For Dr. Sarah Perman, it is not enough for a cardiac arrest patient’s heart to work properly again. “What we care about is not just survival to when they’re discharged from the hospital,” she said, “but neurologic recovery at discharge.”
While a medical resident, Perman once cared for an elderly cardiac arrest patient. The attending team felt that the patient would have a grave prognosis. Their quick conclusion surprised Perman, who “started to learn that there was some generalized hesitancy” in treating cardiac arrest patients who have chronic heart conditions or do not initially respond to a defibrillator. The patient’s relatives still wanted the doctors to try everything they could, so they started therapeutic hypothermia, which was a success. After cooling the patient’s body temperature and a period of rewarming, the patient was revived and could go home.
Dr. Perman, now an assistant professor of emergency medicine at the University of Colorado, and her colleagues found that lowering the body’s internal temperature can help preserve neurological function for cardiac arrest patients with heart rhythms that do not respond to defibrillators. This controlled cooling is called therapeutic hypothermia, or TH, which is versatile enough to be carried out within ambulances and emergency rooms. Medical responders can cool the chest and limbs with ice packs or thread a catheter carrying cold saline through their patient.
Coauthor Dr. Benjamin Abella said most research and treatment effort has been placed on patients with shockable rhythms. With so little data on patients with nonshockable rhythms, hospitals are hesitant to use this therapy.
The American Heart Association estimates 530,000 individuals suffer cardiac arrest per year in the United States. For every minute a patient does not receive treatment, survival decreases by 7%.
“The human body has no real good mechanism to come back from a cardiac arrest,” said EMT Elizabeth Watkins. During cardiac arrest, the heart stops pumping blood and oxygen throughout the body. This is especially bad news for the brain, as cerebral fluid can also build up and put pressure on the brain. Death can result in minutes.
Defibrillators can restore shockable rhythms, while other rhythms are nonshockable and do not respond to electrical activity. Without treatment, survival chances for nonshockable patients are slim—as low as 10%.
TH can help preserve the neurobiology of comatose patients that have a pulse. This sort of corporeal refrigeration slows down the rate of cell death and acid build-up in the brain. Two landmark trials in 2002 endorsed TH for patients with shockable rhythms. This treatment, as Dr. Perman and her team found, could also benefit people who may not initially benefit from a defibrillator.
Drs. Perman and Abella’s team gathered data from 262 adult patients with non-shockable rhythms and paired them on characteristics such as age. “You have to make sure you’re comparing apples to apples,” Dr. Abella explained. Half of the patients had received TH, the other half did not.
The researchers were especially interested in how well neurologic function was preserved after TH, and so they then compared each patient’s recovery through a Cerebral Performance Category (CPC) test. This widely used clinical measurement describes level of consciousness on a scale of 1—someone who is stable and alert enough to go home—to 5—death. The researchers found that patients who received TH had 3.5 times better neurologic recovery (a CPC of “1” or “2”) compared to those who did not.
Drs. Perman and Abella’s study was published in Circulation. For Watkins, the EMT, a future study in TH effectiveness should examine patients who receive TH while they are in cardiac arrest. Starting TH sooner, rather than when patients regain a pulse, “decreases metabolic demand and causes less stress on the heart overall.” A drawback is that drugs typically given with cardiac arrest, like amiodarone, may not be as effective while going through a chilled body.
In order to understand how to better apply TH, Dr. Perman is looking to a bigger sample size. Thankfully, “there’s been a push for a national cardiac arrest database.” A September 2015 Institute of Medicine report outlined this is a major strategy to improve cardiac arrest survival.
“Cardiac arrest is a fairly grave occurrence and outcomes are not great, but we are doing everything we can to improve outcomes,” Dr. Perman said.