Sudden cardiac arrest is a major public health concern, with more than 400,000 deaths annually in the United States alone. A patient's chance of survival drops by 7–10%/min when CPR is delayed after cardiac arrest. Widespread adherence to the new Advanced Cardiac Life Support/Emergency Cardiac Care guidelines for CPR and the increased use of therapeutic hypothermia may improve both of these statistics.

During cardiac arrest, spontaneous circulation ceases and the vital organs are not adequately perfused. If the patient is successfully resuscitated, circulation resumes, and reperfusion to the vital organs occurs. Reperfusion has been associated with free radical production which can lead to mitochondrial damage and programmed cell death. Mild hypothermia may suppress many of the chemical reactions associated with reperfusion injury.

In two prospective randomized trials comparing mild hypothermia (32–34°C) with normothermia in comatose survivors of out-of-hospital cardiac arrest favorable neurologic outcomes were observed. One study was conducted in five European countries and the other took place in four hospitals in Melbourne, Australia. The European study showed that cooling to 32–34°C for 24 hours decreased the chance of death (risk ratio, 0.74; 95% CI, 0.58–0.95) and increased the probability of good neurological outcome (risk ratio, 1.40; 95% CI, 1.08–1.81) (NEJM 2002; 346(8):549–556). The Australian study showed that cooling patients to 32–34°C for 12 hours increased the chance of good neurological recovery (risk ration 2.65; 95% CI, 1.02–6.88; p=0.046) (Bernard SA, et al. NEJM 2002; 346(8):557–563). Unlike in the studies of traumatic brain injury, no adverse outcomes were observed in cooled patients.

“Therapeutic hypothermia is one of the most exciting new therapies for cardiac arrest patients in the last decade,” Raina M. Merchant, MD, from the University of Chicago, comments. “It has already begun to have a major impact on outcomes from cardiac arrest. It is only a matter of time before we see patients not only survive cardiac arrest, but survive it well.”

Dr. Merchant says that American physicians are beginning to move forward with using this new therapy, especially in emergency rooms and intensive care units. In the next few years she predicts acceptance will improve and therapeutic hypothermia will be used frequently.

For more information on the therapy being practiced at the University of Chicago, please visit http://hypothermia.uchicago.edu.