Researchers found that people whose hearts suddenly stopped beating more often had circulation come back in the ambulance if they were given adrenaline, also known as epinephrine. But those same patients were less likely to be alive and without brain damage a month after the cardiac arrest.

"The real thing that patients care about is not just getting to the emergency department with a heartbeat, but getting home intact," said Dr. Clifton Callaway, from the University of Pittsburgh, who wrote a commentary published with the study.

"You have greater success in getting the heart to start if you're giving epinephrine, but we're always concerned... there might be adverse consequences in other organ systems," such as the brain, he told Reuters Health.

According to the American Heart Association, more than 380,000 sudden cardiac arrests happen outside of the hospital every year in the United States.

In addition to CPR and sometimes electrical shocks, most of those patients are treated with adrenaline, which causes blood vessels not going to the heart to constrict, shunting as much blood as possible toward the heart.

For the new study, researchers led by Akihito Hagihara, from Kyushu University Graduate School of Medicine in Fukuoka, looked back on about 417,000 cases of cardiac arrest in which patients were treated by emergency medical services (EMS) and taken to the hospital between 2005 and 2008.

In mid-2006, Japanese laws changed to allow medics to give patients a shot of adrenaline if other methods including CPR failed to restart their hearts.

Just over 15,000 patients in cardiac arrest were given adrenaline during the study period.

According to EMS records, close to 19 percent of those patients had their circulation come back in the ambulance, compared to only six percent of cardiac arrest patients who weren't given in-transit adrenaline.

However, longer-term outcomes weren't as bright.

About five percent of patients survived a month after the cardiac arrest, whether or not they were given adrenaline. But when the researchers considered how long it took EMS to get patients to the hospital, whether they were given CPR by a bystander and other differences between patients, they found that people given adrenaline were less than half as likely to survive the arrest.

What's more, only about one-quarter of patients who were given an adrenaline shot and survived were still able to function pretty well on their own with limited neurological problems a month later, compared to close to half of those not treated with adrenaline in the ambulance.

"This finding implies that epinephrine administration might save the heart but not the brain," Hagihara's team wrote in the Journal of the American Medical Association on Tuesday.

NEED FOR DEFINITIVE EVIDENCE

The researchers note that they couldn't account for differences in how patients were treated once they arrived at the hospital, and it's possible some of those who weren't given adrenaline by EMS got a shot later.

Dr. Comilla Sasson, an emergency medicine doctor who has studied cardiac arrest at the University of Colorado School of Medicine in Aurora, said that was an important limitation to consider.

"There's so much more that happens, and I think it would be a little naïve to think that a one-time dose of epinephrine given during the resuscitation attempt could have that much of an impact on patient outcomes at one month," Sasson, who wasn't involved in the new study, told Reuters Health.

She also pointed out that the findings can't necessarily be extrapolated to patients in other countries. The Japanese patients typically got a single shot of adrenaline, she said, while in the U.S. it's standard for EMS to give doses every three to five minutes when trying to get a pulse back.

Callaway and Sasson agreed that the findings call for a more rigorous study in which cardiac arrest patients are randomly assigned to get adrenaline or not, then tracked for long-term outcomes. Only that type of trial can definitively pin any differences in survival and overall health on the adrenaline, itself.

The new finding "demands that we question our current practice," Callaway said.

SOURCE: Journal of the American Medical Association, online March 20, 2012.

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