对心跳停止的急救低温治疗Therapeutic hypothermia for cardiac arrest

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Therapeutic hypothermia for cardiac arrest patients: Implementation and current recommendations.

In this special report we summarize recent reports that have reviewed the use of therapeutic hypothermia for reducing the risk for neurologic damage in resuscitated cardiac arrest patients, and outline possible barriers hindering its implementation.

Implementing therapeutic hypothermia after cardiac arrest

Sugerman N, Abella B. Hospital-based use of therapeutic hypothermia after cardiac arrest in adults. J Neurotrauma 2009;26:371–376. Kim F, Olsufka M, Nichol G, et al.

The use of pre-hospital mild hypothermia after resuscitation from out-of-hospital cardiac arrest. J Neurotrauma 2009;26:359–363.

The data for using therapeutic hypothermia to reduce mortality and neurologic disability in cardiac arrest patients is compelling and use of the technique in these patients has been endorsed by the International Liaison Committee on Resuscitation and the American Heart Association Emergency Cardiovascular Care Committee.

Yet recent surveys suggest that the technique has not been widely embraced by the medical community and uptake by hospitals has been slow.

Mr. Noah Sugerman and Dr. Benjamin Abella (University of Pennsylvania, Philadelphia, USA) note in their review that “real world” data on the implementation of therapeutic hypothermia in several individual institutions now exist and guidance on how to craft a protocol for implementing the technique has been issued by the Center for Resuscitation Science.

“After decades of research in the laboratory setting, the therapy has finally reached the bedside, and both protocols and cooling devices exist to help bring hospitals into the modern era of post-arrest care,” they say. There is also growing support for therapeutic hypothermia to be implemented in the field by the emergency medical services.

Most cardiac arrests occur outside of the hospital, note Dr. Francis Kim (University of Washington, Seattle, USA) and colleagues in a separate review. Also, animal studies suggest that “early cooling after return of spontaneous circulation, or even intra-arrest cooling, offers the best chance of neurologic recovery following sudden cardiac arrest.”

The need for portable refrigeration and easy administration pose challenges to the use of cooling in the field, but infusion of cold fluids has proved positive in pilot studies. Alternatives to intravenous cold fluids still being tested include cooling helmets, which have the added benefit of allowing local cooling to the brain reducing the possibility of systemic side effects, and cooling plates, which provide very rapid cooling. The use of pre-hospital cooling is still rare, note Kim et al. Problems that need addressing are short transport times, lack of refrigeration equipment, the receiving hospital’s failure to continue hypothermia, and a lack of clinical guidelines.

Clinical guidelines for hypothermia use in cardiac arrest patients

Castrén M, Silfvast T, Rubertsson S, et al. Scandinavian clinical practice guidelines for therapeutic hypothermia and post-resuscitation care after cardiac arrest. Acta Anaesthesiol Scand 2009;53:280–288.

The need for clinical guidelines has been recognized by the Clinical Practice Committee of the Scandinavian Society of Anaesthesiology and Intensive Care Medicine. They formed a task force to review the current literature on the use of therapeutic hypothermia after cardiac arrest to provide clinical practice recommendations.

The group recommends starting treatment as early as possible and maintaining it for 24 hours. Also, patients’ outcomes should not be decided until 72 hours after cardiac arrest to avoid early treatment withdrawal in patients who might still recover.

Despite therapeutic hypothermia use only being proven beneficial for cardiac arrest patients with initial ventricular fibrillation, the guidelines also recommend its use in patients with initial pulseless electrical activity and asystole – if active treatment is deemed necessary.

“Normal ethical considerations, premorbid status, total anoxia time, and general condition should decide whether active treatment is required or not,” say Prof. Maaret Castrén (Karolinska Institutet, Stockholm, Sweden) and colleagues.

Who stands to benefit from therapeutic hypothermia
Bernard S. Hypothermia after cardiac arrest: expanding the therapeutic scope. Crit Care Med 2009;37:S227–S233. Parham W, Edelstein K, Unger B, Mooney M.
Therapeutic hypothermia for acute myocardial infarction: past, present, and future. Crit Care Med 2009;37:S234–S237.

The idea that the therapeutic scope of hypothermia after cardiac arrest could be expanded to include patients who suffer non-ventricular fibrillation arrests and even those who suffer a cardiac arrest due to a non-cardiac cause is welcomed by Dr. Stephen Bernard (The Alfred Hospital, Melbourne, Victoria, Australia). He doubts that trials large enough to demonstrate a significant effect for therapeutic hypothermia in these patients will be undertaken because of the poor recovery rate among patients with initial asystole or pulseless electrical activity and the low incidence of arrest due to non-cardiac causes, such as drowning or accidental hanging. Nevertheless, he believes that, “given that therapeutic hypothermia has relatively few adverse effects and is now more easily implemented using currently available technology, it would appear reasonable for clinicians to cool most patients with suspected neurological injury following prolonged cardiac arrest, whatever the initial cardiac rhythm.”

The use of therapeutic hypothermia for protecting against neurologic damage in patients following acute myocardial infarction (MI) without cardiac arrest is not so readily recommended, however. In a separate review, Dr. William Parham and colleagues (Minneapolis Heart Institute and Abbott Northwestern Hospital, Minnesota, USA) observe that mild hypothermia can attenuate ischemia and reperfusion injury in cardiomyocytes. However, they found that, despite being cardioprotective in small-animal models of MI, these favorable effects of mild hypothermia have not been consistently demonstrated in larger animals.

Results from trials investigating the use of mild hypothermia for treating human ST-elevation myocardial infarction (STEMI) have also been mixed.

“Although mild hypothermia in STEMI patients appears feasible and safe, its routine efficacy for limiting infarct size or reducing the rates of major adverse cardiac events has yet to be demonstrated,” say Parham et al. “Therefore, its use in standard clinical practice cannot currently be recommended.”

Technique for inducing hypothermia

Jacobshagen C, Pax A, Unsöld BW, et al.
Effects of large volume, ice-cold intravenous fluid infusion on respiratory function in cardiac arrest survivors. Resuscitation 2009;Article in press.

Consensus on the best technique for inducing hypothermia is still lacking, but ice cold intravenous infusion appears to be a cheap and effective option.

Also recent study findings allay concerns that the technique might worsen respiratory function. Dr. Claudius Jacobshagen (Georg-August-University, Göttingen, Germany) and colleagues infused 52 patients resuscitated after cardiac arrest with a mean volume of 3427 mL of ice-cold fluid to reach a target temperature of 32–34 °C. This target was achieved after 4.1 hours. Left ventricular-function was significantly reduced, but the respiratory status of the patients did not deteriorate significantly. The ratio of mean partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FiO2) decreased slightly during infusion, but not significantly. The researchers also note that there was no significant correlation between the amount of infused fluid and the PaO2/ FiO2 ratio.
They recommend rapid infusion of high volumes of cold fluid to induce hypothermia in resuscitated cardiac arrest patients. But “it cannot be recommended to continue the rapid infusion of high volumes of cold fluid if the PaO2/ FiO2 ratio decreases seriously (oxygen saturation <94%),” the team says.

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