiac arrest and cardiopulmonary resuscitation, indicating that they might be involved in neuroprotective effect of glibenclamide.

CONCLUSIONS

Glibenclamide treatment substantially improved survival and neurologic outcome throughout a 7-day period after return of spontaneous circulation. The salutary effects of glibenclamide were associated with suppression of neuronal necrosis and apoptosis, as well as inflammation in the brain.

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.

Hyperbaric oxygen effects on neuronal apoptosis associations in a traumatic brain injury rat model

BACKGROUND

The neuroprotective mechanisms of hyperbaric oxygen (HBO) therapy on traumatic brain injury (TBI) remain unclear, especially neuronal apoptosis associations such as the expression of tumor necrosis factor alpha (TNF-α), transforming growth-interacting factor (TGIF), and TGF-β1 after TBI. The aim of this study was to investigate the neuroprotective effects of HBO therapy in a rat model of TBI.

MATERIALS AND METHODS

The experimental rats were randomly divided into three groups as follows: TBI + normobaric air (21% O₂ at one absolute atmosphere), TBI + HBO, and sham-operated normobaric air. The TBI + HBO rats received 100% O₂ at 2.0 absolute atmosphere for 1 h immediately after TBI. Local and systemic TNF-α expression, neuropathology, levels of the neuronal apoptosis-associated proteins TGIF and TGF-β1, and functional outcome were evaluated 72 h after the onset of TBI.

RESULTS

Compared to the TBI control groups, the running speed of rats on the TreadScan after TBI was significantly attenuated by HBO therapy. The TBI-induced local and systemic TNF-α expression, neuronal damage score, and neuronal apoptosis were also significantly reduced by HBO therapy. Moreover, HBO treatment attenuated the expression of TGIF but increased TGF-β1 expression in neurons.

CONCLUSIONS

We concluded that treatment of TBI with HBO during the acute phase of injury can decrease local and systemic proinflammatory cytokine TNF-α production, resulting in neuroprotective effects. We also suggest that decreased levels of TGIF and increased levels of TGF-β in the injured cortex leading to decreased neuronal apoptosis is one mechanism by which functional recovery may occur.

Incomplete Assessment of Experimental Cytoprotectants in Rodent Ischemia Studies

Background:

Inadequate preclinical testing (e.g., rodent studies) has been partly blamed for the failure of many cytoprotectants to effectively treat stroke in humans. For example, some drugs went to clinical trial without rigorous functional and histological assessment over long survival times. In this study, we characterized recent experimental practices in rodent cytoprotection experiments to determine whether the limitations of early studies have been rectified.

Methods:

We identified 138 rodent cytoprotection studies published in several leading journals (Journal of Neuroscience, Stroke, Journal of Cerebral Blood Flow and Metabolism and Experimental Neurology) for 2000 - 2002 and compared these to those published in 1990. From each study we determined the ischemia model, age and sex of the animal, the histological and functional endpoints used, and the methodology used to assess intra- and postischemic temperature.

Results:

Ninety-eight percent of recent studies used young adult rodents and most used males. Most studies (60%) did not assess functional outcome and survival times were often ≤ 48 hr (66%) for focal ischemia and ≤ 7 days (80%) for global ischemia. Over 60% of the experiments relied solely upon rectal temperature during ischemia and only 32.6% of ischemia studies measured temperature after surgery. The 1990 data were similar.

Conclusion:

Many investigators ignore the need to assess long-term functional and histological outcome and do not accurately represent clinical conditions of ischemia (e.g., use of aged animals). In addition, intra- and postischemic temperature measurement and control is frequently neglected or inadequately performed. Further clinical failures are likely.

Hydrogen inhalation during normoxic resuscitation improves neurological outcome in a rat model of cardiac arrest independently of targeted temperature management

BACKGROUND

We have previously shown that hydrogen (H2) inhalation, begun at the start of hyperoxic cardiopulmonary resuscitation, significantly improves brain and cardiac function in a rat model of cardiac arrest. Here, we examine the effectiveness of this therapeutic approach when H2 inhalation is begun on the return of spontaneous circulation (ROSC) under normoxic conditions, either alone or in combination with targeted temperature management (TTM).

METHODS AND RESULTS

Rats were subjected to 6 minutes of ventricular fibrillation cardiac arrest followed by cardiopulmonary resuscitation. Five minutes after achieving ROSC, post-cardiac arrest rats were randomized into 4 groups: mechanically ventilated with 26% O2 and normothermia (control); mechanically ventilated with 26% O2, 1.3% H2, and normothermia (H2); mechanically ventilated with 26% O2 and TTM (TTM); and mechanically ventilated with 26% O2, 1.3% H2, and TTM (TTM+H2). Animal survival rate at 7 days after ROSC was 38.4% in the control group, 71.4% in the H2 and TTM groups, and 85.7% in the TTM+H2 group. Combined therapy of TTM and H2 inhalation was superior to TTM alone in terms of neurological deficit scores at 24, 48, and 72 hours after ROSC, and motor activity at 7 days after ROSC. Neuronal degeneration and microglial activation in a vulnerable brain region was suppressed by both TTM alone and H2 inhalation alone, with the combined therapy of TTM and H2 inhalation being most effective.

CONCLUSIONS

H2 inhalation was beneficial when begun after ROSC, even when delivered in the absence of hyperoxia. Combined TTM and H2 inhalation was more effective than TTM alone.

Effects of levosimendan on hemodynamics, local cerebral blood flow, neuronal injury, and neuroinflammation after asphyctic cardiac arrest in rats

OBJECTIVES

Despite advances in cardiac arrest treatment, high mortality and morbidity rates after successful cardiopulmonary resuscitation are still a major clinical relevant problem. The post cardiac arrest syndrome subsumes myocardial dysfunction, impaired microcirculation, systemic inflammatory response, and neurological impairment. The calcium-sensitizer levosimendan was able to improve myocardial function and initial resuscitation success after experimental cardiac arrest/cardiopulmonary resuscitation. We hypothesized that levosimendan exerts beneficial effects on cerebral blood flow, neuronal injury, neurological outcome, and inflammation 24 hours after experimental cardiac arrest/cardiopulmonary resuscitation.

DESIGN

Laboratory animal study.

SETTING

University animal research laboratory.

SUBJECTS

Sixty-one male Sprague-Dawley rats.

INTERVENTIONS

Animals underwent asphyxial cardiac arrest/cardiopulmonary resuscitation, randomized to groups with levosimendan treatment (bolus 12 µg/kg and infusion for 3 hr [0.3 µg/min/kg]) or vehicle (saline 0.9% bolus and infusion for 3 hr [equivalent fluid volume]). Cardiac index, local cerebral blood flow, and hemodynamic variables were measured for 180 minutes after cardiac arrest/cardiopulmonary resuscitation. Behavioral and neurological evaluations were conducted 24 hours after cardiac arrest/cardiopulmonary resuscitation. Furthermore, neuronal injury, expressed as Fluoro-Jade B-positive cells in the hippocampal formation, cortical and hippocampal inflammatory cytokine gene expression, and blood plasma interleukin-6 values were assessed.

MEASUREMENTS AND MAIN RESULTS

Treatment with levosimendan reduced neuronal injury and improved neurological outcome after 24 hours of reperfusion and resulted in elevated cardiac index and local cerebral blood flow compared with vehicle after cardiac arrest/cardiopulmonary resuscitation. Mean arterial blood pressure was reduced during the early reperfusion period in the levosimendan group. Cortical and hippocampal inflammatory cytokine gene expression and blood plasma interleukin-6 levels were not influenced.

CONCLUSIONS

Levosimendan increased cerebral blood flow after experimental cardiac arrest/cardiopulmonary resuscitation. This effect coincided with reduced neuronal injury and improved neurologic outcome. Findings seem to be independent of inflammatory effects because no effects by levosimendan on cerebral or systemic inflammation could be detected. In summary, levosimendan is a promising agent to improve neurological outcome after cardiac arrest/cardiopulmonary resuscitation.

Global and regional differences in cerebral blood flow after asphyxial versus ventricular fibrillation cardiac arrest in rats using ASL-MRI

Both ventricular fibrillation cardiac arrest (VFCA) and asphyxial cardiac arrest (ACA) are frequent causes of CA. However, only isolated reports compared cerebral blood flow (CBF) reperfusion patterns after different types of CA, and even fewer reports used methods that allow serial and regional assessment of CBF. We hypothesized that the reperfusion patterns of CBF will differ between individual types of experimental CA. In a prospective block-randomized study, fentanyl-anesthetized adult rats were subjected to 8min VFCA or ACA. Rats were then resuscitated with epinephrine, bicarbonate, manual chest compressions and mechanical ventilation. After the return of spontaneous circulation, CBF was then serially assessed via arterial spin-labeling magnetic resonance imaging (ASL-MRI) in cortex, thalamus, hippocampus and amygdala/piriform complex over 1h resuscitation time (RT). Both ACA and VFCA produced significant temporal and regional differences in CBF. All regions in both models showed significant changes over time (p<0.01), with early hyperperfusion and delayed hypoperfusion. ACA resulted in early hyperperfusion in cortex and thalamus (both p<0.05 vs. amygdala/piriform complex). In contrast, VFCA induced early hyperperfusion only in cortex (p<0.05 vs. other regions). Hyperperfusion was prolonged after ACA, peaking at 7min RT (RT7; 199% vs. BL, Baseline, in cortex and 201% in thalamus, p<0.05), then returning close to BL at ∼RT15. In contrast, VFCA model induced mild hyperemia, peaking at RT7 (141% vs. BL in cortex). Both ACA and VFCA showed delayed hypoperfusion (ACA, ∼30% below BL in hippocampus and amygdala/piriform complex, p<0.05; VFCA, 34-41% below BL in hippocampus and amygdala/piriform complex, p<0.05). In conclusion, both ACA and VFCA in adult rats produced significant regional and temporal differences in CBF. In ACA, hyperperfusion was most pronounced in cortex and thalamus. In VFCA, the changes were more modest, with hyperperfusion seen only in cortex. Both insults resulted in delayed hypoperfusion in all regions. Both early hyperperfusion and delayed hypoperfusion may be important therapeutic targets. This study was approved by the University of Pittsburgh IACUC 1008816-1.

Fatty acid methyl esters and Solutol HS 15 confer neuroprotection after focal and global cerebral ischemia

We previously showed that palmitic acid methyl ester (PAME) and stearic acid methyl ester (SAME) are simultaneously released from the sympathetic ganglion and PAME possesses potent vasodilatory properties which may be important in cerebral ischemia. Since PAME is a potent vasodilator simultaneously released with SAME, our hypothesis was that PAME/SAME confers neuroprotection in rat models of focal/global cerebral ischemia. We also examined the neuroprotective properties of Solutol HS15, a clinically approved excipient because it possesses similar fatty acid compositions as PAME/SAME. Asphyxial cardiac arrest (ACA, 6 min) was performed 30 min after PAME/SAME treatment (0.02 mg/kg, IV). Solutol HS15 (2 ml/kg, IP) was injected chronically for 14 days (once daily). Histopathology of hippocampal CA1 neurons was assessed 7 days after ACA. For focal ischemia experiments, PAME, SAME, or Solutol HS15 was administered following reperfusion after 2 h of middle cerebral artery occlusion (MCAO). 2,3,5-Triphenyltetrazolium staining of the brain was performed 24 h after MCAO and the infarct volume was quantified. Following ACA, the number of surviving hippocampal neurons was enhanced by PAME-treated (68%), SAME-treated (69%), and Solutol-treated HS15 (68%) rats as compared to ACA only-treated groups. Infarct volume was decreased by PAME (83%), SAME (68%), and Solutol HS15 (78%) as compared to saline (vehicle) in MCAO-treated animals. PAME, SAME, and Solutol HS15 provide robust neuroprotection in both paradigms of ischemia. This may prove therapeutically beneficial since Solutol HS15 is already administered as a solublizing agent to patients. With proper timing and dosage, administration of Solutol HS15 and PAME/SAME can be an effective therapy against cerebral ischemia.

Brain resuscitation in the drowning victim

Drowning is a leading cause of accidental death. Survivors may sustain severe neurologic morbidity. There is negligible research specific to brain injury in drowning making current clinical management non-specific to this disorder. This review represents an evidence-based consensus effort to provide recommendations for management and investigation of the drowning victim. Epidemiology, brain-oriented prehospital and intensive care, therapeutic hypothermia, neuroimaging/monitoring, biomarkers, and neuroresuscitative pharmacology are addressed. When cardiac arrest is present, chest compressions with rescue breathing are recommended due to the asphyxial insult. In the comatose patient with restoration of spontaneous circulation, hypoxemia and hyperoxemia should be avoided, hyperthermia treated, and induced hypothermia (32-34 °C) considered. Arterial hypotension/hypertension should be recognized and treated. Prevent hypoglycemia and treat hyperglycemia. Treat clinical seizures and consider treating non-convulsive status epilepticus. Serial neurologic examinations should be provided. Brain imaging and serial biomarker measurement may aid prognostication. Continuous electroencephalography and N20 somatosensory evoked potential monitoring may be considered. Serial biomarker measurement (e.g., neuron specific enolase) may aid prognostication. There is insufficient evidence to recommend use of any specific brain-oriented neuroresuscitative pharmacologic therapy other than that required to restore and maintain normal physiology. Following initial stabilization, victims should be transferred to centers with expertise in age-specific post-resuscitation neurocritical care. Care should be documented, reviewed, and quality improvement assessment performed. Preclinical research should focus on models of asphyxial cardiac arrest. Clinical research should focus on improved cardiopulmonary resuscitation, re-oxygenation/reperfusion strategies, therapeutic hypothermia, neuroprotection, neurorehabilitation, and consideration of drowning in advances made in treatment of other central nervous system disorders.

H(2) gas improves functional outcome after cardiac arrest to an extent comparable to therapeutic hypothermia in a rat model

Background

All clinical and biological manifestations related to postcardiac arrest (CA) syndrome are attributed to ischemia–reperfusion injury in various organs including brain and heart. Molecular hydrogen (H₂) has potential as a novel antioxidant. This study tested the hypothesis that inhalation of H₂ gas starting at the beginning of cardiopulmonary resuscitation (CPR) could improve the outcome of CA.

Methods and Results

Ventricular fibrillation was induced by transcutaneous electrical epicardial stimulation in rats. After 5 minutes of the subsequent CA, rats were randomly assigned to 1 of 4 experimental groups at the beginning of CPR: mechanical ventilation (MV) with 2% N₂ and 98% O₂ under normothermia (37°C), the control group; MV with 2% H₂ and 98% O₂ under normothermia; MV with 2% N₂ and 98% O₂ under therapeutic hypothermia (TH), 33°C; and MV with 2% H₂ and 98% O₂ under TH. Mixed gas inhalation and TH continued until 2 hours after the return of spontaneous circulation (ROSC). H₂ gas inhalation yielded better improvement in survival and neurological deficit score (NDS) after ROSC to an extent comparable to TH. H₂ gas inhalation, but not TH, prevented a rise in left ventricular end-diastolic pressure and increase in serum IL-6 level after ROSC. The salutary impact of H₂ gas was at least partially attributed to the radical-scavenging effects of H₂ gas, because both 8-OHdG- and 4-HNE-positive cardiomyocytes were markedly suppressed by H₂ gas inhalation after ROSC.

Conclusions

Inhalation of H₂ gas is a favorable strategy to mitigate mortality and functional outcome of post-CA syndrome in a rat model, either alone or in combination with TH.

Cannabinoid 1 (CB1) receptor mediates WIN55, 212-2 induced hypothermia and improved survival in a rat post-cardiac arrest model

AIM

The nonselective Cannabinoid (CB) receptor agonist, WIN55, 212-2, was demonstrated to induce hypothermia and improve post-resuscitation outcomes in a rat post-cardiac arrest model. The present study was to explore the potential mechanisms of WIN55, 212-2 on thermoregulation following resuscitation and to investigate which class of CB receptors was involved in WIN55, 212-2-induced hypothermia.

METHODS

Ventricular fibrillation (VF) was induced and untreated for 6 min in 20 male Sprague-Dawley rats. Defibrillation was attempted after 8min of Cardiopulmonary resuscitation (CPR). Five min post-resuscitation, resuscitated animals were randomized to receive an intramuscular injection of selective CB1 receptors antagonist, SR141716A (5 mg kg(-1)); selective CB2 receptors antagonist SR144528 (5 mg kg(-1)); or placebo. Thirty min after injection, animals received continuous intravenous infusion of WIN55, 212-2 (1.0 mgkg(-1) h(-1)) for 4h while control animals received placebo. The identical temperature environment was maintained in all animals.

RESULTS

In animals treated with WIN55, 212-2, blood temperatures decreased progressively from 37 °C to 34 °C within 4h. This hypothermic effect was completely blocked by CB1 but not CB2 antagonist. Accordingly, significantly better cardiac output, ejection fraction and myocardial performance index, reduced neurological deficit scores, improved microcirculation and longer duration of survival were observed in WIN55, 212-2-treated animals, which were also completely abolished by pretreatment with CB1 antagonist.

CONCLUSIONS

Pharmacologically induced hypothermia with WIN55, 212-2 improved post-resuscitation myocardial and cerebral function, associated with a significantly increased duration of survival in a rat post-cardiac arrest model. The hypothermic and resulted beneficial effects of WIN55, 212-2 were mediated through CB1 receptors.

Cholecystokinin octapeptide induces hypothermia and improves outcomes in a rat model of cardiopulmonary resuscitation

OBJECTIVES

To investigate the effects of cholecystokinin octapeptide on thermoregulation, postresuscitation myocardial function, neurologic outcome, and duration of survival in a rat model of cardiopulmonary resuscitation.

DESIGN

: Prospective, randomized, placebo-controlled experimental study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Ten male Sprague-Dawley rats.

INTERVENTIONS

Ventricular fibrillation was induced and untreated for 6 mins. Defibrillation was attempted after 8 mins of cardiopulmonary resuscitation. Animal temperature was adjusted to 37.0 °C with the aid of a heating lamp. At 30 mins after resuscitation, animals were randomized to receive an intravenous injection of either cholecystokinin octapeptide (200 μg/kg in 0.3 mL saline) or vehicle placebo (0.3 mL saline). The ambient temperature settings and that of the distance of the heating lamp from the animal remained the same in both groups throughout the entire experiment.

MEASUREMENTS AND MAIN RESULTS

Body temperature, hemodynamic measurements, and postresuscitation myocardial function, including cardiac output, left ventricular ejection fraction, and myocardial performance index, were measured together with neurologic deficit scores and duration of survival.

RESULTS

After injection of cholecystokinin octapeptide, blood temperature decreased progressively from 37.0 °C to 34.8 °C 5 hrs after resuscitation and returned to 37.0 °C at 9 hrs after injection. In the control group, blood temperature was sustained at 37.0 °C ± 0.2 °C during the same period of observation. Myocardial and neurologic function and duration of survival were significantly better in the cholecystokinin octapeptide-treated animals when compared to the control group.

CONCLUSIONS

: In a rat model of cardiopulmonary resuscitation, cholecystokinin octapeptide induced mild hypothermia, attenuated postresuscitation myocardial dysfunction, and improved neurologic outcome and duration of survival.

Hypothermia and pediatric cardiac arrest

The survival outcome following pediatric cardiac arrest still remains poor. Survival to hospital discharge ranges anywhere from 0 to 38% when considering both out-of-hospital and in-hospital arrests, with up to 50% of the survivors having neurologic injury. The use of mild induced hypothermia has not been definitively proven to improve outcomes following pediatric cardiac arrest. This may be due to the lack of consensus regarding target temperature, best method of cooling, optimal duration of cooling and identifying the patient population who will receive the greatest benefit. We review the current applications of induced hypothermia in pediatric patients following cardiac arrest after searching the current literature through Pubmed and Ovid journal databases. We put forth compiled recommendations/guidelines for initiating hypothermia therapy, its maintenance, associated monitoring and suggested adjunctive therapies to produce favorable neurologic and survival outcomes.

Mild hypothermia delays the development of stone heart from untreated sustained ventricular fibrillation--a cardiovascular magnetic resonance study

BACKGROUND

'Stone heart' resulting from ischemic contracture of the myocardium, precludes successful resuscitation from ventricular fibrillation (VF). We hypothesized that mild hypothermia might slow the progression to stone heart.

METHODS

Fourteen swine (27 ± 1 kg) were randomized to normothermia (group I; n=6) or hypothermia groups (group II; n=8). Mild hypothermia (34 ± 2 °C) was induced with ice packs prior to VF induction. The LV and right ventricular (RV) cross-sectional areas were followed by cardiovascular magnetic resonance until the development of stone heart. A commercial 1.5T GE Signa NV-CV/i scanner was used. Complete anatomic coverage of the heart was acquired using a steady-state free precession (SSFP) pulse sequence gated at baseline prior to VF onset. Un-gated SSFP images were obtained serially after VF induction. The ventricular endocardium was manually traced and LV and RV volumes were calculated at each time point.

RESULTS

In group I, the LV was dilated compared to baseline at 5 minutes after VF and this remained for 20 minutes. Stone heart, arbitrarily defined as LV volume <1/3 of baseline at the onset of VF, occurred at 29 ± 3 minutes. In group II, there was less early dilation of the LV (p<0.05) and the development of stone heart was delayed to 52 ± 4 minutes after onset of VF (P<0.001).

CONCLUSIONS

In this closed-chest swine model of prolonged untreated VF, hypothermia reduced the early LV dilatation and importantly, delayed the onset of stone heart thereby extending a known, morphologic limit of resuscitability.

How I cool children in neurocritical care

Brain injury is the leading cause of death in our pediatric ICU [Au et al. Crit Care Med 36:A128, 2008]. Clinical care for brain injury remains largely supportive. Therapeutic hypothermia has been shown to be effective in improving neurological outcome after adult ventricular-arrhythmia-induced cardiac arrest and neonatal asphyxia, and is under investigation as a neuroprotectant after cardiac arrest and traumatic brain injury in children in our ICU and other centers. To induce hypothermia in children comatose after cardiac arrest we target 32-34 degrees C using cooling blankets and intravenous iced saline as primary methods for induction, for 24-72 h duration with vigilant re-warming. The objective of this article is to share our hypothermia protocol for cooling children with acute brain injury.

Application of Induced Hypothermia for Neuroprotection after Cardiac Arrest: A Systematic Review

The dismal outcome after cardiac arrest calls for novel therapeutic approaches. Therapeutic hypothermia is a promising therapeutic modality. In this article we review the evidence for therapeutic hypothermia, for the best methods for cooling available and for the safety of therapeutic hypothermia.

Use of prolonged hypothermia to treat ischemic and hemorrhagic stroke

Therapeutic (induced) hypothermia (TH) has been extensively studied as a means to reduce brain injury following global and focal cerebral ischemia, intracerebral hemorrhage (ICH), and subarachnoid hemorrhage (SAH). Here, we briefly review the clinical and experimental evidence supporting the use of TH in each condition. We emphasize the importance of systematically evaluating treatment parameters, especially the duration of cooling, in each condition. We contend that TH provides considerable protection after global and focal cerebral ischemia, especially when cooling is prolonged (e.g., >24 h). However, there is presently insufficient evidence to support the clinical use of TH for ICH and SAH. In any case, further animal work is needed to develop optimized protocols for treating cardiac arrest (global ischemia), and to maximize the likelihood of successful clinical translation in focal cerebral ischemia.

Mechanisms of action, physiological effects, and complications of hypothermia

BACKGROUND

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

OBJECTIVE

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

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

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

CONCLUSIONS

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

Acute brain injury and therapeutic hypothermia in the PICU: A rehabilitation perspective

Acquired brain injury from traumatic brain injury, cardiac arrest (CA), stroke, and central nervous system infection is a leading cause of morbidity and mortality in the pediatric population and reason for admission to inpatient rehabilitation. Therapeutic hypothermia is the only intervention shown to have efficacy from bench to bedside in improving neurological outcome after birth asphyxia and adult arrhythmia-induced CA, thought to be due to its multiple mechanisms of action. Research to determine if therapeutic hypothermia should be applied to other causes of brain injury and how to best apply it is underway in children and adults. Changes in clinical practice in the hospitalized brain-injured child may have effects on rehabilitation referral practices, goals and strategies of therapies offered, and may increase the degree of complex medical problems seen in children referred to inpatient rehabilitation.

Current and future therapies of pediatric cardiopulmonary arrest

OBJECTIVE

To review contemporary guidelines and therapies for pediatric cardiac arrest and discuss potential novel therapies.

METHODS

Key articles and guidelines in the field were reviewed along with recent publications in the fields of neurointensive care and neuroscience germane to cerebral resuscitation.

RESULTS

A total of 45 articles were reviewed. The majority of arrests in the pediatric population are asphyxial in origin--which differs importantly from the adult population. The International Consensus on CPR guidelines are discussed, including good quality CPR, chest compressions without interruptions, resuscitation with 100% oxygen and subsequent titration of oxygen to normal oxygen saturations, correct dose of epinephrine, and use of hypothermia in the first 12-24 hours. Novel therapies that showed success in animal studies, such as hypertensive reperfusion, thrombolytics, hemodilution and extracorporeal CPR are also discussed.

CONCLUSION

With only 30% return of spontaneous circulation, 12% survival to hospital discharge and 4% intact neurologic survival, pediatric cardiac arrest remains an area of intense research for therapies to improve its outcomes. In addition to the rapid implementation of basic and advanced life support interventions, new therapies that may have value include mild hypothermia, extracorporeal support, promotion of cerebral blood flow and other more novel therapies targeting oxidative stress, excitotoxicity, neuronal death, and rehabilitation.