December 5, 2008

‘Cool’ protocol saves brain function after heart attack

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Former patient Gary Cook is able to enjoy quality time with his granddaughter, Addison Lynn Moreland.

‘Cool’ protocol saves brain function after heart attack

John McPherson, M.D.

John McPherson, M.D.

Gary Cook, 47, of Princeton, Ky., was preparing his coffee pot for the next morning's brew when his heart suddenly stopped beating and he collapsed to the kitchen floor.

His wife called 911 and ran next door to seek help from a new neighbor, who happened to be an emergency medical technician.

The EMT started CPR compressions but was not able to get a sustainable pulse or respiration. CPR kept Cook alive until he reached Caldwell Community Hospital, where emergency room physicians intubated him and restored his heartbeat.

Brain cells begin to die after approximately four minutes without oxygen, and Cook's brain had been deprived for 10 to 15 minutes. This condition is known as anoxic brain injury.

LifeFlight quickly transported Cook to Vanderbilt Heart & Vascular Institute, where physicians used a relatively new protocol to help limit the extent of brain damage caused by sudden cardiac arrest by lowering the patient's body temperature.

“His was a very high-risk situation. The risk of survival with meaningful neurologic outcome is statistically less than 10 percent in cases like this,” said John McPherson, M.D., medical director of the Cardiovascular Intensive Care Unit.

The therapeutic hypothermia protocol is the process of rapidly cooling the body temperature to 32 degrees Celsius (86 degrees Fahrenheit). It is implemented as soon as a patient arrives on the cardiovascular intensive care unit.

“It's a very complicated thing to do because it causes a lot of changes in the metabolic status of a patient,” McPherson said.

Once a good pulse is established in the patient, the cardiologist, in consult with the intensivist, begins the cooling process. They medically paralyze and completely sedate the patient. Paralysis prevents shivering, which is the body's way of raising its temperature.

Covers containing circulating cold water are placed over the patient's body and around the head. A machine slowly and carefully lowers the body temperature and maintains it for 24 hours from the onset of the initial injury.

“We think 32 degrees is low enough to attenuate any brain injury, but not too low to be excessively dangerous,” McPherson said.

Returning the patient to normal body temperature is also a very slow, controlled process that occurs at 1 degree Celsius every hour.

“This process is very intensive for nurses and physicians who must look for changes in blood pressure and metabolic status,” McPherson said.

How the cooling process actually limits brain damage is not fully understood. It appears to attenuate cell death and inflammation that occurs after anoxic brain injury, and prevents ongoing injury.

“What we're learning is that not all brain injury is irreversible, and a lot of permanent injury occurs in the first 24 hours, when cells at risk of dying may be prevented from dying if we can cool them down.”

Through rehabilitation Cook continues to regain his cognitive function.

“I used to be able to sit down and read an article or a technical manual and absorb it and know it. Now I have to reread several times to get it in my mind to remember it. I never used to make a list of things to do, phone calls to make, and now I have to list everything. It's a big change for me,” he said.

Cook recently sought out the physicians and nurses who took care of him to thank them for the care he received at Vanderbilt, realizing that without the therapeutic hypothermia protocol, he could have suffered permanent, extensive brain damage.

The protocol has been used in more than 25 patients so far, and plans include implementing it in the field where EMTs can begin the cooling process before the patient arrives at the hospital.