Dallas, TX – Lowering the body temperature of a person who has been resuscitated after suffering cardiac arrest can help prevent brain damage, according to an international advisory statement published in Circulation: Journal of the American Heart Association.
The American Heart Association and resuscitation councils around the world helped craft the advisory from the Advanced Life Support Task Force of the International Liaison Committee on Resuscitation (ILCOR).
Cardiac arrest is the abrupt loss of heart function in a person who may or may not have diagnosed heart disease. No statistics are available for the exact number of sudden cardiac arrests that occur each year. But the American Heart Association estimates that about 250,000 people a year die of coronary heart disease without being hospitalized. That’s about half of all deaths from coronary heart disease – more than 680 Americans each day. Cardiac arrest results from the extremely rapid, chaotic quivering of the heart’s lower chambers, a disorder called ventricular fibrillation. It’s often reversible if treated within a few minutes with an electric shock to the heart from a defibrillator, a device that can allow a normal rhythm to resume.
Because the supply of oxygen-rich blood to the brain is cut off when the heart stops pumping, people who survive a cardiac arrest lasting more than a few minutes often suffer brain damage. Now, two major studies have shown that cooling the body temperature to below normal – mild therapeutic hypothermia – can help prevent that damage, says Jerry P. Nolan, M.D., lead author of the statement and co-chairman of the International Liaison Committee on Resuscitation’s Advanced Life Support Task Force.
The procedure, which aims to lower the body temperature to between 89.6 degrees F and 93.2 degrees F, should be started as soon as possible after successful resuscitation and continued for 12 to 24 hours, says Nolan, a consultant in anesthesia and critical care medicine at the Royal United Hospital in Bath, England.
Doctors have known for some time that reducing a person’s body temperature before the heart stops – such as when open-heart surgery is performed – can help prevent brain damage.
“What is so exciting about these new studies is that they showed that even if we cooled the brain after the oxygen supply had been cut off, people did better,” Nolan says.
In both studies, cardiac arrest survivors whose bodies were cooled were less likely to sustain neurological damage, compared with survivors who were not cooled.
A study in Europe used a special mattress with a cover that blew air over the body and used ice bags if necessary to cool the victims for 24 hours once they arrived at the critical care unit. In an Australian study, paramedics applied ice packs to patients’ heads and torsos, with ice applications continuing in the hospital for 12 more hours.
When a patient is successfully resuscitated and the supply of oxygen-rich blood to the brain is restored, it sets off a series of chemical reactions that can continue for up to 24 hours and can cause significant inflammation in the brain, Nolan says.
“Cooling slows down the chemical reactions, thereby lowering inflammation,” he says.
Many more questions remain to be answered – including how to best cool patients, how long they should be chilled, whether paramedics should be taught the procedure and when it’s too late to help. Cooling therapy carries a slightly increased risk of bleeding, infection and abnormal heart rhythms.
In addition, the cooling studies enrolled less than 10 percent of all cardiac arrest patients initially considered for treatment. Researchers studied only patients who met certain strict criteria – such as those with relatively known times of cardiac arrest, good blood pressure and evidence of coma after arrest. Further studies are needed to determine what other groups of cardiac arrest patients might benefit from cooling.
Nevertheless, the task force says the evidence that cooling prevents brain damage is compelling enough to recommend therapeutic hypothermia for some out-of-hospital cardiac arrest patients.
The American Heart Association urges people to call 9-1-1 and begin cardiopulmonary resuscitation (CPR) immediately if someone suffers cardiac arrest. If an automated external defibrillator (AED) is available and someone trained to use it is nearby, involve him or her.
However, grabbing a blanket and trying to warm up a cardiac arrest victim could do more harm than good, Nolan adds.
“The sooner the patient is successfully resuscitated and we can start cooling, the better,” he says.
Co-authors are Peter T. Morley; Terry L. Vanden Hoek, M.D.; and Robert W. Hickey, M.D.
The advisory is also supported by the European Resuscitation Council, Resuscitation Council of Southern Africa, Australia and New Zealand Council on Resuscitation, Japanese Resuscitation Council Latin American Resuscitation Council and the Heart and Stroke Foundation of Canada.