How Chilling Helps Heal the Heart and Protect the Brain
When the call came to Piedmont Hospital in Atlanta, Ga., that 17-year-old Scott Dolezal had suffered a heart attack and had an abnormal heart rhythm (ventricular fibrillation), doctors in the emergency room were ready to start cooling his body as soon as he arrived. First they placed ice bags on his thighs and under his armpits, and then put gel pads on his thighs and chest that contained circulating cold water.
When the heart suddenly stops beating (called cardiac arrest), neurologic problems such as severe brain damage can develop because the brain stops getting enough oxygen. Clinical studies have shown that moderately cooling the body after a sudden cardiac arrest minimizes brain damage by protecting brain cells from injury and death.
After an out-of-hospital cardiac arrest that includes ventricular fibrillation, the American Heart Association recommends the patient be cooled to 32°C to 34°C (89.6°F to 93.2°F) for 12 to 24 hours. This technique, known as therapeutic hypothermia, also may be used if cardiac arrest is caused by pulseless electric activity (where the heart has a normal electrical rhythm but is not squeezing, usually due to a mechanical problem) or asystole (where there is no electrical activity in the heart), or if cardiac arrest happens in the hospital due to rhythm problems like an irregular or fast heartbeat.
The idea behind therapeutic hypothermia is to cool the brain in the hope of limiting the processes that lead to brain damage. “Cardiac arrest causes swelling in the brain triggered by inflammatory cells that, in turn, cause brain cells to die,” says Justin Lundbye, M.D., assistant professor of medicine at the University of Connecticut in Hartford.
Just as you put ice on an inflamed joint to help the swelling go down, cooling can act as an anti-inflammatory for the brain after cardiac arrest. Cooling lessens inflammation in brain tissue and slows down the body's metabolism, giving the brain and heart time to recover, says Lundbye.
As cooling takes place, body temperature and vital signs are monitored closely. In addition, the patient is given sedatives and muscle relaxants to prevent shivering, which can raise body temperature. After cooling is complete, a slow warming period of 12 hours or so is performed until body temperature returns to normal, and the patient is weaned off sedation.
Some people wake up as soon as the cooling stops, while others may take a week or more to recover fully. Scott woke up almost immediately with no signs of neurologic damage, says Anna Kalynych, M.D., interventional cardiologist at Piedmont Hospital. “By the time Scott went home, he was doing a Rubik's Cube in about 90 seconds,” she says.
THE RIGHT TEMP
Clinical studies show that more than half of cardiac arrest patients have a good neurologic outcome after therapeutic hypothermia. A mild drop in body temperature works well, but healthcare providers have learned from experience that too much of a drop can cause complications, such as bleeding (cooling decreases blood clotting) and heart arrhythmias. Getting the temperature just right is important. Side effects can happen, including infections and bleeding, but they are minor compared to the potential benefits. “We can give antibiotics and provide more blood to fix these side effects, but we can't treat permanent brain injury,” says Lundbye.
Over the past 10 years, most major medical centers in the United States have used therapeutic hypothermia to cool cardiac arrest patients as quickly as possible. At Hartford Hospital, emergency medical service (EMS) personnel infuse chilled saline into an arm vein of someone who has suffered a cardiac arrest on the way to the hospital. At the hospital emergency room, the chilled saline infusion continues and ice packs are applied to the groin and under the armpits while healthcare providers examine the patient. “Then our heart hypothermia team is activated, including doctors, nurses, and respiratory therapists, to assess the patient,” says Lundbye. If the patient needs faster cooling, the team inserts a catheter tipped with three balloons into a thigh vein, threads the catheter into the chest, and circulates cold water through the balloons to cool the body down in about one hour.
In New York City, more than 100 ambulances are equipped to start intravenous lines to infuse chilled saline as cardiac arrest patients are rushed to the hospital. Since New York instituted a therapeutic hypothermia program in January 2009, more than 2,600 cardiac arrest patients have been transported to dozens of hospitals citywide that provide the therapy, announced Mayor Michael Bloomberg one year ago.
PLAY IT COOL
“We are just at the beginning of a new era of therapeutic hypothermia,” says Lance Becker, M.D., professor of emergency medicine and director of the Center for Resuscitation Science at the University of Pennsylvania in Philadelphia, Pa. “Over the next 10 years, there will be many more devices developed that are easier to use, are more effective, and work faster. It's not important whether the therapeutic hypothermia team uses a fancy device or a bag of frozen French fries. They just have to achieve the goal of reducing body temperature.”
Luckily, everything came together for Scott, who could be the poster boy for successful therapeutic hypothermia. “Scott was young and otherwise healthy, but he had excellent CPR upfront, which helped his outcome,” says Kalynych. Early CPR, quick use of an automated external defibrillator to shock his heart, and fast response by the EMS to get him to the hospital gave Scott the opportunity to undergo the therapeutic hypothermia that helped save his life.
© 2011 American Heart Association, Inc.