Therapeutic Hypothermia Improves Survival and Provides Cognitive Protection in Out Of Hospital Cardiac Arrest Patients

by Dr Sam Girgis on July 12, 2011

Cardiac arrest, or sudden cardiac death, results when the heart ceases to contract effectively enough to circulate the blood throughout the body.  Cardiac arrest can result from many different heart diseases including but not limited to heart attack, arrhythmia, or heart failure.  For decades, the treatment of cardiac arrest has been cardiopulmonary resuscitation (CPR) followed by early defibrillation if a shockable heart rhythm is the etiology.  Early defibrillation is a key to survival for some of these patients, and automated external defibrillators have been deployed in supermarkets, shopping mall, and airports to provide access to this life saving treatment.  Despite this, the survival of out of hospital cardiac arrest has been very poor with only 9-10% survival rates being observed.  On a yearly basis, an estimated 300,000 out of hospital cardiac arrests occur in the United States with the majority of these patients having bad outcomes that result in heart failure, neurological disability, and death.  The majority of cardiac arrest survivors do not return to their previous functional status due to the hypoxic encephalopathic injury that occurs.  There have been very few treatment interventions that have been able to change the prognosis for these patients.  Recently, therapeutic hypothermia has been shown to have a positive impact on survival as well as improve upon the post event neurological function of the surviving patients.  Physicians lead by Dr. Michael Mooney, from the Minneapolis Heart Institute, have provided additional evidence showing that therapeutic hypothermia improves survival of out of hospital cardiac arrest and ameliorates the associated neurological and cognitive impairment.  The results of their research were published online in the current issue of Circulation.  Between February of 2006 and August of 2009, the investigators evaluated 140 out of hospital cardiac arrest patients who remained unresponsive after being resuscitated.  These patients were treated with therapeutic hypothermia in an established regional network of hospitals that referred all eligible patients to a central therapeutic hypothermia treatment center.  The patients had cooling packs placed by responding emergency services personnel and continued the cooling process for the first 24 hours after cardiac arrest.  The core body temperature of the patients was lowered to 33 degrees Celsius, and neuromuscular blockade was used to prevent shivering.  After the 24 hour cooling period, core body temperature was raised by 0.5 degrees Celsius per hour until normal body temperature of 37 degrees Celsius was reached.  The investigators found that overall survival to hospital discharge was 56%, while 92% of those that survived to hospital discharge had a positive neurological outcome.  In addition, there was an observed 20% increased risk of death for every hour that therapeutic hypothermia was delayed.  The authors wrote, “We have demonstrated that simple cooling with ice bags initiated soon after arrest can be associated with incrementally improved outcomes, even if transfer to a specialized [therapeutic hypothermia] center is required, and that [therapeutic hypothermia] is an achievable standard of care that can be applied in urban and rural settings equally where regional systems of care have been developed”.  Therapeutic hypothermia is becoming increasingly recognized as an improvement to the current treatment protocols for out of hospital cardiac arrest.  To truly see the benefit of this treatment modality, it will have to be implemented across the already existent ST segment elevation myocardial infarction networks, and hopefully become more widely available throughout the United States and abroad.

Reference:

Michael R. Mooney et al. “Therapeutic Hypothermia After Out-Of-Hospital Cardiac Arrest:  Evaluation Of A Regional System to Increase Access To CoolingCirculation 2011; 124: 206-214.

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