Therapeutic hypothermia after cardiac arrest

Endovascular Cooling Method for Hypothermia in Injured Swine

We evaluated an endovascular cooling method to modulate core temperature in trauma swine models with and without fluid support. Anesthetized swine (N = 80) were uninjured (SHAM) or injured through a bone fracture plus soft tissue injury or an uncontrolled hemorrhage and then subdivided to target body temperatures of 38°C (normothermia) or 33°C (hypothermia) by using a Thermogard endovascular cooling device (Zoll Medical). Temperature regulation began simultaneously at onset of injury (T0). Body temperatures were recorded from a rectal probe (Rec Temp) and from a central pulmonary artery catheter (PA Temp). At T15, swine received 500 mL IV Hextend over 30 minutes or no treatment (NONE) with continued monitoring until 3 hours from injury. Hypothermia was attained in 105 ± 39 minutes, at a cooling rate of -0.061°C ± 0.007°C/min for NONE injury groups. Postinjury Hextend administration resulted in faster cooling (-0.080°C ± 0.006°C/min); target temperature was reached in 83 ± 11 minutes (p < 0.05). During active cooling, body temperature measured by the PA Temp was significantly cooler than the Rec Temp due to the probe's closer proximity to the blood-cooling catheter balloons (p < 0.05). This difference was smaller in SHAM and fluid-supported injury groups (1.1°C ± 0.4°C) versus injured NONE groups (2.1°C ± 0.3°C). Target temperatures were correctly maintained thereafter in all groups. In normothermia groups, there was a small initial transient overshoot to maintain 38°C. Despite the noticeable difference between PA Temp and Rec Temp until target temperature was attained, this endovascular method can safely induce moderate hypothermia in anesthetized swine. However, likely due to their compromised hemodynamic state, cooling in hypovolemic and/or injured patients will be different from those without injury or those that also received fluids.

Evolution of insulin sensitivity and its variability in out-of-hospital cardiac arrest (OHCA) patients treated with hypothermia

INTRODUCTION

Therapeutic hypothermia (TH) is often used to treat out-of-hospital cardiac arrest (OHCA) patients who also often simultaneously receive insulin for stress-induced hyperglycaemia. However, the impact of TH on systemic metabolism and insulin resistance in critical illness is unknown. This study analyses the impact of TH on metabolism, including the evolution of insulin sensitivity (SI) and its variability, in patients with coma after OHCA.

METHODS

This study uses a clinically validated, model-based measure of SI. Insulin sensitivity was identified hourly using retrospective data from 200 post-cardiac arrest patients (8,522 hours) treated with TH, shortly after admission to the intensive care unit (ICU). Blood glucose and body temperature readings were taken every one to two hours. Data were divided into three periods: 1) cool (T <35°C); 2) an idle period of two hours as normothermia was re-established; and 3) warm (T >37°C). A maximum of 24 hours each for the cool and warm periods was considered. The impact of each condition on SI is analysed per cohort and per patient for both level and hour-to-hour variability, between periods and in six-hour blocks.

RESULTS

Cohort and per-patient median SI levels increase consistently by 35% to 70% and 26% to 59% (P <0.001) respectively from cool to warm. Conversely, cohort and per-patient SI variability decreased by 11.1% to 33.6% (P <0.001) for the first 12 hours of treatment. However, SI variability increases between the 18th and 30th hours over the cool to warm transition, before continuing to decrease afterward.

CONCLUSIONS

OCHA patients treated with TH have significantly lower and more variable SI during the cool period, compared to the later warm period. As treatment continues, SI level rises, and variability decreases consistently except for a large, significant increase during the cool to warm transition. These results demonstrate increased resistance to insulin during mild induced hypothermia. Our study might have important implications for glycaemic control during targeted temperature management.

Sublethal transient global ischemia stimulates migration of neuroblasts and neurogenesis in mice

Increasing evidence has shown the potential of neuronal plasticity in adult brain after injury. Neural proliferation can be triggered by a focal sublethal ischemic preconditioning event; whether mild global ischemia could cause neurogenesis has been not clear. The present study investigated stimulating effects of sublethal transient global ischemia (TGI) on endogenous neurogenesis and neuroblast migration in the subventricular zone (SVZ), dentate gyrus, and peri-infarct areas of the adult cortex. Adult mice of 129S2/Sv strain were subjected to 8-min bilateral common carotid artery ligation followed by 5-bromo-2'-deoxyuridine (BrdU; 50 mg/kg, intraperitoneal) administration every day until being sacrificed at 1-21 days after reperfusion. The mild TGI did not induce neuronal cell death for up to 7 days after TGI, as evidenced by negative terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining among NeuN-positive cells in the hippocampus and neocortex. In TGI animals, BrdU staining revealed enhanced proliferation of neuroblasts and their migration track from the SVZ into the striatum and neocortex. In the corpus callosum, there were more BrdU-positive cells in the TGI group in the first 2 days. Increasing numbers of BrdU-positive cells were seen 7-21 days later in the striatum and cortex of TGI mice. The cortex of TGI animals showed increased expression of erythropoietin, erythropoietin receptor, fibroblast growth factor 2, vascular endothelial growth factor, and phosphorylated Jun N-terminal kinase; the expression was peaked 2 to 3 days after reperfusion. BrdU and NeuN double staining in the dentate gyrus, striatum, and cortex implied increased neurogenesis induced by the TGI preconditioning. Doublecortin (DCX)-positive cells increased in the cortex of TGI mice, localized to cortical layers II, III, and V, and many stained positive for the mature neuronal markers NeuN, neurofilament, N-methyl-d-aspartic acid receptor subunit gene NR1, or the gamma-aminobutyric-acid-synthesizing enzyme glutamic acid decarboxylase (GAD67). The atypical localization of DCX-positive cells and the colabeling with mature neuronal markers suggested that, in addition to indentifying migrating neuroblasts, DCX might also be a stress marker in the cortex. It is suggested that the sublethal TGI-induced regenerative responses may contribute to the beneficial effects of ischemic preconditioning.

A novel mouse model of pediatric cardiac arrest and cardiopulmonary resuscitation reveals age-dependent neuronal sensitivities to ischemic injury

BACKGROUND

Pediatric sudden cardiac arrest (CA) is an unfortunate and devastating condition, often leading to poor neurologic outcomes. However, little experimental data on the pathophysiology of pediatric CA is currently available due to the scarcity of animal models.

NEW METHOD

We developed a novel experimental model of pediatric cardiac arrest and cardiopulmonary resuscitation (CA/CPR) using postnatal day 20-25 mice. Adult (8-12 weeks) and pediatric (P20-25) mice were subjected to 6min CA/CPR. Hippocampal CA1 and striatal neuronal injury were quantified 3 days after resuscitation by hematoxylin and eosin (H&E) and Fluoro-Jade B staining, respectively.

RESULTS

Pediatric mice exhibited less neuronal injury in both CA1 hippocampal and striatal neurons compared to adult mice. Increasing ischemia time to 8 min CA/CPR resulted in an increase in hippocampal injury in pediatric mice, resulting in similar damage in adult and pediatric brains. In contrast, striatal injury in the pediatric brain following 6 or 8 min CA/CPR remained extremely low. As observed in adult mice, cardiac arrest causes delayed neuronal death in pediatric mice, with hippocampal CA1 neuronal damage maturing at 72 h after insult. Finally, mild therapeutic hypothermia reduced hippocampal CA1 neuronal injury after pediatric CA/CPR.

COMPARISON WITH EXISTING METHOD

This is the first report of a cardiac arrest and CPR model of global cerebral ischemia in mice.

CONCLUSIONS

Therefore, the mouse pediatric CA/CPR model we developed is unique and will provide an important new tool to the research community for the study of pediatric brain injury.

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.

Hypothermic modulation of anoxic brain injury in adult survivors of cardiac arrest: a review of the literature and an algorithm for emergency physicians

Anoxic brain injury is a common outcome after cardiac arrest. Despite substantial research into the pathophysiology and management of this injury, a beneficial treatment modality has not been previously identified. Recent studies show that induced hypothermia reduces mortality and improves neurological outcomes in patients resuscitated from ventricular fibrillation. This article reviews the literature on induced hypothermia for anoxic brain injury and summarizes a treatment algorithm proposed by the Canadian Association of Emergency Physicians Critical Care Committee for hypothermia induction in cardiac arrest survivors.

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.

Hospital-based use of therapeutic hypothermia after cardiac arrest in adults

Improving survival and brain function after initial resuscitation from cardiac arrest remains a critical challenge with few therapeutic options. The publication of several randomized controlled trials supporting the use of therapeutic hypothermia in cardiac arrest survivors has provided a remarkable opportunity to reduce mortality and neurologic disability from this leading cause of death. On the strength of these trials, therapeutic hypothermia has now been incorporated in the American Heart Association guidelines for post-resuscitation care. This review will focus on the hospital-based application of therapeutic hypothermia in adult cardiac arrest survivors, with special attention to practical aspects of cooling, protocol development, and evaluation of recent data from "real world" experiences using hypothermia as a treatment option. Finally, remaining research questions and directions for future improvements in therapy will be discussed.

Therapeutic hypothermia for neuroprotection

This review briefly discusses induced therapeutic hypothermia (TH), which represents the intentional induction of a lowered core body temperature of 35 degrees C or less. The focus is on resuscitative or postarrest hypothermia, the data that support it, and the practical issues pertaining to TH implementation.

Predicting neurological outcome following cardiac arrest

Because a large number of patients will suffer cardiac arrest each year, physicians must place attention on improving care for patients in the post-resuscitative setting. Part of this effort requires setting realistic goals based on patients' potential for recovery. Recovery from cardiac arrest often depends on the extent of anoxic brain injury, and for this reason primary teams consult neurologists to offer insight into potential for awakening from post-arrest coma. In doing so, neurologists inform a decision with legal, social and ethical implications. Though inapplicable without preparation at the time of cardiac arrest, the four principles of medical ethics have a direct impact on decision making during the post-resuscitative period. A review of the literature reveals that physical examination, electrophysiology, radiology, and biochemical markers can prove useful in estimating a patient's chances for neurological recovery from cardiac arrest. These factors most reliably predict poor outcome, but do so with high specificity. However, the role of the neurology consultant must change to include guidance on strategies of neuroprotection. Aggressive efforts directed towards neuroprotection may change predictions for outcomes after cardiac arrest in the future.

Therapeutic hypothermia after cardiac arrest

Over recent years there has been growing evidence to support the use of hypothermia in post-cardiac arrest patients. Therapeutic hypothermia is now part of the UK Resuscitation Council guidelines in cardiac arrest, and has become part of many hospitals’ postcardiac arrest algorithm.

Neurocritical care: a distinct discipline?

PURPOSE OF REVIEW

We sought to review the evidence supporting neurocritical care as a distinct specialty of medicine.

RECENT FINDINGS

Over the past 20 years, neuro-intensive care units have evolved from neurosurgical units focused primarily on postoperative monitoring to units that provide comprehensive medical and specialized neurological support for patients with life-threatening neurological diseases. In addition to standard interventions, areas of expertise unique to neurocritical care include management of intracranial pressure, hemodynamic augmentation to improve cerebral blood flow, therapeutic hypothermia, and advanced neuromonitoring (i.e. continuous electroencephalography, brain-tissue oxygen, and microdialysis). Neurointensivists defragment care by focusing on the interplay between the brain and other systems, and by integrating all aspects of neurological and medical management into a single care plan. Outcomes research has established that victims of traumatic brain injury and hemorrhagic stroke experience reduced mortality, better functional outcomes, and reduced length of stay when cared for by neurointensivists in a dedicated neuro-intensive care unit. In the US a national system for accrediting training programs and certifying intensivists with special qualifications in neurocritical care is currently being established by the United Council of Neurologic Subspecialties.

SUMMARY

Neurocritical care is one of the newest subspecialties of medicine and is at the forefront of bringing effective new therapies to patients with life-threatening neurological diseases.

Resuscitative Value of B-Type Natriuretic Peptide in Comatose Survivors Treated With Hypothermia After Out-of-Hospital Cardiac Arrest due to Cardiac Causes

BACKGROUND

Two randomized studies have shown a neurological benefit of therapeutic hypothermia in comatose survivors after out-of-hospital cardiac arrest, but there are no studies of the cardiac neurohormone of B-type natriuretic peptide (BNP) in patients treated with hypothermia.

METHODS AND RESULTS

A prospective study was conducted of 109 comatose patients who were treated with mild hypothermia after out-of-hospital sudden cardiac arrest due to cardiac causes and whose BNP level was measured on arrival at the emergency room. The primary endpoint was a favorable neurological outcome at the time of hospital discharge. A total of 45 of the 109 patients had a favorable neurological outcome. The unadjusted rate of a favorable neurological outcome decreased in a stepwise fashion among patients in increasing quartiles of BNP level (p<0.001) and this association remained significant in subgroups of patients. The BNP cutoff value of 80 pg/ml for a favorable neurological outcome had an accuracy of 87.2%. In the multiple logistic-regression analysis, a BNP level of 80 pg/ml or less was an independent predictor of favorable neurological outcome.

CONCLUSIONS

The measurement of BNP was found to provide valuable information regarding the neurological outcome of comatose survivors treated with mild hypothermia after out-of-hospital cardiac arrest due to cardiac causes.

Cerebral resuscitation: state of the art, experimental approaches and clinical perspectives

Neuronal injury following global cerebral ischemia continues to bea central problem of patients in the postresuscitation phase following cardiocirculatory arrest. In addition to measures focusing on rapid restoration of spontaneous circulation, the most effective treatment after cardiac arrest, as shown by large randomized trials,is the use of therapeutic mild hypothermia. Current guidelines of the International Liaison Committee on Resuscitation (ILCOR)are recommending the use of therapeutic mild hypothermia for all unconscious patients after cardiac arrest. At present there is no specific neuroprotective treatment available. Promising animal experimental data concerning the use of thrombolytic agents during cardiopulmonary resuscitation have led to a large European multicenter trial (TROICA trial) that will provide its data in 2006.

Induction of mild hypothermia with infusion of cold (4°C) fluid during ongoing experimental CPR

INTRODUCTION

Therapeutic hypothermia after resuscitation has been shown to improve the outcome regarding neurological state and to reduce mortality. The earlier hypothermia therapy is induced probably the better. We studied the induction of hypothermia with a large volume of intravenous ice-cold fluid after cardiac arrest during ongoing cardiopulmonary resuscitation (CPR).

METHODS

Twenty anaesthetised piglets were subjected to 8 min of ventricular fibrillation, followed by CPR. They were randomized into two groups. The hypothermic group was given an infusion of 4 degrees C acetated Ringer's solution 30 ml/kg at an infusion rate of 1.33 ml/kg/min, starting after 1 min of CPR. The control group received the same infusion at room temperature. All pigs received a bolus dose of vasopressin after 3 min of CPR. After 9 min, defibrillatory shocks were applied to achieve restoration of spontaneous circulation (ROSC). Core temperature and haemodynamic variables were measured at baseline and repeatedly until 180 min after ROSC. Cortical cerebral blood flow was measured, using Laser-Doppler flowmetry.

RESULTS

All pigs had ROSC, except one animal in the hypothermic group. Only one animal in the hypothermic group died during the observation period. The calculated mean temperature reduction was 1.6+/-0.35 degrees C (S.D.) in the hypothermic group and 1.1+/-0.37 degrees C in the control group (p=0.009). There was no difference in cortical cerebral blood flow and haemodynamic variables.

CONCLUSION

Inducing hypothermia with a cold infusion seems to be an effective method that can be started even during ongoing CPR. This method might warrant consideration for induction of early therapeutic hypothermia in cardiac arrest victims.

Induced hypothermia is underused after resuscitation from cardiac arrest: a current practice survey

BACKGROUND

Important recent work has demonstrated that the use of induced hypothermia can improve survival and neurologic recovery after cardiac arrest. We wished to ascertain the extent to which physicians were using this treatment, and what opinions are held by clinicians regarding its use.

METHODS

An internet-based survey of physicians was conducted, with physicians chosen at random from published directories of the Society for Academic Emergency Medicine, the American Thoracic Society, and the American Heart Association. Physicians were questioned regarding use of therapeutic hypothermia, methods employed, and/or reasons why they had not incorporated hypothermia into their care of cardiac arrest patients.

RESULTS

Completed surveys were collected from 265 physicians, including those practicing emergency medicine (41%), critical care (13%), and cardiology (24%). Respondents were geographically well distributed and the majority (94%) were at post-training level. Most respondents (78%) practiced at either larger referral hospitals or academic medical centers. When asked if they had ever used hypothermia following cardiac arrest, 87% said they had not. Among reasons cited for non-use, 49% felt that there were not enough data, 32% mentioned lack of incorporation of hypothermia into advanced cardiovascular life support (ACLS) protocols, and 28% felt that cooling methods were technically too difficult or too slow.

CONCLUSION

Despite compelling data supporting its use, hypothermia has yet to be broadly incorporated into physician practice. This highlights the need for improved awareness and education regarding this treatment option, as well as the need to consider hypothermia protocols for inclusion in future iterations of ACLS.

Temperature effects on a whole metabolic reaction cannot be inferred from its components

Changes in temperature affect the kinetic energy of the constituents of a system at the molecular level and have pervasive effects on the physiology of the whole organism. A mechanistic link between these levels of organization has been assumed and made explicit through the use of values of organismal Q10 to infer control of metabolic rate. To be valid this postulate requires linearity and independence of the isolated reaction steps, assumptions not accepted by all. We address this controversy by applying dynamic systems theory and metabolic control analysis to a metabolic pathway model. It is shown that temperature effects on isolated steps cannot rigorously be extrapolated to higher levels of organization.

Intestinal ischemia reperfusion injury and multisystem organ failure

Intestinal ischemia-reperfusion is a common pathway for many diseases in infants, children, and adults, and this may lead to multiple organ dysfunction syndrome and death. While several studies have investigated reperfusion injury in cardiac, cerebral, and hepatic disease, limited work has been published on intestinal ischemia-reperfusion and its multiorgan effects. The authors have developed models of intestinal ischemia-reperfusion in rats and have demonstrated that intestinal reperfusion causes liver energy failure at normothermia. This is followed by 100% mortality within 4 hours of reperfusion. Moderate hypothermia (32 degrees C to 33 degrees C) induced throughout ischemia and reperfusion prevents liver energy failure, intestinal damage, and neutrophil infiltration in the lungs. Moderate hypothermia in this model of intestinal ischemia and reperfusion prevents mortality. Further studies are needed to establish whether therapeutic hypothermia is a useful intervention in the treatment of infants and children with intestinal injuries caused by ischemia and reperfusion.

Hypothermia after cardiac arrest: a treatment that works

PURPOSE OF REVIEW

Sudden death from cardiac arrest is a major health problem that still receives too little publicity. Current therapy after cardiac arrest concentrates on resuscitation efforts because, until now, no specific therapy for brain protection after restoration of spontaneous circulation was available. Therapeutic mild or moderate resuscitative hypothermia is a novel therapy with multifaceted chemical and physical effects by preventing or mitigating the derangements seen in the postresuscitation syndrome.

RECENT FINDINGS AND SUMMARY

In 2002, two prospective, randomized studies reported improved outcomes when deliberate hypothermia was induced in comatose survivors after resuscitation from cardiac arrest. However, several issues with regard to resuscitative cooling are still unanswered and should be studied further. These include the optimal timing to initiate cooling, the optimal cooling period, the optimal temperature level, and rewarming strategy. Even important questions, such as which cooling technique will be available in the near future that would combine ease of use with high efficacy, are not answered yet.

Cerebral ischemia and trauma-different etiologies yet similar mechanisms: neuroprotective opportunities

Cerebral ischemia leads to brain damage caused by pathogenetic mechanisms that are also activated by neurotrauma. These mechanisms include among others excitotoxicity, over production of free radicals, inflammation and apoptosis. Furthermore, cerebral ischemia and trauma both trigger similar auto-protective mechanisms including the production of heat shock proteins, anti-inflammatory cytokines and endogenous antioxidants. Neuroprotective therapy aims at minimizing the activation of toxic pathways and at enhancing the activity of endogenous neuroprotective mechanisms. The similarities in the damage-producing and endogenous auto-protective mechanisms may imply that neuroprotective compounds found to be active against one of these conditions may indeed be also protective in the other. This review summarizes the pathogenetic events of ischemic and traumatic brain injury and reviews the neuroprotective strategies employed thus far in each of these conditions with a special emphasize on their clinical relevance and on future directions in the field of neuronal protection.

Strain specific differences in a cardio-pulmonary resuscitation rat model

An asphyxial cardiac arrest rat model, originally developed for Sprague-Dawley rats, was transferred to a Wistar rat model. Several strain specific life support adjustments, i.e. ventilator settings, anaesthesia, and drug requirements, were necessary to stabilize the model for Wistar rats. Despite these arrangements numerous resuscitation related variables appeared different. Three groups were evaluated and compared: a temperature monitored Wistar group 1 (n=34), a temperature controlled Wistar group 2 (n=26) and a temperature controlled Sprague-Dawley group 3 (n=7). Overall, Wistar rats seem to have more sensitive cardio-circulatory system evidenced by a more rapid development of cardiac arrest (164 vs. 201 s), requiring higher adrenaline/epinephrine doses (10 vs. 5 microg/kg) and requiring more time for recovery after resuscitation (i.e. for return of blood pressure and blood gases). Without strict temperature control (as in groups 2+3 rats) group 1 rats went into spontaneous mild to moderate hypothermia during the first 24 h after restoration of spontaneous circulation (ROSC). Spontaneous hypothermia delayed the development of overall visible CA1 neuronal damage 24-48 h, but did not prevent it; therefore the model seemed to be suitable for future studies. Neuronal damages in the CA1 region in Wistar rats appeared to be more as shrunken cell bodies and pyknotic nuclei before resorption took place, whereas in Sprague-Dawley rats appeared in the same region.