Intra-arrest rapid head cooling improves postresuscitation myocardial function in comparison with delayed postresuscitation surface cooling

Conjunctival microcirculation is associated with cerebral cortex microcirculation in post-resuscitation mild hypothermia: A rat model

OBJECTIVE

This study aimed to compare the changes in sublingual and conjunctival microcirculation occurring with cerebral cortex microcirculation changes during mild hypothermia in a rat model of cardiac arrest.

METHODS

Twenty-four rats were randomized into mild hypothermia (M) or normothermia (C) groups. Ventricular fibrillation was electrically induced and left untreated for 8 minutes, followed by 8 minutes of cardiopulmonary resuscitation. The core temperature in group M reduced to 33 ± 0.5°C at 13 minutes after restoration of spontaneous circulation and was maintained for 8 hours. In group C, the core temperature was maintained at 37 ± 0.2°C. The hemodynamics and microcirculation in the sublingual region, bulbar conjunctiva, and cerebral cortex were measured at baseline and 1, 2, 3, 4, 6, and 8 hours after restoration of spontaneous circulation.

RESULTS

The M group showed significantly worse sublingual microcirculation at 6 hours post-resuscitation. However, microcirculation in the conjunctiva and cerebral cortex at 3 hours post-resuscitation were better in the M group. In the M group, microcirculation in the cerebral cortex was significantly correlated with that in the conjunctiva but not the sublingual microcirculation.

CONCLUSIONS

Changes in conjunctival microcirculation are closely related to cerebral cortex microcirculation during mild hypothermia, indicating that cerebral cortex microcirculation could be monitored by measuring conjunctival microcirculation.

Effect of mild hypothermia on cerebral microcirculation in a murine cardiopulmonary resuscitation model

BACKGROUND

We hypothesized that mild hypothermia may improve brain microcirculation by reducing cerebral microvascular endothelial cells apoptosis, and this effect may be maximized by moving up the initiation of mild hypothermia from after return of spontaneous circulation (ROSC) to the start of cardiopulmonary resuscitation (CPR).

METHODS

A total of 35 rats were randomized into the intra-arrest hypothermia group (IAH), post-resuscitation hypothermia group (PRH), normothermia group (NT), or the sham control group. A craniotomy exposed the parietal cortex for visualization of microcirculation. Ventricular fibrillation was electrically induced and untreated for 8 minutes, followed by 8 minutes of precordial compression and mechanical ventilation. Hypothermia (33 ± 0.5°C) in the IAH and PRH group was induced and maintained for 6 hours at the beginning of CPR or after ROSC, respectively. At baseline, 1, 3, and 6 hours, hemodynamic parameters were measured and the pial microcirculations were visualized with a sidestream dark field imaging video microscope. Microvascular flow index and perfused microvessel density (PMD) were calculated. Rats were euthanized, and brain tissues were removed at 3 and 6 hours separately. Expression of Bax, Bcl-2, and Caspase 3 in brain microvascular endothelial cells was examined by Western blot.

RESULTS

Microvascular flow index and PMD were significantly reduced after cardiac arrest and resuscitation (all P < 0.05), and the former was largely preserved by hypothermia regardless when the hypothermia treatment was induced (P < 0.05). Bax and Caspase 3 increased and Bcl-2 decreased significantly after resuscitation, and hypothermia treatment reversed the trend partly (all P < 0.05). A moderate correlation was observed between MFI and those proteins (Bcl-2/BAX: 3 hours: r = 0.730, P = 0.002; 6 hours: r = 0.743, P = 0.002).

CONCLUSION

Mild hypothermia improves cerebral microcirculatory blood supply, partly by inhibiting endothelial cell apoptosis. Mild hypothermia induced simultaneously with CPR has shown no additional benefit in microcirculation or endothelial cell apoptosis.

Effect of mild hypothermia on expression of inflammatory factors in surrounding tissue after minimally invasive hematoma evacuation in the treatment of hypertensive intracerebral hemorrhage

Mild hypothermia combined with minimally invasive hematoma evacuation was evaluated in the treatment of hypertensive intracerebral hemorrhage to reduce inflammatory response of brain tissue around hematoma and ameliorate brain function, and to investigate its safety, effectiveness and feasibility. A total of 206 patients with acute spontaneous hypertensive intracerebral hemorrhage were collected clinically and randomly divided into minimally invasive hematoma evacuation group (group A) and mild hypothermia combined with minimally invasive hematoma evacuation (group B). The National Institutes of Health Stroke Scale (NIHSS) score was used before and after treatment. Group A was treated with minimally invasive intracranial hematoma evacuation using intracranial hematoma grinding puncture needle while group B received whole body water circulation type cooling blanket plus local cerebral mild hypothermia therapy with ice cap on the basis of minimally invasive surgery. Patients brain tissue fragments around hematoma taken out with rinsing during operation and at postoperative 1, 3 and 7 days were investigated. The contents of tumor necrosis factor-α (TNF-α) in serum at postoperative 1, 3 and 7 days were evaluated by enzyme-linked immunosorbent assay (ELISA). For the degree of nerve function defect of patients in the two groups, NIHSS score was lower in group B than that in group A at days 3 and 7, and the differences were statistically significant (P<0.05). The serum TNF-α content and expression of nuclear factor-κB (NF-κB) in brain tissue around hematoma reached the peak on the 3rd day. The TNF-α content and NF-κB expression were lower in group B than those in group A at each time-point (P<0.05). Mild hypothermia combined with minimally invasive hematoma evacuation can reduce the damage of hematoma to the surrounding brain tissue, effectively alleviate inflammatory response and decrease brain tissue injury, thus ameliorating brain function.

Fast therapeutic hypothermia prevents post-cardiac arrest syndrome through cyclophilin D-mediated mitochondrial permeability transition inhibition

The opening of the mitochondrial permeability transition pore (PTP), which is regulated by the matrix protein cyclophilin D (CypD), plays a key role in the pathophysiology of post-cardiac arrest (CA) syndrome. We hypothesized that therapeutic hypothermia could prevent post-CA syndrome through a CypD-mediated PTP inhibition in both heart and brain. In addition, we investigated whether specific pharmacological PTP inhibition would confer additive protection to cooling. Adult male New Zealand White rabbits underwent 15 min of CA followed by 120 min of reperfusion. Five groups (n = 10-15/group) were studied: control group (CA only), hypothermia group (HT, hypothermia at 32-34 °C induced by external cooling at reperfusion), NIM group (injection at reperfusion of 2.5 mg/kg NIM811, a specific CypD inhibitor), HT + NIM, and sham group. The following measurements were taken: hemodynamics, echocardiography, and cellular damage markers (including S100β protein and troponin Ic). Oxidative phosphorylation and PTP opening were assessed on mitochondria isolated from both brain and heart. Acetylation of CypD was measured by immunoprecipitation in both the cerebral cortex and myocardium. Hypothermia and NIM811 significantly prevented cardiovascular dysfunction, pupillary areflexia, and early tissue damage. Hypothermia and NIM811 preserved oxidative phosphorylation, limited PTP opening in both brain and heart mitochondria and prevented increase in CypD acetylation in brain. There were no additive beneficial effects in the combination of NIM811 and therapeutic hypothermia. In conclusion, therapeutic hypothermia limited post-CA syndrome by preventing mitochondrial permeability transition mainly through a CypD-dependent mechanism.

Neurology of cardiopulmonary resuscitation

This chapter aims to provide an up-to-date review of the science and clinical practice pertaining to neurologic injury after successful cardiopulmonary resuscitation. The past two decades have seen a major shift in the science and practice of cardiopulmonary resuscitation, with a major emphasis on postresuscitation neurologic care. This chapter provides a nuanced and thoughtful historic and bench-to-bedside overview of the neurologic aspects of cardiopulmonary resuscitation. A particular emphasis is made on the anatomy and pathophysiology of hypoxic-ischemic encephalopathy, up-to-date management of survivors of cardiopulmonary resuscitation, and a careful discussion on neurologic outcome prediction. Guidance to practice evidence-based clinical care when able and thoughtful, pragmatic suggestions for care where evidence is lacking are also provided. This chapter serves as both a useful clinical guide and an updated, thorough, and state-of-the-art reference on the topic for advanced students and experienced practitioners in the field.

Remote Postconditioning Alone and Combined with Hypothermia Improved Postresuscitation Cardiac and Neurological Outcomes in Swine

Objective. Previously, we demonstrated that remote ischemic postconditioning (RIpostC) improved postresuscitation myocardial and cerebral functions in rat. Here, we investigated the effects of RIpostC alone and combined with therapeutic hypothermia (TH) on cardiac and neurological outcomes after CPR in swine. Methods. Twenty-one pigs were subjected to 10 mins of VF and then 5 mins of CPR. The animals were randomized to receive RIpostC alone, or its combination with TH, or sham control. RIpostC was induced by 4 cycles of limb ischemia followed by reperfusion. TH was implemented by surface cooling to reach a temperature of 32–34°C. Results. During 72 hrs after resuscitation, lower level of cardiac troponin I and greater stroke volume and global ejection fraction were observed in animals that received RIpostC when compared to the control. RIpostC also decreased serum levels of neuron-specific enolase and S100B and increased neurologic alertness score after resuscitation. The combination of RIpostC and TH resulted in greater improvement in cardiac and neurological outcomes than RIpostC alone. Conclusion. RIpostC was conducive to improving postresuscitation myocardial and cerebral functions and reducing their organ injuries. Its combination with TH further enhanced its protective effects.

Does therapeutic hypothermia during extracorporeal cardiopulmonary resuscitation preserve cardiac function?

Background

Extracorporeal cardiopulmonary resuscitation (E-CPR) is increasingly used as a rescue method in the management of cardiac arrest and provides the opportunity to rapidly induce therapeutic hypothermia. The survival after a cardiac arrest is related to post-arrest cardiac function, and the application of therapeutic hypothermia post-arrest is hypothesized to improve cardiac outcome. The present animal study compares normothermic and hypothermic E-CPR considering resuscitation success, post-arrest left ventricular function and magnitude of myocardial injury.

Methods

After a 15-min untreated ventricular fibrillation, the pigs (n = 20) were randomized to either normothermic (38 °C) or hypothermic (32–33 °C) E-CPR. Defibrillation terminated ventricular fibrillation after 5 min of E-CPR, and extracorporeal support continued for 2 h, followed by warming, weaning and a stabilization period. Magnetic resonance imaging and left ventricle pressure measurements were used to assess left ventricular function pre-arrest and 5 h post-arrest. Myocardial injury was estimated by serum concentrations of cardiac TroponinT and Aspartate transaminase (ASAT).

Results

E-CPR resuscitated all animals and the hypothermic strategy induced therapeutic hypothermia within minutes without impairment of the resuscitation success rate. All animals suffered a severe global systolic left ventricular dysfunction post-arrest with 50–70% reductions in stroke volume, ejection fraction, wall thickening, strain and mitral annular plane systolic excursion. Serum concentrations of cardiac TroponinT and ASAT increased considerably post-arrest. No significant differences were found between the two groups.

Conclusions

Two-hour therapeutic hypothermia during E-CPR offers an equal resuscitation success rate, but does not preserve the post-arrest cardiac function nor reduce the magnitude of myocardial injury, compared to normothermic E-CPR.

Trial registration FOTS 4611/13 registered 25 October 2012

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1099-y) contains supplementary material, which is available to authorized users.

Efficacy of Selective Brain Cooling Using a Nasopharyngeal Method in Piglets

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Controversies in the temperature management of critically ill patients

Although body temperature is a classic primary vital sign, its value has received little attention compared with the others (blood pressure, heart rate, and respiratory rate). This may result from the fact that unlike the other primary vital signs, aging and diseases rarely affect the thermoregulatory system. Despite this, when humans are exposed to various anesthetics and analgesics and acute etiologies of non-infectious and infectious diseases in perioperative and intensive care settings, abnormalities may occur that shift body temperature up and down. A recent upsurge in clinical evidence in the perioperative and critical care field resulted in many clinical trials in temperature management. The results of these clinical trials suggest that aggressive body temperature modifications in comatose survivors after resuscitation from shockable rhythm, and permissive fever in critically ill patients, are carried out in critical care settings to improve patient outcomes; however, its efficacy remains to be elucidated. A recent, large multicenter randomized controlled trial demonstrated contradictory results, which may disrupt the trends in clinical practice. Thus, updated information concerning thermoregulatory interventions is essential for anesthesiologists and intensivists. Here, recent controversies in therapeutic hypothermia and fever management are summarized, and their relevance to the physiology of human thermoregulation is discussed.

A review of compression, ventilation, defibrillation, drug treatment, and targeted temperature management in cardiopulmonary resuscitation

Objective:

Important studies of cardiopulmonary resuscitation (CPR) techniques influence the development of new guidelines. We systematically reviewed the efficacy of some important studies of CPR.

Data Sources:

The data analyzed in this review are mainly from articles included in PubMed and EMBASE, published from 1964 to 2014.

Study Selection:

Original articles and critical reviews about CPR techniques were selected for review.

Results:

The survival rate after out-of-hospital cardiac arrest (OHCA) is improving. This improvement is associated with the performance of uninterrupted chest compressions and simple airway management procedures during bystander CPR. Real-time feedback devices can be used to improve the quality of CPR. The recommended dose, timing, and indications for adrenaline (epinephrine) use may change. The appropriate target temperature for targeted temperature management is still unclear.

Conclusions:

New studies over the past 5 years have evaluated various aspects of CPR in OHCA. Some of these studies were high-quality randomized controlled trials, which may help to improve the scientific understanding of resuscitation techniques and result in changes to CPR guidelines.

Prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation model

BACKGROUND

Hypothermia when cardiopulmonary resuscitation begins may help achieve defibrillation and return of spontaneous circulation (ROSC), but few data are available.

OBJECTIVE

The objective of this study was to determine whether prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation (VF) model.

RESULTS

Thirty-six New Zealand rabbits were randomized equally to receive normothermia (Norm) (~39°C), post-ROSC hypothermia (~33°C), or prearrest hypothermia (~33°C). Ventricular fibrillation was induced by alternating current. After 4 minutes of VF, rabbits were defibrillated and given cardiopulmonary resuscitation until ROSC or no response (≥30 minutes). Hemodynamics and electrocardiogram were monitored; N-terminal pro-brain natriuretic peptideand troponin I were determined by enzyme-linked immunosorbent assay. Myocardial histology and echocardiographic data were evaluated. First-shock achievement of perfusion rhythm was more frequent in prearrest than normothermic animals (7/12 vs 1/12; P=.027). After ROSC, dp/dtmax was higher in prearrest than normothermic animals (P<.001). Left ventricular end-systolic pressure was higher in prearrest than normothermic animals (P=.001). At 240 minutes after ROSC, troponin I and N-terminal pro-brain natriuretic peptide were lower in prearrest than normothermic animals (15.74±2.26 vs 25.09±1.85 ng/mL and 426±23 vs 284±45 pg/mL, respectively), the left ventricular ejection fraction and cardiac output were lower in the Norm group than other 2 groups (P<.01). Myocardial histology was more disturbed in normothermic than post-ROSC and prearrest animals, but was not different in the latter 2 groups.

CONCLUSIONS

Induction of hypothermia before VF led to improved cardiac function in a rabbit VF model through improving achievement of perfusing rhythm by first-shock defibrillation and facilitating resuscitation.

Total liquid ventilation offers ultra-fast and whole-body cooling in large animals in physiological conditions and during cardiac arrest

INTRODUCTION

Total liquid ventilation (TLV) can cool down the entire body within 10-15 min in small animals. Our goal was to determine whether it could also induce ultra-fast and whole-body cooling in large animals using a specifically dedicated liquid ventilator. Cooling efficiency was evaluated under physiological conditions (beating-heart) and during cardiac arrest with automated chest compressions (CC, intra-arrest).

METHODS

In a first set of experiments, beating-heart pigs were randomly submitted to conventional mechanical ventilation or hypothermic TLV with perfluoro-N-octane (between 15 and 32 °C). In a second set of experiments, pigs were submitted to ventricular fibrillation and CC. One group underwent continuous CC with asynchronous conventional ventilation (Control group). The other group was switched to TLV while pursuing CC for the investigation of cooling capacities and potential effects on cardiac massage efficiency.

RESULTS

Under physiological conditions, TLV significantly decreased the entire body temperatures below 34 °C within only 10 min. As examples, cooling rates averaged 0.54 and 0.94 °C/min in rectum and esophageous, respectively. During cardiac arrest, TLV did not alter CC efficiency and cooled the entire body below 34 °C within 20 min, the low-flow period slowing cooling during CC.

CONCLUSION

Using a specifically designed liquid ventilator, TLV induced a very rapid cooling of the entire body in large animals. This was confirmed in both physiological conditions and during cardiac arrest with CC. TLV could be relevant for ultra-rapid cooling independently of body weight.

Mild hypothermia in combination with minimally invasive evacuation of hematoma reduces inflammatory damage in patients via the nuclear factor-κB pathway

The aim of this study was to investigate the effects of mild hypothermia and minimally invasive evacuation of hematoma on the brain function of patients with cerebral hemorrhage. Seventy-six patients with acute cerebral hemorrhage were divided into the minimally invasive evacuation of hematoma (MIHE) and mild hypothermia and minimally invasive evacuation of hematoma (MHMIHE) groups. National Institutes of Health Stroke Scale (NIHSS) scores on the day of admission of the patient and one, three and seven days after the procedure were recorded. Perihematoma brain tissue morphology was observed using hematoxylin and eosin staining. Nuclear factor-κB (NF-κB) expression was determined by immunohistochemistry. The tumor necrosis factor-α (TNF-α) level was detected by ELISA. NIHSS scores in the MHMIHE group were significantly lower than those in the MIHE group on days three and seven. TNF-α and NF-κB levels peaked on day three, and the MHMIHE group had significantly lower levels of TNF-α and NF-κB than the MIHE group. In conclusion, the present study demonstrated that mild hypothermia and minimally invasive evacuation of hematoma can effectively reduce inflammation and improve the brain function of patients.

Therapeutic hypothermia for neuroprotection: history, mechanisms, risks, and clinical applications

The earliest recorded application of therapeutic hypothermia in medicine spans about 5000 years; however, its use has become widespread since 2002, following the demonstration of both safety and efficacy of regimens requiring only a mild (32°C-35°C) degree of cooling after cardiac arrest. We review the mechanisms by which hypothermia confers neuroprotection as well as its physiological effects by body system and its associated risks. With regard to clinical applications, we present evidence on the role of hypothermia in traumatic brain injury, intracranial pressure elevation, stroke, subarachnoid hemorrhage, spinal cord injury, hepatic encephalopathy, and neonatal peripartum encephalopathy. Based on the current knowledge and areas undergoing or in need of further exploration, we feel that therapeutic hypothermia holds promise in the treatment of patients with various forms of neurologic injury; however, additional quality studies are needed before its true role is fully known.

The effects of the rate of postresuscitation rewarming following hypothermia on outcomes of cardiopulmonary resuscitation in a rat model

OBJECTIVE

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.

DESIGN

Prospective randomized controlled experimental study.

SETTING

University-affiliated research institution.

SUBJECTS

Twenty-three healthy male Sprague-Dawley rats.

INTERVENTIONS

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.

MEASUREMENTS AND MAIN RESULTS

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.

CONCLUSIONS

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.

Improved cardiac and neurologic outcomes with postresuscitation infusion of cannabinoid receptor agonist WIN55, 212-2 depend on hypothermia in a rat model of cardiac arrest

OBJECTIVES

To investigate the mechanisms of improved myocardial and neurological function and survival following i.v. administration of cannabinoid receptor agonist, WIN55, 212-2 in a rat model of cardiac arrest.

DESIGN

Prospective randomized controlled experimental study.

SETTING

University-affiliated research institute.

SUBJECTS

Thirty male Sprague-Dawley rats.

INTERVENTIONS

Ventricular fibrillation was electrically induced in 30 male Sprague-Dawley rats weighing between 450 and 550 g. Cardiopulmonary resuscitation was initiated after 6 minutes of untreated ventricular fibrillation. The precordial compression was performed with a pneumatically driven mechanical chest compressor. No pharmacological agent was used during cardiopulmonary resuscitation. After 8 minutes of cardiopulmonary resuscitation, up to three 2-J defibrillations were attempted. The animals were then randomized into three groups: 1) WIN55, 212-2 hypothermia, 2) WIN55, 212-2 with normal body temperature, and 3) placebo control. Either WIN55, 212-2 (1.0 mg/kg/hr) or saline placebo was continuously infused for 2 hours. Except for the WIN55, 212-2 hypothermia group, the body temperature in the other two groups was maintained at 37.0 ± 0.2°C using an external heating lamp. Postresuscitation myocardial function was measured by echocardiogram. Neurological deficit scores and survival time were observed for up to 72 hours.

MEASUREMENTS AND MAIN RESULTS

Blood temperatures decreased from 37°C to 33°C in 4 hours in animals in WIN55, 212-2 hypothermia group. Myocardial function, as measured by cardiac output, ejection fraction, and myocardial performance index, was significantly impaired in all animals after successful resuscitation when compared with the baseline values. There was a significant improvement in myocardial function in the animals treated with WIN55, 212-2 hypothermia beginning at 1 hour after start of infusion. However, no improvement was observed in the groups of WIN55, 212-2 with normal body temperature and placebo control. WIN55, 212-2 hypothermia group was associated with significantly improved neurologic deficit scores and survival time when compared with placebo control group and WIN55, 212-2 with normal body temperature group.

CONCLUSIONS

In a rat model of cardiac arrest, better postresuscitation myocardial function, neurological deficit scores, and longer duration of survival were observed by the pharmacologically induced hypothermia with WIN55, 212-2. The improved outcomes of cardiopulmonary resuscitation following administration of WIN55, 212-2 appeared to be the results from its temperature reduction effects.

Intra-arrest hypothermia during cardiac arrest: a systematic review

Introduction

Therapeutic hypothermia is largely used to protect the brain following return of spontaneous circulation (ROSC) after cardiac arrest (CA), but it is unclear whether we should start therapeutic hypothermia earlier, that is, before ROSC.

Methods

We performed a systematic search of PubMed, EMBASE, CINAHL, the Cochrane Library and Ovid/Medline databases using "arrest" OR "cardiac arrest" OR "heart arrest" AND "hypothermia" OR "therapeutic hypothermia" OR "cooling" as keywords. Only studies using intra-arrest therapeutic hypothermia (IATH) were selected for this review. Three authors independently assessed the validity of included studies and extracted data regarding characteristics of the studied cohort (animal or human) and the main outcomes related to the use of IATH: Mortality, neurological status and cardiac function (particularly, rate of ROSC).

Results

A total of 23 animal studies (level of evidence (LOE) 5) and five human studies, including one randomized controlled trial (LOE 1), one retrospective and one prospective controlled study (LOE 3), and two prospective studies without a control group (LOE 4), were identified. IATH improved survival and neurological outcomes when compared to normothermia and/or hypothermia after ROSC. IATH was also associated with improved ROSC rates and with improved cardiac function, including better left ventricular function, and reduced myocardial infarct size, when compared to normothermia.

Conclusions

IATH improves survival and neurological outcome when compared to normothermia and/or conventional hypothermia in experimental models of CA. Clinical data on the efficacy of IATH remain limited.

Ischemia hypothermia improved contractility under normothermia reperfusion in the model of cultured cardiomyocyte

Though mild hypothermia displays an optimistic alleviation of contractive failure in the ischemia/reperfusion myocardium, we still lacked answers to many questions about its potential mechanisms. Our hypothesis is that hypothermia (32°C) induced in ischemia can ease mitochondrial injury resulting in improvement of myocardial contractility even under the condition of a normothermic reperfusion. Fifty newly born 1-2 d Sprague-Dawley rats were executed and the primary cardiomyocytes were obtained and cultivated in vitro. Myocytes were randomized into three groups and then subjected to ischemia either at 32°C or 37°C, both prior to undergoing reperfusion at 37°C. Contractility was presented as frequency and velocity. Ultrastructural alterations of cardiomyocytes and mitochondrion underwent semi-quantitative analysis with transmission electron microscopy and respiratory function of mitochondria was further assessed simultaneously. During cooling ischemia and following reperfusion, cardiomyocytes acquired a more immediate restoration to baseline level and had a significant difference as compared with those in normothermia (P < 0.05). Furthermore, hypothermia preserved the ultrastructure of myocytes and mitochondrion after ischemia. However, measurement on Heart Injury Score and form factor revealed no differences after 2-h reperfusion either in hypothermia or normothermia. On the contrary, the surface area and respiratory function of mitochondrion in reperfusion differed significantly in both groups (P < 0.05) which had an accordance with the variation on contractile performance. Hypothermia only induced in ischemia can bring contractility benefit even under a normothermia reperfusion in cultured cardiomyocytes.

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.

Myocardial protection with mild hypothermia

Mild hypothermia, 32-35° C, is very potent at reducing myocardial infarct size in rabbits, dogs, sheep, pigs, and rats. The benefit is directly related to reduction in normothermic ischaemic time, supporting the relevance of early and rapid cooling. The cardioprotective effect of mild hypothermia is not limited to its recognized reduction of infarct size, but also results in conservation of post-ischaemic contractile function, prevention of no-reflow or microvascular obstruction, and ultimately attenuation of left ventricular remodelling. The mechanism of the anti-infarct effect does not appear to be related to diminished energy utilization and metabolic preservation, but rather to survival signalling that involves either the extracellular signal-regulated kinases and/or the Akt/phosphoinositide 3-kinase/mammalian target of rapamycin pathways. Initial clinical trials of hypothermia in patients with ST-segment elevation myocardial infarction were disappointing, probably because cooling was too slow to shorten normothermic ischaemic time appreciably. New approaches to more rapid cooling have recently been described and may soon be available for clinical use. Alternatively, it may be possible to pharmacologically mimic the protection provided by cooling soon after the onset of ischaemia with an activator of mild hypothermia signalling, e.g. extracellular signal-regulated kinase activator, that could be given by emergency medical personnel. Finally, the protection afforded by cooling can be added to that of pre- and post-conditioning because their mechanisms differ. Thus, myocardial salvage might be greatly increased by rapidly cooling patients as soon as possible and then giving a pharmacological post-conditioning agent immediately prior to reperfusion.

Ultrafast and whole-body cooling with total liquid ventilation induces favorable neurological and cardiac outcomes after cardiac arrest in rabbits

BACKGROUND

In animal models of cardiac arrest, the benefit afforded by hypothermia is closely linked to the rapidity of the decrease in body temperature after resuscitation. Because total liquid ventilation (TLV) with temperature-controlled perfluorocarbons induces a very rapid and generalized cooling, we aimed to determine whether this could limit the post-cardiac arrest syndrome in a rabbit model. We especially focused on neurological, cardiac, pulmonary, liver and kidney dysfunctions.

METHODS AND RESULTS

Anesthetized rabbits were submitted to either 5 or 10 minutes of untreated ventricular fibrillation. After cardiopulmonary resuscitation and resumption of a spontaneous circulation, the animals underwent either normothermic life support (control) or therapeutic hypothermia induced by TLV. The latter procedure decreased esophageal and tympanic temperatures to 32°C to 33°C within only 10 minutes. After rewarming, the animals submitted to TLV exhibited an attenuated neurological dysfunction and decreased mortality 7 days later compared with control. The neuroprotective effect of TLV was confirmed by a significant reduction in brain histological damages. We also observed limitation of myocardial necrosis, along with a decrease in troponin I release and a reduced myocardial caspase 3 activity, with TLV. The beneficial effects of TLV were directly related to the rapidity of hypothermia induction because neither conventional cooling (cold saline infusion plus external cooling) nor normothermic TLV elicited a similar protection.

CONCLUSIONS

Ultrafast cooling instituted by TLV exerts potent neurological and cardiac protection in an experimental model of cardiac arrest in rabbits. This could be a relevant approach to provide a global and protective hypothermia against the post-cardiac arrest syndrome.

Hypothermia improves ventricular myocyte contractility under conditions of normal perfusion and after an interval of ischemia

AIM

Recent investigations have reported improved myocardial function during hypothermia following resuscitation from cardiac arrest. The effects of hypothermia on myocyte contractility were investigated under conditions of normal perfusion and after a 10min interval of ischemia.

METHODS

Ventricular myocytes were obtained from 10 male Sprague-Dawley rats weighing 400+/-50g. The myocytes were randomized to be perfused at: 37 degrees C, 34 degrees C, 32 degrees C, or 30 degrees C. A subsequent set of myocytes was subjected to 10min of ischemia at 37 degrees C, prior to being randomized to reperfusion at: 37 degrees C, 34 degrees C, 32 degrees C or 30 degrees C. Myocyte contractility was expressed as length-shortening percentage. Intracellular Ca(2+) transients were assessed in a separate group of myocytes preloaded with Fura-2/AM. Sensitivity to Ca(2+) was tested by increasing perfusate Ca(2+) content, i.e. 0.5mM, 1mM and 2mM.

RESULTS

During normal perfusion and following reperfusion after 10min of ischemia, myocyte contractility increased at 34 degrees C compared to 37 degrees C (P<0.01). When the perfusion temperature was decreased to 32 degrees C and 30 degrees C, contractility further increased (P<0.001). Intracellular Ca(2+) transients were greater during perfusion at 34 degrees C compared to those at 37 degrees C (P<0.001) and further increased at 30 degrees C (P<0.001). Increases in extracellular Ca(2+) concentration from 0.5mM to 2mM resulted in greater myocyte contractility during perfusion at 30 degrees C compared to that observed at 37 degrees C (P<0.001). Effects of hypothermia on intracellular Ca(2+) transients and sensitivity to Ca(2+) persisted after ischemia.

CONCLUSIONS

Hypothermia improved myocyte contractility, intracellular Ca(2+) transients and sensitivity to Ca(2+) under conditions of normal perfusion and following reperfusion after 10min of ischemia.