Mild hypothermia during prolonged cardiopulmonary cerebral resuscitation increases conscious survival in dogs

Acute management of sudden cardiac death in adults based upon the new CPR guidelines

PURPOSE OF THE REVIEW

The aim of this article is to provide a comprehensive description of interventions that can improve outcomes in adults with sudden cardiac death. The new American Heart Association 2005 Guidelines introduced a number of changes for the initial management of cardiorespiratory arrest based on new data that accumulated over the last 5 years.

ACUTE MANAGEMENT OF SUDDEN CARDIAC DEATH

Appropriate interventions targeting the three phases of cardiopulmonary resuscitation (CPR) (electrical, circulatory, and metabolic) should be implemented. Early defibrillation in early witnessed arrest with one shock is very effective and can improve survival outcomes. When resuscitation efforts are delayed and CPR is performed by paramedics, 2 min of CPR before shock is recommended. Emphasis has been placed on fast and forceful continuous compressions with minimal interruptions, adequate decompression, and decrease in the rate of ventilations to 8-10/min for intubated patients with two rescuers and a universal increase in compression to ventilation ratio to 30:2 for lone rescuers. Mechanical adjuncts to improve circulation have been adapted in the recommendations. The inspiratory impedance threshold device that enhances negative intrathoracic pressure and improves venous preload has been recommended for application in intubated and bag-mask ventilated patients. Owing to the difficulty of endotracheal intubation, airway management devices (Combitube and Laryngeal Mask Airway) can be used as alternatives with minimal extra training.

CONCLUSION

The new guidelines for CPR have focused on early defibrillation, uninterrupted compressions, complete decompression, fewer ventilations, and simplification and uniformity of the process.

Hypothermia-induced cardioprotection using extended ischemia and early reperfusion cooling

Optimal timing of therapeutic hypothermia for cardiac ischemia is unknown. Our prior work suggests that ischemia with rapid reperfusion (I/R) in cardiomyocytes can be more damaging than prolonged ischemia alone. Also, these cardiomyocytes demonstrate protein kinase C (PKC) activation and nitric oxide (NO) signaling that confer protection against I/R injury. Thus we hypothesized that hypothermia will protect most using extended ischemia and early reperfusion cooling and is mediated via PKC and NO synthase (NOS). Chick cardiomyocytes were exposed to an established model of 1-h ischemia/3-h reperfusion, and the same field of initially contracting cells was monitored for viability and NO generation. Normothermic I/R resulted in 49.7 +/- 3.4% cell death. Hypothermia induction to 25 degrees C was most protective (14.3 +/- 0.6% death, P < 0.001 vs. I/R control) when instituted during extended ischemia and early reperfusion, compared with induction after reperfusion (22.4 +/- 2.9% death). Protection was completely lost if onset of cooling was delayed by 15 min of reperfusion (45.0 +/- 8.2% death). Extended ischemia/early reperfusion cooling was associated with increased and sustained NO generation at reperfusion and decreased caspase-3 activation. The NOS inhibitor N(omega)-nitro-L-arginine methyl ester (200 microM) reversed these changes and abrogated hypothermia protection. In addition, the PKCepsilon inhibitor myr-PKCepsilon v1-2 (5 microM) also reversed NO production and hypothermia protection. In conclusion, therapeutic hypothermia initiated during extended ischemia/early reperfusion optimally protects cardiomyocytes from I/R injury. Such protection appears to be mediated by increased NO generation via activation of protein kinase Cepsilon; nitric oxide synthase.

Hypothermia for cardiac arrest

Therapeutic hypothermia for cardiac arrest survivors has emerged as a highly effective means of improving neurologic outcome. There are a number of purported mechanisms by which it is felt to be effective, but the exact mechanism is unknown. This article reviews the biochemical mechanisms of injury occurring in cardiac arrest, as well as the avenues that hypothermia takes to combat this injury. It also reviews the animal model data in support of this, as well as the newer animal studies that may help to improve the field. Several human studies of hypothermia in cardiac arrest have been performed, and this article reviews these for their methods and shortcomings. Our currently recommended guidelines for performing therapeutic hypothermia are presented. With therapeutic hypothermia comes potential risks to the patient, primarily affecting cardiac, metabolic, and hematologic systems, and these risks and their management are discussed. Multiple methods of cooling exist, including selective cranial as well as systemic cooling by internal or external approaches. Finally, the article discusses the current research in the field of hypothermia for cardiac arrest and implications for future practice.

Brain tissue oxygen pressure and cerebral metabolism in an animal model of cardiac arrest and cardiopulmonary resuscitation

OBJECTIVE

Direct measurement of brain tissue oxygenation (PbtO2) is established during spontaneous circulation, but values of PbtO2 during and after cardiopulmonary resuscitation (CPR) are unknown. The purpose of this study was to investigate: (1) the time-course of PbtO2 in an established model of CPR, and (2) the changes of cerebral venous lactate and S-100B.

METHODS

In 12 pigs (12-16 weeks, 35-45 kg), ventricular fibrillation (VF) was induced electrically during general anaesthesia. After 4 min of untreated VF, all animals were subjected to CPR (chest compression rate 100/min, FiO2 1.0) with vasopressor therapy after 7, 12, and 17 min (vasopressin 0.4, 0.4, and 0.8 U/kg, respectively). Defibrillation was performed after 22 min of cardiac arrest. After return of spontaneous circulation (ROSC), the pigs were observed for 1h.

RESULTS

After initiation of VF, PbtO2 decreased compared to baseline (mean +/- SEM; 22 +/- 6 versus 2 +/- 1 mmHg after 4 min of VF; P < 0.05). During CPR, PbtO2 increased, and reached maximum values 8 min after start of CPR (25 +/- 7 mmHg; P < 0.05 versus no-flow). No further changes were seen until ROSC. Lactate, and S-100B increased during CPR compared to baseline (16 +/- 2 versus 85 +/- 8 mg/dl, and 0.46 +/- 0.05 versus 2.12 +/- 0.40 microg/l after 13 min of CPR, respectively; P < 0.001); lactate remained elevated, while S-100B returned to baseline after ROSC.

CONCLUSIONS

Though PbtO2 returned to pre-arrest values during CPR, PbtO2 and cerebral lactate were lower than during post-arrest reperfusion with 100% oxygen, which reflected the cerebral low-flow state during CPR. The transient increase of S-100B may indicate a disturbance of the blood-brain-barrier.

Critical time window for intra-arrest cooling with cold saline flush in a dog model of cardiopulmonary resuscitation

BACKGROUND

Mild hypothermia improves outcome when induced after cardiac arrest in humans. Recent studies in both dogs and mice suggest that induction of mild hypothermia during cardiopulmonary resuscitation (CPR) greatly enhances its efficacy. In this study, we evaluate the time window for the beneficial effect of intra-arrest cooling in the setting of prolonged CPR in a clinically relevant large-animal model.

METHODS AND RESULTS

Seventeen dogs had ventricular fibrillation cardiac arrest no flow of 3 minutes, followed by 7 minutes of CPR basic life support and 50 minutes of advanced life support. In the early hypothermia group (n=9), mild hypothermia (34 degrees C) was induced with an intravenous fluid bolus flush and venovenous blood shunt cooling after 10 minutes of ventricular fibrillation. In the delayed hypothermia group (n=8), hypothermia was induced at ventricular fibrillation 20 minutes. After 60 minutes of ventricular fibrillation, restoration of spontaneous circulation was achieved with cardiopulmonary bypass for 4 hours, and intensive care was given for 96 hours. In the early hypothermia group, 7 of 9 dogs survived to 96 hours, 5 with good neurological outcome. In contrast, 7 of 8 dogs in the delayed hypothermia group died within 37 hours with multiple organ failure (P=0.012).

CONCLUSIONS

Early application of mild hypothermia with cold saline during prolonged CPR enables intact survival. Delay in the induction of mild hypothermia in this setting markedly reduces its efficacy. Our data suggest that if mild hypothermia is used during CPR, it should be applied as early as possible.

Pediatric critical care community survey of knowledge and attitudes toward therapeutic hypothermia in comatose children after cardiac arrest

OBJECTIVE

Therapeutic hypothermia improves neurologic outcome and survival after adult out-of-hospital cardiac arrest. To help us design a prospective hypothermia trial in children, we developed a survey to assess current knowledge and attitude of pediatric critical care providers regarding therapeutic hypothermia and potential impediments to implementing a prospective study.

DESIGN

Anonymous survey.

SETTING

Internet-based survey of pediatric critical care community.

INTERVENTIONS

None.

RESULTS

A total of 159 responders completed the survey. Most respondents (92%) were fellowship-trained in pediatric critical care, with 9.9 +/- 6.5 yrs of experience. Many (85%) worked in the United States; 89% were in large tertiary care centers with residency or fellowship training programs. Most (65%) were aware of the adult randomized trials of therapeutic hypothermia, but only 9% (always) or 38% (sometimes) utilize this therapy. The most common reason to use hypothermia was likelihood of patient recovery, absence of life-limiting disease, and presence of coma for >/=1 hr after resuscitation. The majority of responders using therapeutic hypothermia cool their patients to 33-35 degrees C for a duration ranging from as short as 12 hrs to as long as 96 hrs; 91% do not actively rewarm the patient. A majority (81%) agree that a randomized, controlled trial of therapeutic hypothermia in children is ethical, and 95% would be willing to randomize their patients. Finally, 81% thought that therapeutic hypothermia should be studied in other ischemic insults and not just cardiac arrest.

CONCLUSIONS

Despite widespread awareness of therapeutic hypothermia's beneficial effects after arrest, it is not widely used by pediatric critical care clinicians sampled in our survey. Among those using hypothermia, there is wide variation in methodology and end points of therapy. This seems to result from a lack of evidence, difficulty with the technique, and unavailability of explicit protocols. Pediatric studies are needed to assess the safety, feasibility, and effectiveness of therapeutic hypothermia after cardiac arrest and other causes of brain injury.

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.

Therapeutic hypothermia after cardiac arrest

PURPOSE OF REVIEW

Most patients who suffer a cardiac arrest die after the event. Full neurological recovery occurs in only 6-23%. Until recently no specific post-arrest therapy was available to improve outcome. Application of therapeutic hypothermia (32-34 degrees C for 12-24 h) applied after cardiac arrest could help to improve this dreadful situation. This review covers the background of and recent clinical studies into hypothermia after cardiac arrest, and gives some insights into the future of resuscitation, namely suspended animation.

RECENT FINDINGS

Two randomized clinical trials of mild therapeutic hypothermia applied after successful resuscitation from cardiac arrest showed that hypothermia after cardiac arrest improves neurological outcome as well as overall mortality.

SUMMARY

The introduction of therapeutic hypothermia after cardiac arrest into routine intensive care practice could save thousands of lives worldwide, because only six patients must be treated to yield one additional patient with favourable neurological recovery. New developments in cooling techniques will make early induction of therapeutic hypothermia simple and convenient. The optimal duration and depth of hypothermia will be determined by future trials. Suspended animation is cooling during cardiac arrest to preserve the organism under conditions of prolonged controlled clinical death, followed by delayed resuscitation, resulting in survival without brain damage. This concept was initially introduced for trauma victims who rapidly bleed to death, and proved to be feasible in studies evaluating outcomes following exsanguination cardiac arrest in large animals. Whether the concept of suspended animation is applicable to normovolemic cardiac arrest is under investigation.