Cardiac Arrest's Heartwarming Hope: Hypothermia
Dramatically cooling patients after cardiac arrest improves survival, recovery.
The woman was sitting in a friend’s car laughing at a joke when suddenly she slumped over, unresponsive. The panicked driver had the presence of mind to speed 15 blocks to the nearest hospital, the University of Chicago Medical Center, where doctors determined she had suffered a potentially lethal cardiac arrhythmia and worked to get her heart beating normally.
Then they put her on ice. The sedated woman’s body temperature was rapidly lowered, putting her in a state of mild hypothermia, and kept there.
“She should not have done well,” said Dr. David Beiser, one of the emergency-room physicians who treated the woman, “but we cooled her, and six days later she woke up.” The woman has since returned to work.
Roughly 90 percent of the 300,000 people who suffer cardiac arrest in the U.S. each year die, but a growing body of research shows that cooling a patient’s body to around 32-34 degrees Celsius (89-93 degrees Fahrenheit) after restarting the heart significantly improves survival.
Doctors may use ice packs, cooling blankets, an intravenous drip of chilled saline solution or special catheters with refrigerated tips to lower the patient’s core temperature and keep it there for up to 24 hours.
“Hypothermia represents one of the most important advances in cardiac care since the development of defibrillators 50 years ago,” said Dr. Benjamin Abella, an assistant professor of emergency medicine at the University of Pennsylvania. “If it was being aggressively implemented in hospitals, we would probably have thousands more survivors of cardiac arrest every year.”
Although cardiac arrest is “one of the most lethal conditions in medicine,” Abella said most doctors still are not using it on a routine basis. He co-authored a 2005 study showing that many wrongly believed there was insufficient evidence to adopt the procedure.
Cardiac arrest is not the same thing as a heart attack. In a myocardial infarction, a blocked coronary artery may cause chest pain and shortness of breath, but the condition can often be treated with clot-dissolving drugs, angioplasty or stents.
Cardiac arrest, where the heart loses its rhythm or stops beating altogether, may follow a heart attack or strike without warning. A sudden loss of consciousness results as blood flow to the brain stops, and if the heart is not restarted quickly, death follows.
A 2003 report in the American Heart Association journal Circulation found that prospective randomized trials in Europe and Australia had shown inducing mild hypothermia in comatose survivors of out-of-hospital cardiac arrest led to higher survival rates and fewer neurological complications.
In the European study, patients were kept chilled for 24 hours before being allowed to rewarm naturally. The study of 273 patients found 55 percent of the hypothermia group patients were living independently six months later, compared with 39 percent in a control group of patients who did not receive hypothermia treatment. And at six months, only 41 percent of the hypothermia group had died, while 55 percent of the un-chilled group had.
Doctors in the Australian study, conducted at four hospitals in Melbourne, used cold packs to cool patients. Their lowered temperatures were maintained for 12 hours after admission, and active rewarming started at 18 hours. This study of 67 patients found that 49 percent of its hypothermia group survived, as compared with only 42 percent of the unchilled control group.
The Circulation article’s authors endorsed the October 2002 recommendations of the International Liaison Committee on Resuscitation, which said, “Unconscious adult patients with spontaneous circulation after out-of-hospital cardiac arrest should be cooled to 32 degrees Celsius to 34 degrees Celsius for 12 to 24 hours when the initial rhythm was ventricular fibrillation (VF).”
Beiser, an assistant professor of emergency medicine at Chicago, is conducting animal studies to try to understand how hypothermia protects patients. The research could yield lifesaving — and potentially lucrative — results. “We’re looking at pharmaceuticals that mimic hypothermia,” he said.
Most people understand the danger to the oxygen-starved brain when the heart stops pumping blood, but many other secondary injuries also occur when circulation stops. “We’re beginning to understand how the secondary injury occurs and how to limit it,” Beiser said. “When you restart the heart and blood goes back to previously blood-starved tissue, you create a lot of oxidants, which can damage the tissue or transmit signals (that) can trigger cell death and inflammation.”
Patients revived from cardiac arrest sometimes suffer something called total body inflammation, which may stop capillaries from working and obstruct blood flow to vital organs, he said.
Hypothermia modulates this secondary injury, increasing certain oxidants and decreasing others, Beiser said, but exactly how is not well understood. For a long time, scientists thought it had to do with reduced energy needs. “The initial hypothesis with cooling is that we’re decreasing the metabolic rate of the body,” Beiser said.
“What we’re actually finding is it’s turning up the transcription of certain genes while turning down the transcription of other genes,” he said, referring to the genetic activity involved in the production of new proteins within cells.
One might expect emergency physicians would rush to embrace the use of therapeutic hypothermia, given the robust research in support of its use, but that hasn’t been the case. In the February 2005 issue of the journal Resuscitation, Abella, Chicago’s Terry Vanden Hoek and others reported that a survey of 265 physicians had found 87 percent said they were not using the technique.
“Among reasons cited for non-use, 49 percent felt that there were not enough data, 32 percent mentioned lack of incorporation of hypothermia into advanced cardiovascular life support (ACLS) protocols, and 28 percent felt that cooling methods were technically too difficult or too slow,” the report said.
Another reason may be that many doctors believe that there is little that can be done for cardiac arrests.
“There’s a culture of despair and a feeling of futility in these cases,” said Beiser, who adds that he makes sure to let his ER staff know about successful outcomes from hypothermia treatment to instill a sense of optimism.
“This culture of hope really helps get hypothermia off the ground in an institution.”
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