Beneficial Effects Of Therapeutic Hypothermia Research Articles

The Effect of Therapeutic Hypothermia on Ischemic Brain Injury in a Rat Model of Cardiac Arrest: An Assessment Using 18F-FDG PET.

Therapeutic hypothermia (TH) is widely acknowledged as one of the interventions for preventing hypoxic ischemic brain injury in comatose patients following cardiac arrest (CA). Despite its recognized efficacy, recent debates have questioned its effectiveness. This preclinical study evaluated the impact of TH on brain glucose metabolism, utilizing fluorine-18-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) in a rat model of CA. Asphyxia CA was induced in Sprague-Dawley rats using vecuronium. Brain PET images using 18F-FDG were obtained from 21 CA rats, who were randomized to receive either TH or no intervention. Of these, 9 rats in the TH group received hypothermia under general anesthesia and mechanical ventilation for eight hours, while the remaining 12 rats in the non-TH group were observed without intervention. We conducted regional and voxel-based analyses of standardized uptake values relative to the pons (SUVRpons) to compare the two groups. Survival rates were identical in both the TH and non-TH groups (67%). There was no discernible difference in the SUVRpons across the brain cortical regions between the groups. However, in a subgroup analysis of the rats that did not survive (n = 7), those in the TH group (n = 3) displayed significantly higher SUVRpons values across most cortical regions compared to those in the non-TH group (n = 4), with statistical significance after false-discovery rate correction (p < 0.05). The enhancement in SUVRpons due to TH intervention was only observed in the cortical regions of rats with severe encephalopathy that subsequently died. These findings suggest that the beneficial effects of TH on brain glucose metabolism in this asphyxia CA model may be confined to cases of severe ischemic encephalopathy.

Differential Effects of Hypothermia and SZR72 on Cerebral Kynurenine and Kynurenic Acid in a Piglet Model of Hypoxic-Ischemic Encephalopathy.

Kynurenic acid (KYNA), an endogenous neuroprotectant with antiexcitotoxic, antioxidant, and anti-inflammatory effects, is synthesized through the tryptophan-kynurenine (KYN) pathway. We investigated whether brain KYN or KYNA levels were affected by asphyxia in a translational piglet model of hypoxic-ischemic encephalopathy (HIE). We also studied brain levels of the putative blood-brain barrier (BBB) permeable neuroprotective KYNA analogue SZR72, and whether SZR72 or therapeutic hypothermia (TH) modified KYN or KYNA levels. KYN, KYNA, and SZR72 levels were determined using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry in five brain regions 24 h after 20 min of asphyxia in vehicle-, SZR72- and TH-treated newborn piglets (n = 6-6-6) and naive controls (n = 4). Endogenous brain KYN levels (median range 311.2-965.6 pmol/g) exceeded KYNA concentrations (4.5-6.0 pmol/g) ~100-fold. Asphyxia significantly increased cerebral KYN and KYNA levels in all regions (1512.0-3273.9 and 16.9-21.2 pmol/g, respectively), increasing the KYN/Tryptophan-, but retaining the KYNA/KYN ratio. SZR72 treatment resulted in very high cerebral SZR72 levels (13.2-33.2 nmol/g); however, KYN and KYNA levels remained similar to those of the vehicle-treated animals. However, TH virtually ameliorated asphyxia-induced elevations in brain KYN and KYNA levels. The present study reports for the first time that the KYN pathway is altered during HIE development in the piglet. SZR72 readily crosses the BBB in piglets but fails to affect cerebral KYNA levels. Beneficial effects of TH may include restoration of the tryptophan metabolism to pre-asphyxia levels.

Cerebrospinal fluid is a significant fluid source for anoxic cerebral oedema.

Cerebral oedema develops after anoxic brain injury. In two models of asphyxial and asystolic cardiac arrest without resuscitation, we found that oedema develops shortly after anoxia secondary to terminal depolarizations and the abnormal entry of CSF. Oedema severity correlated with the availability of CSF with the age-dependent increase in CSF volume worsening the severity of oedema. Oedema was identified primarily in brain regions bordering CSF compartments in mice and humans. The degree of ex vivo tissue swelling was predicted by an osmotic model suggesting that anoxic brain tissue possesses a high intrinsic osmotic potential. This osmotic process was temperature-dependent, proposing an additional mechanism for the beneficial effect of therapeutic hypothermia. These observations show that CSF is a primary source of oedema fluid in anoxic brain. This novel insight offers a mechanistic basis for the future development of alternative strategies to prevent cerebral oedema formation after cardiac arrest.

POLAR Study Revisited: Therapeutic Hypothermia in Severe Brain Trauma Should Not Be Abandoned.

The benefits of therapeutic hypothermia (TH) in severe traumatic brain injury (sTBI) have been long debated. In 2018, the POLAR study, a high-quality international trial, appeared to end the debate by showing that TH did not improve mortality in sTBI. However, the POLAR-based recommendation to abandon TH was challenged by different investigators. In our recent meta-analysis, we introduced the cooling index (COIN) to assess the extent of cooling and showed that TH is beneficial in sTBI, but only when the COIN is sufficiently high. In the present study, we calculated the COIN for the POLAR study and ran a new meta-analysis, which included the POLAR data and accounted for the cooling extent. The POLAR study targeted a high cooling extent (COIN of 276°C × h; calculated for 72 h), but the achieved cooling was much lower (COIN of 193°C × h)-because of deviations from the protocol. When the POLAR data were included in the COIN-based meta-analysis, TH had an overall effect of reducing death (odds rate of 0.686; p = 0.007). Among the subgroups with different COIN levels, the only significantly decreased odds rate (i.e., beneficial effect of TH) was observed in the subgroup with high COIN (0.470; p = 0.013). We conclude that, because of deviations from the targeted cooling protocol, the overall cooling extent was not sufficiently high in the POLAR study, thus masking the beneficial effects of TH. The current analysis shows that TH is beneficial in sTBI, but only when the COIN is high. Abandoning the use of TH in sTBI may be premature.

Effect of Amiodarone and Hypothermia on Arrhythmia Substrates During Resuscitation.

BackgroundAmiodarone is administered during resuscitation, but its antiarrhythmic effects during targeted temperature management are unknown. The purpose of this study was to determine the effect of both therapeutic hypothermia and amiodarone on arrhythmia substrates during resuscitation from cardiac arrest.Methods and ResultsWe utilized 2 complementary models: (1) In vitro no‐flow global ischemia canine left ventricular transmural wedge preparation. Wedges at different temperatures (36°C or 32°C) were given 5 µmol/L amiodarone (36‐Amio or 32‐Amio, each n=8) and subsequently underwent ischemia and reperfusion. Results were compared with previous controls. Optical mapping was used to measure action potential duration, dispersion of repolarization (DOR), and conduction velocity (CV). (2) In vivo pig model of resuscitation. Pigs (control or targeted temperature management, 32–34°C) underwent ischemic cardiac arrest and were administered amiodarone (or not) after 8 minutes of ventricular fibrillation. In vitro: therapeutic hypothermia but not amiodarone prolonged action potential duration. During ischemia, DOR increased in the 32‐Amio group versus 32‐Alone (84±7 ms versus 40±7 ms, P<0.05) while CV slowed in the 32‐Amio group. Amiodarone did not affect CV, DOR, or action potential duration during ischemia at 36°C. Conduction block was only observed at 36°C (5/8 36‐Amio versus 6/7 36‐Alone, 0/8 32‐Amio, versus 0/7 32‐Alone). In vivo: QTc decreased upon reperfusion from ischemia that was ameliorated by targeted temperature management. Amiodarone did not worsen DOR or CV. Amiodarone suppressed rearrest caused by ventricular fibrillation (7/8 without amiodarone, 2/7 with amiodarone, P=0.041), but not pulseless electrical activity (2/8 without amiodarone, 5/7 with amiodarone, P=0.13).ConclusionsAlthough amiodarone abolishes a beneficial effect of therapeutic hypothermia on ischemia‐induced DOR and CV, it did not worsen susceptibility to ventricular tachycardia/ventricular fibrillation during resuscitation.

Impact of neonatal anoxia and hypothermic treatment on development and memory of rats

Therapeutic hypothermia (TH) is well established as a standard treatment for term and near-term infants. However, therapeutic effects of hypothermia following neonatal anoxia in very premature babies remains inconclusive. The present rodent model of preterm neonatal anoxia has been shown to alter developmental milestones and hippocampal neurogenesis, and to disrupt spatial learning and memory in adulthood. These effects seem to be reduced by post-insult hypothermia. Epigenetic-related mechanisms have been postulated as valuable tools for developing new therapies. Dentate gyrus neurogenesis is regulated by epigenetic factors. This study evaluated whether TH effects in a rodent model of preterm oxygen deprivation are based on epigenetic alterations. The effects of TH on both developmental features (somatic growth, maturation of physical characteristics and early neurological reflexes) and performance of behavioral tasks at adulthood (spatial reference and working memory, and fear conditioning) were investigated in association with the possible involvement of the epigenetic operator Enhancer of zeste homolog 2 (Ezh2), possibly related to long-lasting effects on hippocampal neurogenesis. Results showed that TH reduced both anoxia-induced hippocampal neurodegeneration and anoxia-induced impairments on risk assessment behavior, acquisition of spatial memory, and extinction of auditory and contextual fear conditioning. In contrast, TH did not prevent developmental alterations caused by neonatal anoxia and did not restore hippocampal neurogenesis or cause changes in EZH2 levels. In conclusion, despite the beneficial effects of TH in hippocampal neurodegeneration and in reversing disruption of performance of behavioral tasks following oxygen deprivation in prematurity, these effects seem not related to developmental alterations and hippocampal neurogenesis and, apparently, is not caused by Ezh2-mediated epigenetic alteration.

Temperature Variability Does Not Attenuate the Beneficial Effects of Therapeutic Hypothermia on Cellular Apoptosis and Endoplasmic Reticulum Stress in the Cerebral Cortex of a Swine Cardiac Arrest Model.

Endoplasmic reticulum stress (ERS) plays a vital role in mediating apoptosis in the brain following cardiac arrest (CA). Studies have shown that therapeutic hypothermia (TH) provides neuroprotection through anti-apoptosis; however, the effects of temperature variability in TH on the brain remain unclear. In this study, we investigated the different effects of temperature variability through extracorporeal membrane oxygenation on apoptosis and ERS in the brain following CA. Eighteen male domestic pigs underwent 6-min duration of no-flow induced by ventricular fibrillation. Extracorporeal cardiopulmonary resuscitation was then performed, and the return of spontaneous circulation (ROSC) was achieved. The animals were randomly assigned to the following groups: normothermia, non-temperature variability, and temperature variability. TH (core temperature, 33-35°C) was maintained for 24h post-ROSC, and the animals were rewarmed for 8h. Quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry for Bax and Bcl-2 transcripts and proteins, respectively, were used to investigate apoptosis in the cerebral cortex. Expression levels of the ERS molecules, GRP78 and CHOP, were also detected by qRT-PCR, and cellular morphology was evaluated using transmission electron microscopy. qRT-PCR and immunohistochemistry results revealed that TH significantly increased the expression levels of Bcl-2 and GRP78 and decreased that of Bax and CHOP than under normothermia conditions. Compared to the non-temperature variability group, temperature variability did not decrease the expression levels of Bcl-2 and GRP78 and not increase the levels of Bax and CHOP. Endoplasmic reticulum ultrastructural changes were significantly improved under TH. No statistical difference was observed between the temperature variability andnon-temperature variabilitygroups. TH can reduce neuronal apoptosis by ERS, while temperature variability does not attenuate this beneficial effect.

Therapeutic Hypothermia in Acute Ischemic Stroke-a Systematic Review and Meta-Analysis.

Therapeutic hypothermia (TH) in stroke demonstrates robust neuroprotection in animals but clinical applications remain controversial. We assessed current literature on the efficacy of TH in ischemic stroke. We conducted a meta-analysis comparing TH versus controls in studies published until June 2019. Controlled studies reporting on ≥ 10 adults with acute ischemic stroke were included. Primary outcome was functional independence (modified Rankin Scale [mRS] ≤ 2). Twelve studies (n = 351 TH, n = 427 controls) were included. Functional independence did not differ between groups (RR 1.17, 95% CI 0.93-1.46, random-effects p = 0.2). Five studies reported individual mRS outcomes and demonstrated a shift toward better outcome with TH (unadjusted cOR 1.57, 95% CI 1.01-2.44, p = 0.05). Overall complications were higher with TH (RR 1.18, 95% CI 1.06-1.32, p < 0.01). We did not observe an overall beneficial effect of TH in this analysis although some studies showed a shift toward better outcome. TH was associated with increased complications.

The Beneficial Effect of Therapeutic Hypothermia to Improve the Survival of Patients with Out-of-Hospital Cardiac Arrest.

The Beneficial Effect of Therapeutic Hypothermia to Improve the Survival of Patients with Out-of-Hospital Cardiac Arrest.

Myocardial hypothermia increases autophagic flux, mitochondrial mass and myocardial function after ischemia-reperfusion injury

Animal studies have demonstrated beneficial effects of therapeutic hypothermia on myocardial function, yet exact mechanisms remain unclear. Impaired autophagy leads to heart failure and mitophagy is important for mitigating ischemia/reperfusion injury. This study aims to investigate whether the beneficial effects of therapeutic hypothermia are due to preserved autophagy and mitophagy. Under general anesthesia, the left anterior descending coronary artery of 19 female farm pigs was occluded for 90 minutes with consecutive reperfusion. 30 minutes after reperfusion, we performed pericardial irrigation with warm or cold saline for 60 minutes. Myocardial tissue analysis was performed one and four weeks after infarction. Therapeutic hypothermia induced a significant increase in autophagic flux, mitophagy, mitochondrial mass and function in the myocardium after infarction. Cell stress, apoptosis, inflammation as well as fibrosis were reduced, with significant preservation of systolic and diastolic function four weeks post infarction. We found similar biochemical changes in human samples undergoing open chest surgery under hypothermic conditions when compared to the warm. These results suggest that autophagic flux and mitophagy are important mechanisms implicated in cardiomyocyte recovery after myocardial infarction under hypothermic conditions. New therapeutic strategies targeting these pathways directly could lead to improvements in prevention of heart failure.

Neuroprotection by Therapeutic Hypothermia.

Hypothermia therapy is an old and important method of neuroprotection. Until now, many neurological diseases such as stroke, traumatic brain injury, intracranial pressure elevation, subarachnoid hemorrhage, spinal cord injury, hepatic encephalopathy, and neonatal peripartum encephalopathy have proven to be suppressed by therapeutic hypothermia. Beneficial effects of therapeutic hypothermia have also been discovered, and progress has been made toward improving the benefits of therapeutic hypothermia further through combination with other neuroprotective treatments and by probing the mechanism of hypothermia neuroprotection. In this review, we compare different hypothermia induction methods and provide a summarized account of the synergistic effect of hypothermia therapy with other neuroprotective treatments, along with an overview of hypothermia neuroprotection mechanisms and cold/hypothermia-induced proteins.

Magnesium Levels and Neurologic Outcomes in Patients Undergoing Therapeutic Hypothermia After Cardiac Arrest.

Therapeutic hypothermia (TH) improves neurological outcomes after cardiac arrest by mitigating cerebral reperfusion injury. Serum magnesium (Mg) inhibits glutamate release, restores blood-brain barrier integrity, and decreases brain edema. The neuroprotective role of Mg in cardiac arrest patients undergoing TH is not well established. We analyzed 438 survivors of cardiac arrest who completed a TH protocol from 2008 through 2016. Multivariate and receiver operating characteristic (ROC) analyses examined the association between Mg supplementation and Mg levels before, during, and after TH with neurologic outcomes. Participants were 65.5 ± 15.9 years old, 47% received bystander cardiopulmonary resuscitation, and time to target temperature was 286 ± 196 minutes. Patients with favorable neurologic outcomes had lower Mg levels at presentation (2.1 mg/dL vs. 2.2 mg/dL, p = 0.010; OR [95% CI] = 0.531 [0.329-0.857]) and more frequently received Mg supplementation (39% vs. 25%, p = 0.009; OR [95% CI] = 1.936 [1.171-3.202]). Mg levels on presentation inversely correlated with favorable neurologic outcomes (r = -0.134, p = 0.036). Stratification of patients based on Mg levels demonstrated trends toward worse neurological outcomes at the extremes of the range, though sample sizes were small and the point estimate was not significant. ROC analysis showed no significant Mg level determining favorable outcomes. Mg levels at presentation inversely correlated with neurologic outcomes in cardiac arrest survivors undergoing TH. Intracellular shift and increased renal excretion of Mg may be responsible for the low Mg levels seen in some patients undergoing TH. Whether Mg supplementation could potentiate the beneficial effects of TH remains unclear and deserves further investigation.

Therapeutic hypothermia and targeted temperature management for traumatic brain injury: Experimental and clinical experience

Traumatic brain injury (TBI) is a worldwide medical problem, and currently, there are few therapeutic interventions that can protect the brain and improve functional outcomes in patients. Over the last several decades, experimental studies have investigated the pathophysiology of TBI and tested various pharmacological treatment interventions targeting specific mechanisms of secondary damage. Although many preclinical treatment studies have been encouraging, there remains a lack of successful translation to the clinic and no therapeutic treatments have shown benefit in phase 3 multicenter trials. Therapeutic hypothermia and targeted temperature management protocols over the last several decades have demonstrated successful reduction of secondary injury mechanisms and, in some selective cases, improved outcomes in specific TBI patient populations. However, the benefits of therapeutic hypothermia have not been demonstrated in multicenter randomized trials to significantly improve neurological outcomes. Although the exact reasons underlying the inability to translate therapeutic hypothermia into a larger clinical population are unknown, this failure may reflect the suboptimal use of this potentially powerful therapeutic in potentially treatable severe trauma patients. It is known that multiple factors including patient recruitment, clinical treatment variables, and cooling methodologies are all important in yielding beneficial effects. High-quality multicenter randomized controlled trials that incorporate these factors are required to maximize the benefits of this experimental therapy. This article therefore summarizes several factors that are important in enhancing the beneficial effects of therapeutic hypothermia in TBI. The current failures of hypothermic TBI clinical trials in terms of clinical protocol design, patient section, and other considerations are discussed and future directions are emphasized.

Therapeutic hypothermia in patients following traumatic brain injury: a systematic review.

The efficacy of therapeutic hypothermia in adult patients with traumatic brain injury is not fully understood. The historical use of therapeutic hypothermia at extreme temperatures was associated with severe complications and led to it being discredited. Positive results from animal studies using milder temperatures led to renewed interest. However, recent studies have not convincingly demonstrated the beneficial effects of therapeutic hypothermia in practice. This review aims to answer the question: in adults with a severe traumatic brain injury (TBI), does the use of therapeutic hypothermia compared with normothermia affect neurological outcome? Systematic review. Four major electronic databases were searched, and a hand search was undertaken using selected key search terms. Inclusion and exclusion criteria were applied. The studies were appraised using a systematic approach, and four themes addressing the research question were identified and critically evaluated. A total of eight peer-reviewed studies were found, and the results show there is some evidence that therapeutic hypothermia may be effective in improving neurological outcome in adult patients with traumatic brain injury. However, the majority of the trials report conflicting results. Therapeutic hypothermia is reported to be effective at lowering intracranial pressure; however, its efficacy in improving neurological outcome is not fully demonstrated. This review suggests that therapeutic hypothermia had increased benefits in patients with haematoma-type injuries as opposed to those with diffuse injury and contusions. It also suggests that cooling should recommence if rebound intracranial hypertension is observed. Although the data indicates a trend towards better neurological outcome and reduced mortality rates, higher quality multi-centred randomized controlled trials are required before therapeutic hypothermia is implemented as a standard adjuvant therapy for treating traumatic brain injury. Therapeutic hypothermia can have a positive impact on patient outcome, but more research is required.

Effects of therapeutic hypothermia and kinetics of serum protein S100B after cardiopulmonary resuscitation

Introduction. Post-resuscitation care is regulated by international guidelines. A milestone of these is the application of therapeutic hypothermia (TH). The aims of our study were: to determine the 30-day-mortality for our patients, to monitor the efficacy and effects of TH, and to investigate serum protein S100B – as an early prognostic marker.Materials and Methods. In our study, 57 patients, treated after cardiopulmonary resuscitation (CPR) on a multidisciplinary intensive care unit, were included. Patients were divided into groups who received and who didn’t receive TH. 30-day-mortality was determined as an end-point. Effects of TH were monitored using statistical analysis according to clinical parameters and laboratory tests. Serum protein S100B levels were measured with ELISA technique on 20 randomised patients atadmission and the 1st, 3rd and 5th day after CPR. Results. Total 30-day-mortality was 74%. TH did not reduced the 30-day-mortality (73% vs. 74%, p>0.05). We found a significant correlation between TH and serum lactate concentration after admission (0h,p=0.006) and at 12 (p=0.045) and 36 (p=0.049) hours after CPR. On the3rd (p=0.005) and 4th (p=0.043) day after CPR, as a result of TH, platelet count was significantly higher compared to normothermic samples. There was no significant difference in protein S100B levels between the normothermic and TH group and protein S100B levels did not correlate with 30-day-mortality.Conclusion. Despite recommendations of international guidelines, we cannot prove the beneficial effect of TH, or a correlation of protein S100B levels with a positive outcome.

Beneficial Effects of Nitric Oxide on Outcomes after Cardiac Arrest and Cardiopulmonary Resuscitation in Hypothermia-treated Mice

Therapeutic hypothermia (TH) improves neurological outcomes after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). Although nitric oxide prevents organ injury induced by ischemia and reperfusion, role of nitric oxide during TH after CPR remains unclear. In this article, the authors examined the impact of endogenous nitric oxide synthesis on the beneficial effects of hypothermia after CA/CPR. The authors also examined whether or not inhaled nitric oxide during hypothermia further improves outcomes after CA/CPR in mice treated with TH. Wild-type mice and mice deficient for nitric oxide synthase 3 (NOS3(−/−)) were subjected to CA at 37 °C and then resuscitated with chest compression. Body temperature was maintained at 37 °C (normothermia) or reduced to 33 °C (TH) for 24 h after resuscitation. Mice breathed air or air mixed with nitric oxide at 10, 20, 40, 60, or 80 ppm during hypothermia. To evaluate brain injury and cerebral blood flow, magnetic resonance imaging was performed in wild-type mice after CA/CPR. Hypothermia up-regulated the NOS3-dependent signaling in the brain (n = 6 to 7). Deficiency of NOS3 abolished the beneficial effects of hypothermia after CA/CPR (n = 5 to 6). Breathing nitric oxide at 40 ppm improved survival rate in hypothermia-treated NOS3(−/−) mice (n = 6) after CA/CPR compared with NOS3(−/−) mice that were treated with hypothermia alone (n = 6; P < 0.05). Breathing nitric oxide at 40 (n = 9) or 60 (n = 9) ppm markedly improved survival rates in TH-treated wild-type mice (n = 51) (both P < 0.05 vs. TH-treated wild-type mice). Inhaled nitric oxide during TH (n = 7) prevented brain injury compared with TH alone (n = 7) without affecting cerebral blood flow after CA/CPR (n = 6). NOS3 is required for the beneficial effects of TH. Inhaled nitric oxide during TH remains beneficial and further improves outcomes after CA/CPR. Nitric oxide breathing exerts protective effects after CA/CPR even when TH is ineffective due to impaired endogenous nitric oxide production.

The Effects of the Rate of Postresuscitation Rewarming Following Hypothermia on Outcomes of Cardiopulmonary Resuscitation in a Rat Model*

To investigate the optimal rewarming rate following therapeutic hypothermia in a rate model of cardiopulmonary resuscitation. Both clinical and laboratory studies have demonstrated that mild therapeutic hypothermia following cardiopulmonary resuscitation improves myocardial and neurologic outcomes of cardiac arrest. However, the optimal rewarming strategy following therapeutic hypothermia remains to be explored. Prospective randomized controlled experimental study. University-affiliated research institution. Twenty-three healthy male Sprague-Dawley rats. Four groups of Sprague-Dawley rats were randomized: 1) normothermia group (control), 2) rewarming rate at 2°C/hr, 3) rewarming rate at 1°C/hr, and 4) rewarming rate at 0.5°C/hr. Ventricular fibrillation was induced and untreated for 8 minutes, and defibrillation was attempted after 8 minutes of cardiopulmonary resuscitation. For the 2, 1, and 0.5°C/hr groups, rapid cooling was started at the beginning of cardiopulmonary resuscitation. On reaching the target cooling temperature of 33°C ± 0.2°C, the temperature was maintained with the aid of a cooling blanket until 4 hours after resuscitation. Rewarming was then initiated at the rate of 2.0, 1.0, or 0.5°C/hr, respectively, until the body temperature reached 37°C ±0.2°C. Blood samples were drawn at baseline and postresuscitation of 4, 6, 8, 10, and 12 hours for the measurements of blood gas and serum biomarkers. Blood temperature significantly decreased in the hypothermic groups from cardiopulmonary resuscitation to postresuscitation 4 hours. Significantly better cardiac output, ejection fraction, myocardial performance index, reduced neurologic deficit scores, and longer duration of survival were observed in the 1 and 0.5°C/hr groups. The increased serum concentration of troponin I, interleukin-6, and tumor necrosis factor-α was partly attenuated in the 1 and 0.5°C/hr groups when compared with the control and 2°C/hr groups. This study demonstrated that the severity of myocardial, cerebral injuries, and inflammatory reaction after cardiopulmonary resuscitation was reduced when mild therapeutic hypothermia was applied. A rewarming rate at 0.5-1°C/hr did not alter the beneficial effects of therapeutic hypothermia. However, a rapid rewarming rate at 2°C/hr abolished the beneficial effects of hypothermia.

Abstract 331: The Effects of the Rate of Post-resuscitation Rewarming following Hypothermia on Outcomes of CPR in a Rat Model

Background: Both clinical and laboratory studies have demonstrated that mild therapeutic hypothermia(TH) following CPR improves myocardial and neurologic outcomes of cardiac arrest. However, the optimal rewarming strategy following TH remains to be explored. The present study investigated the optimal rewarming rate following TH in a rat model of CPR. Methods and Results: Four groups of SD rats were randomized: 1) Control; 2) rewarming rate at 2°C/h; 3) rewarming rate at 1°C/h ; 4) rewarming rate at 0.5°C/h. VF was induced and untreated for 8 mins; defibrillation was attempted after 8 mins of CPR. The body temperature of the controls were maintained at 37±0.2°C throughout the experiment; For 2°C/h, 1°C/h and 0.5°C/h groups, rapid cooling was started with the aid of ice packs at the beginning of CPR. Upon reaching the target temperature of 33±0.2°C, the temperature was maintained with the aid of a cooling blanket until 4hrs after resuscitation. The rewarming was then initiated at the rate of 2.0°C, 1.0 °C or 0.5 °C per hour respectively until the body temperature reached 37±0.2 °C,which maintained at 37±0.2 °C for 6 hrs in 2 °C/h group, 4 hrs in 1 °C/h group, and 0 hours in 0.5 °C/h group. Blood samples were drawn at baseline, PR4, 6, 8, 10 and 12hrs for the measurements . Blood temperature was significantly decreased in the TH groups from CPR to PR 4hrs. Significantly better CO, EF, MPI and reduced neurological scores, longer duration of survival were observed in 1°C/hr and 0.5°C/hr groups. The increased serum levels of TnI, IL-6 and TNF-α was partly attenuated in 1°C/hr and 0.5°C/hr groups when compared with control and 2°C/hr groups. Conclusions: The present study demonstrated that the severity of myocardial, cerebral injuries and inflammatory reaction after CPR were reduced when mild TH was applied. A rewarming rate at 0.5-1°C/h did not alter the beneficial effects of TH. However, a rapid rewarming rate at 2°C/h abolished the beneficial effects of TH.

Abstract 217: Effect of Amiodarone with Therapeutic Hypothermia on Arrhythmia Substrates During Global Myocardial Ischemia

Background: The effect of therapeutic hypothermia (TH) after cardiac arrest on susceptibility to arrhythmias is not well understood. We have shown that TH has a beneficial effect on reentrant substrates for ischemia-induced arrhythmias by limiting decreases in conduction velocity (CV) and attenuating increases in transmural dispersion of repolarization (DOR). As amiodarone is utilized during TH, it is important to understand the effect of TH and amiodarone on arrhythmia substrates during ischemia. Our hypothesis is that amiodarone worsens the antiarrhythmic effect of TH during global ischemia. To test this hypothesis, a model of no flow global ischemia in the canine wedge preparation was used to study the effects of ischemia on all cell types spanning the transmural wall. Methods: Optical action potentials were recorded transmurally with high spatial (1 mm), temporal (.5 ms) and voltage (.5mv) resolution. Amiodarone (5microM) was used at both 36oC (control, CTAmio n=4) and 32oC (THAmio, n=4) during 15 min of no flow global ischemia and compared to controls (CT=7, TH=6). Action potential duration (APD), DOR, and CV were measured for all conditions. Programmed electrical stimulation (PES) was performed to assess for ischemia-induced arrhythmias and compared to prior controls (CT, n=5, TH, n=4). Results: At baseline, TH prolonged APD in both THAmio and TH, but there was no difference between DOR and CV. At 15 minutes of ischemia, DOR increased in the THAmio group compared to TH (34±3 ms to 79±9 ms vs. 25±3 to 37±7 ms, p=.04). There was a trend towards worsening ischemia-induced conduction slowing in the THAmio group vs TH, but not significant (39±4 to 24±3 cm/s vs 44±2 to 35±3 cm/s, p=.06). There was no difference under control temperature of CTAmio vs CT for CV, DOR, or APD. PES induced arrhythmias in 2/4 in the CTAmio group vs. 0/4 in THAmio group (compared to 3/5 in CT group, 1/4 in TH group). Conclusions: Amiodarone worsens the beneficial effect of TH on ischemia-induced DOR, but does not worsen susceptibility to arrhythmias. Further study in translatable models of ischemia-induced cardiac arrest is warranted to assess the effect of ACLS pharmacology on arrhythmias with the increased use of TH.

Abstract 338: Therapeutic Hypothermia for Patients With Post-Resuscitation Shock After Out-of-Hospital Cardiac Arrest

Background: Animal data have suggested a beneficial effect of therapeutic hypothermia following return of spontaneous circulation (ROSC) (post-ROSC cooling) in cardiogenic shock, but there are few human studies of patients with post-resuscitation shock who were treated with post-ROSC cooling. METHODS: From the J-PULSE HYPO registry, a multi-center registry in Japan, we selected the patients who met the following inclusion criteria: bystander-witnessed cardiac arrest due to ventricular fibrillation (VF), target core temperature of 32-34°C, and cooling duration of 12-72 hours. Study patients were divided into two groups based on hemodynamic status. The post-resuscitation shock group consisted of patients with systolic blood pressure &lt; 90 mmHg and/or mechanical circulation support. The remaining patients constituted the non-shock group. The primary endpoint was favorable neurological outcome at 30 days after cardiac arrest. Results: Of the 452 adult patients treated with post-ROSC cooling, 292 met the inclusion criteria; 149 (51%) were post-resuscitation shock and 143 (49%) were non-shock. No significant difference was observed between the two groups in the frequency of 30-day favorable neurological outcome (63% [94/149] post-resuscitation shock group vs. 68% [97/143] non-shock group; p=0.39). However, the median collapse-to-ROSC interval was significantly longer in the post-resuscitation shock group than in the non-shock group (27 minutes vs. 20 minutes, p&lt;0.001). In the quartiles of collapse-to-ROSC interval and 30-day favorable neurological outcome, both groups exhibited high frequencies of 30-day favorable neurological outcome in Quartile 1, in which the collapse to ROSC interval was 15 minutes or less (93% post-resuscitation shock group vs. 87% non-shock group, p=0.40), and a significant decrease in 30-day favorable neurological outcome was found in each group as the quartile value of collapse-to-ROSC interval increased (p&lt;0.001, respectively). The 30-day favorable neurological outcome in each Quartile 2, 3 and 4 did not differ between the two groups. Conclusion: Due to the effects of post-ROSC cooling, post-resuscitation shock patients were able to achieve the same level of neurological benefit as non-shock patients.