Therapeutic Hypothermia
Chester J. Zelasko, Ph.D. | October 23, 2007

Medical progress sometimes moves forward by taking a step back. This Newsletter was prompted by two separate events. The first was an article in Newsweek about people who survived cardiac arrest (1). The second was a severe spinal-cord injury during a football game to Kevin Everett, a player for the Buffalo Bills.

In both cardiac arrest and severe spinal-cord injury, immediate cooling of the body seems to set the stage for improved outcomes. That translates to less brain damage to the cardiac-arrest patients and the ability to regain use of the limbs in severe spinal-cord injuries. In this Newsletter, I’m going to review the science behind therapeutic hypothermia after a cardiac arrest, stroke, pulmonary embolism, or damage to the spine. Then I’m going to give you some recommendations based on that science if you encounter someone having a heart attack.

The Premise
It’s very simple: when your heart stops or your spinal cord is crushed, the cells of the nervous system don’t die immediately. In the past, if someone’s brain had been without oxygen for longer than five minutes, the patient was thought to be beyond hope for recovery. But according to Dr. Lance Becker, Director of the University of Pennsylvania's Center for Resuscitation Science, the actual cell death may take hours or even days (1). For very complicated biochemical reasons, the typical solution--get the brain some oxygen as soon as possible--may actually contribute to cell death.

Cell death, more formally called apoptosis, was thought to be a given after oxygen deprivation--the process couldn't be stopped once it was underway because of a chain of events that includes inflammation, the production of free radicals, and the breakdown of cell components. That was thought to be the reason traditional therapy didn’t work.

Where did the idea come from that cooling the body may prevent cell death? While not certain, it seems that hypothermia victims were the likely source. You’ve probably heard stories about children trapped under the ice in cold water; there are many examples of children who have been resuscitated with no apparent neurological problems. The first documented case may have occurred over 170 years ago to a fisherman thrown overboard and rescued, but covered with ice and not breathing (2). He was gently re-warmed, and he recovered completely to resume his duties the next day. In all these cases, the heart stopped due to hypothermia but when restarted after the person was warmed, neurological recovery seemed complete.

The Science
Cooling the brain and heart has been used since the 1950s to slow tissue metabolism during surgery, but it wasn’t until the mid-1990s that the results of animal studies led to the first use of intentional cooling for cardiac-arrest patients (3). This has important implications, because most patients who suffer a cardiac arrest die after the event (4). In those who are successfully resuscitated, full neurological recovery occurs in only 6% to 23% of patients. If cooling the brain and nervous system creates a state of suspended animation, it might prevent the cause of cell death, which appears to be too much oxygen too soon after the heart is started.

Most studies to date have tried to establish the target temperature and the best way to lower the body temperature in clinical settings. While ice blankets and cold blankets work, infusion with saline solution cooled to 4 degrees C (39 F) can lower the body’s temperature to the desired temperature without causing complications (5). The key seems to be moderate cooling--that means cooling from the body’s typical temperature of 37 degrees C (98.6 F) to 32-34 degrees C (89.6-93.2 F). This led the Advanced Life Support (ALS) Task Force of the International Liaison Committee on Resuscitation (ILCOR) to recommend that people with cardiac arrest that occurs out of the hospital be cooled to 32-34 degrees C when the cause is fibrillation (6). They add that it may be appropriate for other neurological conditions as well. The patients are kept chilled for 24 to 72 hours, then their body temperature is slowly brought back to normal.

Knowing what to do is fine, but does it work? In the largest study to date, researchers compared the neurological recovery of a group of cardiac-arrest and shock patients with and without therapeutic hypothermia (7). Over half of the 43 patients who were cooled recovered neurological function compared to only 25% of the 43 in the non-cooled group. For those patients whose cardiac arrest was due to shock, one-third of those chilled recovered compared to none in the non-chilled group.

Clinical trials are currently underway to assess cooling for spinal-cord injuries. In the case of Kevin Everett, the team physician was familiar with current research on spinal-cord injuries, and the cooling process was begun on the way to the hospital. Despite the media attention cooling got during the Everett injury, therapeutic hypothermia hasn’t been approved as a therapy by any oversight group that deals with neurological injury. Still, due to the use of cooling in brain surgery and other neurological conditions, cooling to prevent nerve-cell death in such injuries may prove beneficial.

Bottom Line
Before the creators of urban legends start sending e-mails about packing heart-attack victims in ice, there are a couple of important things to know.

If you come across someone who has a heart attack and their heart is still beating, call the Emergency Medical Technicians (EMTs) immediately. At the risk of being obvious, no cardio-pulmonary resuscitation (CPR) is needed if the heart is beating.

If the heart is not beating, before you do anything else, call the EMTs. You have to get the professionals there as soon as possible--that’s always the most important thing to do. Then you should start CPR immediately and continue until the EMTs arrive. Remember, you do CPR only if you can’t get a pulse and the person is not breathing. If you don’t know CPR, take a class so you can be prepared. Once you start CPR, never stop until the EMTs take over. As long as circulation continues, there’s hope for recovery, even after an hour.

Resuscitation after therapeutic hypothermia works only with people who have a cardiac-arrest due to fibrillation; that means the electrical pathway in their heart has gone haywire and caused the heart to stop. If the heart stops for another reason--for example, parts of the heart have died--there’s little hope for resuscitation with therapeutic hypothermia or anything else; but since you won’t know what caused the heart to stop, your actions should be the same in any case where there’s no heartbeat.

The question is should you do anything to cool the person down? Right now, there are no recommendations either way, and you shouldn’t play doctor. But unless you’re in an area that’s extremely cold, don’t try to warm the person; if you’re in a warm area and there’s ice available, placing ice packs around the neck and the wrists (where the blood vessels are closest to the skin) while protecting the skin from frostbite may help begin the cooling process. The body needs to be cooled only a few degrees, so don’t overdo it. But let me repeat: keeping circulation moving is the most important action you can take, so don’t stop CPR until relieved by the EMTs.

In addition, you should know which hospitals in your area use therapeutic hypothermia as part of their treatment plan for cardiac arrest. As a runner, I’m going to add the name of the hospital I prefer to the information on the identification tag I wear when running. You might want to add that to the medical information you carry with you. (You do carry that in your wallet or purse, don’t you? A Newsletter for another time.)

As for Kevin, his prognosis has improved from quadriplegic to perhaps walking out of the hospital some day. Earlier this month, he was able to stand and walk with the assistance of a special harness. He continues to improve every day with the help of excellent surgeons who repaired the damage to his spinal cold, physical therapists who will help him learn to move again, and his family. Being chilled out never had a happier outcome.

References:
  1. Jerry Adler. Back from the Dead. NEWSWEEK. Jul 23, 2007.

  2. Bristow, G. et al. Resuscitation from cardiopulmonary arrest during accidental hypothermia due to exhaustion and exposure. Can Med Assoc Journal. 1977; 117:247-9.

  3. Sterz F, et al. Mild resuscitative hypothermia and outcome after cardiopulmonary resuscitation. J Neurosurg Anesthesiol. 1996; 8(1):88-96.

  4. Holzer M, Behringer W. Therapeutic hypothermia after cardiac arrest. Curr Opin Anaesthesiol. 2005 Apr;18(2):163-8.

  5. Polderman KH, et al. Induction of hypothermia in patients with various types of neurologic injury with use of large volumes of ice-cold intravenous fluid. Crit Care Med. 2005;33(12):2744-51.

  6. Therapeutic Hypothermia After Cardiac Arrest: An Advisory Statement by the Advanced Life Support Task Force of the International Liaison Committee on Resuscitation. Circulation 2003;108;118-121.

  7. Oddo M, et al. From evidence to clinical practice: effective implementation of therapeutic hypothermia to improve patient outcome after cardiac arrest. Crit Care Med. 2006;34(7):1865-73.
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