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:
- Jerry Adler. Back from the Dead. NEWSWEEK. Jul 23, 2007.
- Bristow, G. et al. Resuscitation from cardiopulmonary arrest during
accidental hypothermia due to exhaustion and exposure. Can Med Assoc
Journal. 1977; 117:247-9.
- Sterz F, et al. Mild resuscitative hypothermia and outcome after
cardiopulmonary resuscitation. J Neurosurg Anesthesiol. 1996;
8(1):88-96.
- Holzer M, Behringer W. Therapeutic hypothermia after cardiac arrest.
Curr Opin Anaesthesiol. 2005 Apr;18(2):163-8.
- 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.
- 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.
- 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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