Mild resuscitative hypothermia to improve neurological outcome after cardiac arrest. A clinical feasibility trial. Hypothermia After Cardiac Arrest (HACA) Study Group

The injured nervous system: a Darwinian perspective

Much of the permanent damage that occurs in response to nervous system damage (trauma, infection, ischemia, etc.) is mediated by endogenous secondary processes that can contribute to cell death and tissue damage (excitotoxicity, oxidative damage and inflammation). For humans to evolve mechanisms to minimize secondary pathophysiological events following CNS injuries, selection must occur for individuals who survive such insults. Two major factors limit the selection for beneficial responses to CNS insults: for many CNS disease states the principal risk factor is advanced, post-reproductive age and virtually all severe CNS traumas are fatal in the absence of modern medical intervention. An alternative hypothesis for the persistence of apparently maladaptive responses to CNS damage is that the secondary exacerbation of damage is the result of unavoidable evolutionary constraints. That is, the nervous system could not function under normal conditions if the mechanisms that caused secondary damage (e.g., excitotoxicity) in response to injury were decreased or eliminated. However, some vertebrate species normally inhabit environments (e.g., hypoxia in underground burrows) that could potentially damage their nervous systems. Yet, neuroprotective mechanisms have evolved in these animals indicating that natural selection can occur for traits that protect animals from nervous system damage. Many of the secondary processes and regeneration-inhibitory factors that exacerbate injuries likely persist because they have been adaptive over evolutionary time in the healthy nervous system. Therefore, it remains important that researchers consider the role of the processes in the healthy or developing nervous system to understand how they become dysregulated following injury.

Induced hypothermia and fever control for prevention and treatment of neurological injuries

Increasing evidence suggests that induction of mild hypothermia (32-35 degrees C) in the first hours after an ischaemic event can prevent or mitigate permanent injuries. This effect has been shown most clearly for postanoxic brain injury, but could also apply to other organs such as the heart and kidneys. Hypothermia has also been used as a treatment for traumatic brain injury, stroke, hepatic encephalopathy, myocardial infarction, and other indications. Hypothermia is a highly promising treatment in neurocritical care; thus, physicians caring for patients with neurological injuries, both in and outside the intensive care unit, are likely to be confronted with questions about temperature management more frequently. This Review discusses the available evidence for use of controlled hypothermia, and also deals with fever control. Besides discussing the evidence, the aim is to provide information to help guide treatments more effectively with regard to timing, depth, duration, and effective management of side-effects. In particular, the rate of rewarming seems to be an important factor in establishing successful use of hypothermia in the treatment of neurological injuries.

Burning issues: early cooling of the brain after resuscitation using burn dressings. A proof of concept observation

AIM OF THE STUDY

Early cooling of resuscitated patients improves neurological outcome. Out-of hospital initiation of cooling is uncommon however for mainly practical reasons. Using burn dressings in the out-of-hospital care could initiate brain cooling in an early stage and therefore be of value; the method is easily adaptable by ambulance crews. The influence of burn dressings on brain temperature is however unknown. We determined tympanic temperature changes as proxy for brain temperature in healthy volunteers after the application of cooling dressings to face and neck as a proof of concept study.

METHOD

In 10 healthy human volunteers tympanic temperatures were measured in 30s intervals before, during and after the application of burn-dressings, special trauma burn-care dressings that are designed for the acute treatment of skin burns (Burnshield emergency burn care sterile trauma burn dressings, Burnshield Ltd., Wadefield, South Africa) for the duration of 20min for each episode.

RESULTS

In all study subjects the tympanic temperature was significantly lowered after 20min of the application of the burnshields. The mean difference between baseline and 2nd half of the exposure period was 0.43 degrees C (p<0.0001), ranging from 0.10 to 1.18 degrees C.

CONCLUSION

Burn dressings could be of value in the early initiation of brain cooling in resuscitated patients. This study warrants further research to the effect of burnshield dressings on neurological activity and the effect on outcome after resuscitation.

Use of induced hypothermia for neuroprotection: indications and application

Therapeutic temperature regulation has become an exciting field of interest. Mild-to-moderate hypothermia is a safe and feasible management strategy for neuroprotection and control of intracranial pressure in neurological catastrophies such as traumatic brain injury, subarachnoid and intracerebral hemorrhage, and large hemispheric stroke. Fever is associated with worse neurological outcome in patients with brain injury, normothermia may be of benefit in this patient population. The efficacy of mild-to-moderate hypothermia has been proven for neuroprotection after cardiac arrest with ventricular fibrillation as initial rhythm, and after neonatal asphyxia. Application of hypothermia and fever control in neurocritical care, available cooling technologies and systemic effects and complications of hypothermia will be discussed.

Efficacy of and tolerance to mild induced hypothermia after out-of-hospital cardiac arrest using an endovascular cooling system

Introduction

We evaluated the efficacy of and tolerance to mild therapeutic hypothermia achieved using an endovascular cooling system, and its ability to reach and maintain a target temperature of 33°C after cardiac arrest.

Methods

This study was conducted in the medical-surgical intensive care unit of an urban university hospital. Forty patients admitted to the intensive care unit following out-of-hospital cardiac arrest underwent mild induced hypothermia (MIH). Core temperature was monitored continuously for five days using a Foley catheter equipped with a temperature sensor. Any equipment malfunction was noted and all adverse events attributable to MIH were recorded. Neurological status was evaluated daily using the Pittsburgh Cerebral Performance Category (CPC). We also recorded the mechanism of cardiac arrest, the Simplified Acute Physiologic Score II on admission, standard biological variables, and the estimated time of anoxia. Nosocomial infections during and after MIH until day 28 were recorded.

Results

Six patients (15%) died during hypothermia. Among the 34 patients who completed the period of MIH, hypothermia was steadily maintained in 31 patients (91%). Post-rewarming 'rebound hyperthermia', defined as a temperature of 38.5°C or greater, was observed in 25 patients (74%) during the first 24 hours after cessation of MIH. Infectious complications were observed in 18 patients (45%), but no patient developed severe sepsis or septic shock. The biological changes that occurred during MIH manifested principally as hypokalaemia (< 3.5 mmol/l; in 75% of patients).

Conclusion

The intravascular cooling system is effective, safe and allows a target temperature to be reached fairly rapidly and steadily over a period of 36 hours.

Therapeutic hypothermia for global and focal ischemic brain injury--a cool way to improve neurologic outcomes

BACKGROUND

Therapeutic hypothermia (TH) has been employed as a neuroprotective strategy for a wide array of clinical problems since the late 1940s. Animal studies have determined that the neuroprotective effect of hypothermia is pleiotropic, impacting many steps in both the ischemic cascade and reperfusion injury. Interest in the neuroprotective effects of TH for ischemic brain injury has been resurgent, fueled by both recent positive and negative clinical trials. A review of preclinical and clinical reports on TH in adult patients is provided in this article.

REVIEW SUMMARY

Animal data and several large clinical studies of mild to moderate TH (32 degrees C-34 degrees C) for global cerebral ischemia describe favorable neurologic outcomes, with few adverse effects. However, clinical implementation for global ischemia remains poor. Some animal data support a role for TH in focal cerebral ischemia, if instituted soon after the onset of ischemia, and in the setting of reperfusion. Clinical studies of TH for focal cerebral ischemia have so far been equivocal. The available data suggest that, despite sharing some common components in the ischemic cascade, focal and global cerebral ischemia are pathophysiologically disparate, and may respond to different neuroprotective strategies.

CONCLUSION

TH is a safe, effective neuroprotective strategy for global cerebral ischemia. Because of the neuroprotective efficacy of TH in adult comatose survivors of cardiac arrest, neurologists should advocate the implementation of this strategy. TH for focal ischemia is a promising therapeutic option, but requires more basic and clinical investigation.

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

OBJECTIVES

Therapeutic hypothermia (TH) after cardiac arrest (CA) improves outcomes in a fraction of patients. To enhance the administration of TH, we studied brain electrophysiological monitoring in determining the benefit of early initiation of TH compared to conventional administration in a rat model.

METHODS

Using an asphyxial CA model, we compared the benefit of immediate hypothermia (IH, T=33 degrees C, immediately post-resuscitation, maintained 6h) to conventional hypothermia (CH, T=33 degrees C, starting 1h post-resuscitation, maintained 12h) via surface cooling. We tracked quantitative EEG using relative entropy (qEEG) with outcome verification by serial Neurological Deficit Score (NDS) and quantitative brain histopathological damage scoring (HDS). Thirty-two rats were divided into 4 groups based on CH/IH and 7/9-min duration of asphyxial CA. Four sham rats were included for evaluation of the effect of hypothermia on qEEG.

RESULTS

The 72-h NDS of the IH group was significantly better than the CH group for both 7-min (74/63; median, IH/CH, p<0.001) and 9-min (54/47, p=0.022) groups. qEEG showed greater recovery with IH (p<0.001) and significantly less neuronal cortical injury by HDS (IH: 18.9+/-2.5% versus CH: 33.2+/-4.4%, p=0.006). The 1-h post-resuscitation qEEG correlated well with 72-h NDS (p<0.05) and 72-h behavioral subgroup of NDS (p<0.01). No differences in qEEG were noted in the sham group.

CONCLUSIONS

Immediate but shorter hypothermia compared to CH leads to better functional outcome in rats after 7- and 9-min CA. The beneficial effect of IH was readily detected by neuro-electrophysiological monitoring and histological changes supported the value of this observation.

Therapeutic Hypothermia after Cardiac Arrest: Performance Characteristics and Safety of Surface Cooling with or without Endovascular Cooling

INTRODUCTION

Various methods are available to induce and maintain therapeutic hypothermia after cardiac arrest, but little data is available comparing device-mediated cooling to simple surface methods in this setting.

METHODS

To assess the performance characteristics of simple surface cooling with or without an endovascular cooling catheter system, we retrospectively reviewed all cases of hypothermia for comatose survivors of cardiac arrest treated at a single academically affiliated urban hospital. Forty two comatose survivors of cardiac arrest were treated over a 3.5-year period. Hypothermia was induced and maintained by simple surface methods (ice packs, cooling blankets) with or without placement of an endovascular cooling catheter system with automated temperature feedback regulation.

RESULTS

Overall, the rate of active cooling was not different between patients treated with endovascular catheter-assisted hypothermia and patients treated with surface cooling alone. However, use of a larger (14 F) catheter was associated with faster cooling rates. Maintenance of goal temperature (33 degrees C) was far better controlled with the use of a cooling catheter. Use of surface cooling alone was associated with significant temperature overshoot. Patients treated with surface cooling alone spent more time bradycardic.

CONCLUSION

Use of an endovascular cooling catheter as part of a treatment protocol for hypothermia after cardiac arrest provides better control during maintenance of hypothermia, preventing temperature overshoot. Active cooling rates may be enhanced by the use of a larger cooling catheter.

Mismatch recovery of regional cerebral blood flow and brain temperature during reperfusion after prolonged brain ischemia in gerbils

BACKGROUND

Recovery of cerebral reperfusion after stroke or cardiac arrest can take a long time. We aimed to identify differences in the postischemic recovery of physiologic parameters between short and prolonged brain ischemia.

METHODS

Eighteen Mongolian gerbils were assigned to one of three groups: 5-minute (G5), 15-minute (G15), or 30-minute (G30) ischemia. With the use of our original microspectroscopy system, global ischemic reperfusion was performed. We measured changes in regional cerebral blood flow (r-CBF), microvessel diameter, and brain temperature (BrT) simultaneously. We also monitored somatosensory evoked potentials (SEPs) to evaluate electrophysiologic response.

RESULTS

Both G5 and G15 showed concurrent recovery of r-CBF and BrT with hyperemia and hyperthermia, respectively, 10 to 15 minutes after reperfusion. The increase in BrT was <1 degree C and recovered to baseline within 60 minutes after reperfusion. In G30, recovery of r-CBF was significantly delayed relative to that of BrT. The increase in BrT was >2 degrees C, peaking approximately 15 minutes after reperfusion, and then maintained increases of >1 degree C for 120 minutes. SEPs in G5 and G15 showed concomitant recovery with that of r-CBF, whereas SEP recovery in G30 was delayed relative to that of r-CBF, eventually disappearing. All except one of the G30 gerbils died within 24 hours, but all in G5 and G15 survived.

CONCLUSIONS

These results suggest that mismatch recovery of r-CBF and BrT after prolonged ischemia initiates metabolic derangement in brain tissue, leading to the electrochemical dysfunction and mortality.

Environmental Cold-Induced Injury

More than 650 deaths from hypothermia occur each year in the United States. Even minor deviation from normal temperature leads to important symptoms and disability. The most significant risk factors are advanced age, mental impairment, substance abuse, and injury. This article examines the incidence of hypothermia, its detrimental effect on trauma patients, and methods of rewarming the hypothermic patient. It also looks at the controversial protective role hypothermia might play in shock, organ transplantation, cardiac arrest, and brain injury. Finally, it examines cold injuries, including frostbite, chilblain, and trench foot, and makes recommendations for their treatment.

Clinical review: beyond immediate survival from resuscitation-long-term outcome considerations after cardiac arrest

A substantial body of literature concerning resuscitation from cardiac arrest now exists. However, not surprisingly, the greater part concerns the cardiac arrest event itself and optimising survival and outcome at relatively proximal time points. The aim of this review is to present the evidence base for interventions and therapeutic strategies that might be offered to patients surviving the immediate aftermath of a cardiac arrest, excluding components of resuscitation itself that may lead to benefits in long-term survival. In addition, this paper reviews the data on long-term impact, physical and neuropsychological, on patients and their families, revealing a burden that is often underestimated and underappreciated. As greater numbers of patients survive cardiac arrest, outcome measures more sophisticated than simple survival are required.

Rapidly induced hypothermia with extracorporeal lung and heart assist (ECLHA) improves the neurological outcome after prolonged cardiac arrest in dogs

PURPOSE

We reported previously that therapeutic hypothermia with extracorporeal lung and heart assist (ECLHA) improved neurological outcome after 15 min cardiac arrest (CA) in dogs, although 45 min was needed to achieve hypothermia. We now investigate whether rapidly induced hypothermia with ECLHA (RHE) would result in a better outcome than slowly induced hypothermia with ECLHA (SHE) in dogs.

METHODS

Fifteen mongrel female dogs were divided into two groups: an RHE (n = 7) and an SHE (n = 8) group. Normothermic ventricular fibrillation was induced for 15 min and the animals were resuscitated by ECLHA. Rapid hypothermia was induced with a heat exchanger added to the ECLHA circuit in the RHE group, and by immersing the drainage tube of the ECLHA circuit in an ice water bath in the SHE group. Hypothermia (33 degrees C) was maintained for 20 h. The dogs were weaned from ECLHA at 24 h after resuscitation and treated for 96 h; neurological deficit scores (NDS) were measured throughout this period.

RESULTS

It took 1.6+/-0.8 min to reach 33 degrees C in the RHE group and 49.5+/-12.1 min to reach 33 degrees C in the SHE group. There was no difference in survival rate between the two groups. The NDS at 96 h in the RHE group was better than that in the SHE group (26% (range: 10-28%) versus 32% (26-37%); p < 0.05) although there was no significant difference in NDS between the two groups until 72 h.

CONCLUSION

Rapid hypothermic induction might be an important factor to improve neurological outcomes in prolonged CA models.

Therapeutic hypothermia

Therapeutic hypothermia has been used for millennia, but in recent years was not in much clinical use due to an apparent high risk of complications. More recently, the benefits of induced therapeutic hypothermia have been rediscovered, mainly with the improvement in neurological outcome in out-of-hospital cardiac arrest victims. In addition, therapeutic hypothermia has been suggested to improve outcome in other neurological conditions such as traumatic brain injury, neonatal asphyxia, cerebrovascular accidents and intracranial hypertension. This article reviews the history of the discovery of therapeutic hypothermia, as well as the current therapeutic applications and ways to deliver this treatment. Cooling techniques and recovery processes, as well as potential complications are also reviewed. Clinicians caring for a wide variety of critically ill patients should be familiar with the use of therapeutic hypothermia.

Quantitative EEG and neurological recovery with therapeutic hypothermia after asphyxial cardiac arrest in rats

We test the hypothesis that quantitative electroencephalogram (qEEG) can be used to objectively assess functional electrophysiological recovery of brain after hypothermia in an asphyxial cardiac arrest rodent model. Twenty-eight rats were randomly subjected to 7-min (n = 14) and 9-min (n = 14) asphyxia times. One half of each group (n = 7) was randomly subjected to hypothermia (T = 33 degrees C for 12 h) and the other half (n = 7) to normothermia (T = 37 degrees C). Continuous physiologic monitoring of blood pressure, EEG, and core body temperature monitoring and intermittent arterial blood gas (ABG) analysis was undertaken. Neurological recovery after resuscitation was monitored using serial Neurological Deficit Score (NDS) calculation and qEEG analysis. Information Quantity (IQ), a previously validated measure of relative EEG entropy, was employed to monitor electrical recovery. The experiment demonstrated greater recovery of IQ in rats treated with hypothermia compared to normothermic controls in both injury groups (P < 0.05). The 72-h NDS of the hypothermia group was also significantly improved compared to the normothermia group (P < 0.05). IQ values measured at 4 h had a strong correlation with the primary neurological outcome measure, 72-h NDS score (Pearson correlation 0.746, 2-tailed significance <0.001). IQ is sensitive to the acceleration of neurological recovery as measured NDS after asphyxial cardiac arrest known to occur with induced hypothermia. These results demonstrate the potential utility of qEEG-IQ to track the response to neuroprotective hypothermia during the early phase of recovery from cardiac arrest.

Therapeutic hypothermia after cardiac arrest

Recent evidence supports the use of therapeutic hypothermia after cardiac arrest. This article reviews recent published studies and describes the pathophysiology of hypothermia. Nurses need to understand the physiology of hypothermia to provide care for patients receiving therapeutic hypothermia. A suggested protocol is included to help manage the care of these patients.

Successful resuscitation from cardiac arrest associated with extradural lidocaine in a dog

BACKGROUND

Extradural lidocaine exerts several adverse effects which are seldom fatal. While cardiac arrest following extradural lidocaine injection has been reported in human beings, it has not hitherto been reported in dogs.

OBSERVATIONS

The emergency management of a dog with complete urethral obstruction is described. We intended to perform vaginoscopy and cystostomy under extradural lidocaine anaesthesia, but cardiac asystole occurred a few minutes after injection. Resuscitation was successful. About 20 minutes later cardiac arrest recurred, and was treated successfully. The dog remained hypothermic for approximately 7 hours. Complete recovery without neurological deficit occurred the next day and the dog remained normal for at least 3 months. The probable cause of the problem was cranial lidocaine dispersion causing a drop in cardiac preload and cardiac arrest. The successful neurological outcome was attributed to early diagnosis and effective treatment. Hypothermia may have conferred cerebral protection during ischemia.

CONCLUSIONS

Extradural local anaesthetic administration is not without risk and the technique should be tailored to individual animals. Constant monitoring is required to detect potentially fatal complications and increase the likelihood of successful outcome.

Inducing hypothermia to decrease neurological deficit: literature review

AIM

This paper reports a literature review to examine the effectiveness of inducing hypothermia to decrease neurological deficit after out-of-hospital cardiac arrest.

BACKGROUND

After cardiac arrest, severe neurological impairment is a major problem. Outcome after anoxic brain injury following cardiac arrest varies from normal function to brain death. However, a large proportion of these patients are left with severe disability and completely dependent on others for basic needs. Since the 1950s, several studies have shown how hypothermia can be neuroprotective. Recently, these studies have been taken to human trials in populations experiencing out-of-hospital cardiac arrest.

METHODS

A literature search was conducted using the Ovid and MDConsult databases for the years 1966-2004 and the keywords included hypothermia, therapeutic hypothermia, and cardiac arrest. Only English language papers were retrieved. Six human trials were found.

RESULTS

All six studies showed improved neurological outcomes and four of these showed a decrease in mortality. Minimal complications exist from inducing mild hypothermia after cardiac arrest, and include decreased heart rate, increased systemic vascular resistance, transient electrolyte abnormalities (increased serum potassium and glucose), possible increase in pneumonia or other infectious processes, possible rebound hyperthermia, possible hypotension, and possible arrhythmias.

CONCLUSIONS

Based on the review of these studies and the recommendations from the Advanced Life Support Task Force of the International Liaison Committee on Resuscitation, advanced practice nurses should promote this practice, but look for further research on specific treatment recommendations.

Therapeutic Hypothermia after Cardiac Arrest

The use of IH for 24 hours in patients who remain comatose following resuscitation from out-of-hospital cardiac arrest improves outcomes. How-ever, the induction of hypothermia has several physiologic effects that need to be considered. A protocol for the rapid induction of hypothermia is described. At present, the rapid infusion of a large volume (40 mL/kg) of ice-cold crystalloid (ie, lactated Ringer's solution) would appear to be an inexpensive, safe strategy for the induction of hypothermia after cardiac arrest. Hypothermia (33 degrees C) should be maintained for 24 hours, followed by rewarming over 12 hours. Particular attention must be paid to potassium and glucose levels during hypothermia.

Multimodal Strategies for Resuscitating Injured Cells

Our cells and tissues are challenged constantly by exposure to extreme conditions that cause acute and chronic stress. Wounding at the cellular level is a common event, and results from cell exposure to supra-physiologic forces, or is the consequence of action by reactive chemical agents. An individual cellular wound results from either the alteration of protein or DNA structure, or the disruption of molecular assemblies, the most important of which is the cell's membranes. Tissue healing at the macroscopic level is a complex and coordinated process involving many different cell types while, in contrast, the wounds of individual cells heal primarily via biomolecular interactions. Like tissue wound healing, cellular wound healing involves the upregulation or acceleration of processes that are constitutively expressed in routine physiologic repair of cellular structures In addition, recent advances have been made in the identification of pharmaceutical strategies to aid the cellular repair response. Many of these strategies offer promise for augmenting the already present cellular repair mechanisms.

Extracorporeal venovenous cooling for induction of mild hypothermia in human-sized swine*

OBJECTIVE

Several cooling methods have been investigated for inducing mild hypothermia (33-36 degrees C) after cardiac arrest, brain trauma, or stroke. To achieve its best effect, therapeutic hypothermia has to be applied very early after the ischemic insult; otherwise, the beneficial effect would be diminished or even abrogated. The aim of this study was to investigate the effectiveness and safety of extracorporeal venovenous cooling as compared with endovascular cooling.

DESIGN

Swine were cooled in a randomized crossover design from 38 degrees C to 33 degrees C brain temperature, either with extracorporeal venovenous cooling or with endovascular cooling.

SETTING

Laboratory investigation.

SUBJECTS

Six swine of human size (85 to 101 kg).

INTERVENTIONS

Swine were randomly cooled with the first device, and after achieving the target brain temperature, re-warmed via the same technique and with heating lamps to baseline temperature. Then the other catheter was inserted and cooling was performed with the second device.

MEASUREMENTS

Brain, pulmonary artery and tympanic temperature, blood pressure, and heart rate were recorded continuously. Laboratory samples, including free hemoglobin, were taken at predefined temperature points during cooling. Comparisons between and within (baseline vs. 33 degrees C) the treatment groups were performed with the paired Student's t-test.

MAIN RESULTS

The time needed to reduce brain temperature from 38.0 degrees C to 33.0 degrees C was 41 +/- 17 mins with venovenous cooling and 126 +/- 37 mins with endovascular cooling (p = .001). Heart rate and mean arterial pressure decreased moderately during cooling and were significantly lower at 33 degrees C than at baseline in both groups, without differences between groups. None of the swine developed significant hemolysis, arrhythmias, or bleeding.

CONCLUSIONS

Extracorporeal venovenous cooling was an effective and safe method to rapidly induce therapeutic mild hypothermia in human-sized swine. It seems to be promising for further application and investigation in patients.

[Controlled mild-to-moderate hypothermia in the intensive care unit]

Controlled hypothermia is used as a therapeutic intervention to provide neuroprotection and (more recently) cardioprotection. The growing insight into the underlying pathophysiology of apoptosis and destructive processes at the cellular level, and the mechanisms underlying the protective effects of hypothermia, have led to improved application and to a widening of the range of potential indications. In many centres hypothermia has now become part of the standard therapy for post-anoxic coma in certain patients, but for other indications its use still remains controversial. The negative findings of some studies may be partly explained by inadequate protocols for the application of hypothermia and insufficient attention to the prevention of potential side effects. This review deals with some of the concepts underlying hypothermia-associated neuroprotection and cardioprotection, and discusses some potential clinical indications as well as reasons why some clinical trials may have produced conflicting results. Practical aspects such as methods to induce hypothermia, as well as the side effects of cooling are also discussed.

[Therapeutic hypothermia after cardiac arrest]

The use of therapeutic hypothermia following different hypoxic-ischaemic insults has played an important role in various concepts of non-specific protection of cells for a long time. Although the use of deep therapeutic hypothermia after cardiac arrest in the last century did not lead to an improved outcome, recent data have demonstrated very positive effects of mild therapeutic hypothermia. The data from the European multicenter trial as well as those from Australia have clearly demonstrated a decrease in mortality and a better neurological outcome for patients being cooled to 32-34 degrees C for 12 or 24 h. In 2003, this led to the implementation of mild therapeutic hypothermia (32-34 degrees C) into the International Liaison Committee on Resuscitation (ILCOR) recommendations and guidelines for the treatment of unconscious patients after prehospital cardiac arrest. This article gives an overview on existing concepts and future perspectives of therapeutic mild hypothermia.

Cardiopulmonary bypass temperature and brain function

A debate has emerged in recently published studies about the optimum cardiopulmonary bypass temperature for good neurological outcome - warm vs. cold, i.e. normothermic vs. hypothermic. Although many comparative studies have been performed, the results of these studies are inconclusive and are difficult to interpret. Brain function has been studied in terms of neurological and neuropsychological outcome, protein S100beta levels as a marker of brain damage, and cerebral oxygenation using jugular bulb oximetry and near-infrared spectroscopy. The studies produce no conclusive proof of the superiority of warm or cold cardiopulmonary bypass. However, it appears that any degree of bypass hypothermia (< 35 degrees C) may protect the brain. On the other hand, even a slight increase in bypass temperature to > 37 degrees C may cause marked brain injury.

Hypothermia for neuroprotection after cardiac arrest: systematic review and individual patient data meta-analysis

OBJECTIVE

Only a few patients survive cardiac arrest with favorable neurologic recovery. Our objective was to assess whether induced hypothermia improves neurologic recovery in survivors of primary cardiac arrest.

DATA SOURCE

Studies were identified by a computerized search of MEDLINE, EMBASE, CINAHL, PASCAL, the Cochrane Controlled Trial Register, and BIOSIS.

STUDY SELECTION

We included randomized and quasi-randomized, controlled trials of adults who were successfully resuscitated, where therapeutic hypothermia was applied within 6 hrs after arrival at the emergency department and where the neurologic outcome was compared. We excluded studies without a control group and studies with historical controls.

DATA EXTRACTION

All authors of the identified trials supplied individual patient data with a predefined set of variables.

DATA SYNTHESIS

We identified three randomized trials. The analyses were conducted according to the intention-to-treat principle. Summary odds ratios were calculated using a random effects model and translated into risk ratios. More patients in the hypothermia group were discharged with favorable neurologic recovery (risk ratio, 1.68; 95% confidence interval, 1.29-2.07). The 95% confidence interval of the number-needed-to-treat to allow one additional patient to leave the hospital with favorable neurologic recovery was 4-13. One study followed patients to 6 months or death. Being alive at 6 months with favorable functional neurologic recovery was more likely in the hypothermia group (risk ratio, 1.44; 95% confidence interval, 1.11-1.76).

CONCLUSIONS

Mild therapeutic hypothermia improves short-term neurologic recovery and survival in patients resuscitated from cardiac arrest of presumed cardiac origin. Its long-term effectiveness and feasibility at an organizational level need further research.

A prospective, multicenter pilot study to evaluate the feasibility and safety of using the CoolGard System and Icy catheter following cardiac arrest

BACKGROUND

Cardiac arrest causes devastating neurological morbidity and mortality. Mild/moderate hypothermia is neuroprotective after global cerebral ischemia. More rapid controlled attainment of the target temperature may increase efficacy.

METHODS

We assessed the safety and feasibility of endovascular cooling in a single arm study of comatose patients who had been successfully resuscitated after cardiac arrest. Core temperature was reduced to a target of 33 degrees C for 24 h using a closed loop endovascular system placed in the inferior vena cava, followed by controlled rewarming. Primary outcomes were speed and accuracy of cooling, survival and GOS after 30 days.

RESULTS

Thirteen patients were enrolled, six male, age 60 +/- 19 years. Time from cardiac arrest to return of spontaneous circulation was 14.3 min (range 5-32.5). It took 3h and 39 min (median 210 min, IQ 80-315) to reach 33 degrees C; cooling averaged 0.8 +/- 0.3 degrees C/h (range 0.22-1.12 degrees C/h). Temperature was tightly maintained for all patients averaging 32.7 +/- 0.5 degrees C. Rewarming lasted 18.3 +/- 5.9 h. Five patients (38%) had 30-day Glasgow Outcome Scores of 1-2. Four patients died, none related to the hypothermia procedure. No unanticipated or procedure-related adverse events occurred.

CONCLUSION

In comatose survivors of cardiac arrest, hypothermia via endovascular methods is safe and feasible, and target temperatures can be achieved and controlled rapidly and precisely. More studies are needed to assess the efficacy of rapid endovascular hypothermia after cardiac arrest.

Moderate hypothermia for 359 operations to clip cerebral aneurysms

BACKGROUND

Experimental data have suggested that hypothermia (32-34 degrees C) may improve outcome after cerebral ischaemia, but its efficacy has not yet been established conclusively in humans. In this study we examined the feasibility and safety of deliberate moderate perioperative hypothermia during operations for subarachnoid aneurysms.

METHODS

A total of 359 operations for intracranial cerebral aneurysms were included in this prospective study. By using cold intravenous infusions (4 degrees C) and convective cooling our aim was to reduce the patient's core temperature to more than 34 degrees C within 1 h before operation. The protocol assessed postoperative complications such as infections, prolonged mechanical ventilation, pulmonary complications and coagulopathies.

RESULTS

During surgery, the body temperature was reduced to a mean of 32.5 (SD 0.4) degrees C. Cooling was accomplished at a rate of 4.0 (SD 0.4) degrees C h(-1). All patients were normothermic at 5 (sd 2) h postoperatively. Peri/postoperative complications included circulatory instability (n=36, 10%), arrhythmias (n=17, 5%) coagulation abnormalities and blood transfusion (n=169, 47%), infections (n=29, 8%) and pulmonary complications (infiltrate or oedema while on ventilatory support) (n=97, 27%). Eighteen patients died within 30 days (5%). There was no significant correlation between the extent of hypothermia and any of the complications. However, there was a strong correlation between the occurrence of complications and the severity of the underlying neurological disease as assessed by the Hunt and Hess score.

CONCLUSION

Moderate hypothermia accomplished within 1 h of induction of anaesthesia and maintained during surgery for subarachnoid aneurysms appears to be a safe method as far as the risks of peri/postoperative complications such as circulatory instability, coagulation abnormalities and infections are concerned.

The effect of mild therapeutic hypothermia on renal function after cardiopulmonary resuscitation in men

BACKGROUND

Mild therapeutic hypothermia (MTH) improves neurological outcome in patients after cardiac arrest. From animal and human studies it appears that hypothermia impairs renal function. The aim of this study was to examine the effects of MTH on renal function in humans.

METHODS

Patients were participants recruited in one of the centres of the hypothermia after cardiac arrest-multicenter trial. We measured serum creatinine and creatinine clearance (C(Cr)) within 24 h of MTH, at 4 hourly intervals. Patients were followed for acute renal failure and need for renal supportive therapy for 28 days.

RESULTS

We included 60 patients (32 hypothermic, 28 normothermic). Median serum creatinine on admission was [[119 micromol/l (IQR 108-133)] [1.35 mg/dl (IQR 1.22-1.50)]] in hypothermic and [[114 micromol/l (IQR 99-131)] [1.29 mg/dl (IQR 1.12-1.48)]] in normothermic patients, and decreased to [[69 micromol/l (IQR 62-84)] [0.78 mg/dl (IQR 0.70-0.95)]] in the hypothermic group and to [[88 micromol/l (IQR 71-123)] [1.00 mg/dl (IQR 0.80-1.39)]] in the normothermic group within 24h. C(Cr) was decreased on admission. Within 24 h C(Cr) improved to normal values in normothermic patients [1.53 ml/s (IQR 1.15-2.35) [92 ml/min (IQR 69-141)]] and remained low in hypothermic patients [0.88 ml/s (IQR 0.63-1.38) [53 ml/min (IQR 38-83)]] (P = 0.0006). No difference was found between the groups in the development of acute renal failure or the need for renal supportive therapy.

CONCLUSION

Twenty four hours of MTH was associated with a delayed improvement in renal function. This was not reflected in the serum creatinine values, which were low in the hypothermic group. This transient impaired renal function appeared to be completely reversible within 4 weeks.

Application of therapeutic hypothermia in the ICU: opportunities and pitfalls of a promising treatment modality. Part 1: Indications and evidence

OBJECTIVE

Hypothermia has been used for medicinal purposes since ancient times. This paper reviews the current potential clinical applications for mild hypothermia (32-35 degrees C).

DESIGN AND SETTING

Induced hypothermia is used mostly to prevent or attenuate neurological injury, and has been used to provide neuroprotection in traumatic brain injury, cardiopulmonary resuscitation, stroke, and various other disorders. The evidence for each of these applications is discussed, and the mechanisms underlying potential neuroprotective effects are reviewed. Some of this evidence comes from animal models, and a brief overview of these models and their limitations is included in this review.

RESULTS

The duration of cooling and speed of re-warming appear to be key factors in determining whether hypothermia will be effective in preventing or mitigating neurological injury. Some other potential usages of hypothermia, such as its use in the peri-operative setting and its application to mitigate cardiac injury following ischemia and reperfusion, are also discussed.

CONCLUSIONS

Although induced hypothermia appears to be a highly promising treatment, it should be emphasized that it is associated with a number of potentially serious side effects, which may negate some or all of its potential benefits. Prevention and/or early treatment of these complications are the key to successful use of hypothermia in clinical practice. These side effects, as well as various physiological changes induced by cooling, are discussed in a separate review.

Clinical trials for cytoprotection in stroke

To date, many cytoprotective drugs have reached the stage of pivotal phase 3 efficacy trials in acute stroke patients. (Table 1) Unfortunately, throughout the neuroprotective literature, the phrase "failure to demonstrate efficacy" prevails as a common thread among the many neutral or negative trials, despite the largely encouraging results encountered in preclinical studies. The reasons for this discrepancy are multiple, and have been discussed by Dr. Zivin in his review. Many of the recent trials have addressed deficiencies of the previous ones with more rigorous trial design, including more specific patient selection criteria (ensure homogeneity of stroke location and severity), stratified randomization algorithms (time-to-treat), narrowed therapeutic time-window and pharmacokinetic monitoring. Current trials have also incorporated biologic surrogate markers of toxicity and outcome such as drug levels and neuroimaging. Lastly, multi-modal therapies and coupled cytoprotection/reperfusion strategies are being investigated to optimize tissue salvage. This review will focus on individual therapeutic strategies and we will emphasize what we have learned from these trials both in terms of trial design and the biologic effect (or lack thereof) of these agents.

Hypothermia for Acute Ischemic Stroke: Not Just Another Neuroprotectant

BACKGROUND

Based on empirical experience, hypothermia has long been known to be a potent putative neuroprotectant. Recent insights into the mechanisms of central ischemia and reperfusion suggest reasons why hypothermia may be an ideal modality for extending the time window for thrombolytic stroke therapy.

REVIEW SUMMARY

Hypothermia protects brain tissue from the effects of ischemia in multiple ways. It retards energy depletion, reduces intracellular acidosis, and lessens the ischemic overdose of excitatory neurotransmitters. This attenuates the influx of intracellular calcium, the herald of subsequent neuronal death. Additionally, hypothermia suppresses synthesis of oxygen free radicals involved in secondary damage associated with reperfusion. It also suppresses the mechanisms related to blood-brain barrier degeneration and post-ischemic remodeling. Animal and human data show that deep hypothermia is primarily protective and is used in several cardiothoracic and neurosurgical applications, and that mild hypothermia enhances recovery after focal and global ischemic brain injuries. Preliminary data on hypothermia in human stroke also show promising potential. Current methods of instituting hypothermia, including patient selection, temperature and timing, cooling methods, and complications are reviewed in detail.

CONCLUSIONS

Neuroprotection conferred by mild to moderate hypothermia is likely to undergo phase III clinical trials in various clinical settings. Novel technology promises a broad application even outside intensive care settings. Preliminary studies suggest that mild to moderate hypothermia is a useful adjunct to thrombolytic therapy for stroke. Timing, degree, and duration rules are being developed and methods of cooling further perfected to optimize the safety and efficacy of this promising approach.

Induced hypothermia in critical care medicine: a review

BACKGROUND

Clinical trials of induced hypothermia have suggested that this treatment may be beneficial in selected patients with neurologic injury.

OBJECTIVES

To review the topic of induced hypothermia as a treatment of patients with neurologic and other disorders.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

Improved outcome was demonstrated in two prospective, randomized, controlled trials in which induced hypothermia (33 degrees C for 12-24 hrs) was used in patients with anoxic brain injury following resuscitation from prehospital cardiac arrest. In addition, prospective, randomized, controlled trials have been conducted in patients with severe head injury, with variable results. There also have been preliminary clinical studies of induced hypothermia in patients with severe stroke, newborn hypoxic-ischemic encephalopathy, neurologic infection, and hepatic encephalopathy, with promising results. Finally, animal models have suggested that hypothermia that is induced rapidly following traumatic cardiac arrest provides significant neurologic protection and improved survival.

CONCLUSIONS

Induced hypothermia has a role in selected patients in the intensive care unit. Critical care physicians should be familiar with the physiologic effects, current indications, techniques, and complications of induced hyperthermia.

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.

Failure of delayed and prolonged hypothermia to favorably affect hemorrhagic stroke in rats

Prolonged hypothermia reduces global and focal cerebral ischemic injury in rodents even when delayed for hours. However, it is not known whether hypothermia can reduce injury following intracerebral hemorrhage (ICH). Accordingly, we studied striatal injury and concomitant motor deficits after 2 days of hypothermia, induced 1 h after creation of an ICH by infusion of bacterial collagenase. Rats were first trained to retrieve food pellets in the Montoya staircase task. They were then implanted with core temperature telemetry probes and later subjected to normothermic ICH or sham operation (vehicle injection). Half self-regulated temperature after surgery; others were cooled to 33 degrees C (24 h) and then 35 degrees C (24 h). Hypothermia did not affect behavioral scores of sham animals (89.8% of baseline in staircase test) or histology. Untreated (normothermic) ICH rats lost 23.1 mm(3) of tissue at a 1-month survival, which significantly impaired food pellet retrieval (66.0% retrieval) with the contralateral limb (tested on days 21-25). Contrary to our hypothesis, hypothermia failed to lessen either the reaching impairment (62.8%) or the lesion (22.2 mm(3)). While other hemorrhagic insults or complications may be improved with hypothermia, our data suggest that it will not salvage tissue that is quickly lost after ICH. We also assessed walking across a horizontal ladder and spontaneous paw usage in a cylinder test at 1-4 weeks after ICH, but neither test was sufficiently sensitive to this mild insult. This indicates that skilled reaching is more severely disrupted than spontaneous paw usage or walking after a striatal hemorrhage.