BRAIN-SAVING TREATMENT AFTER CARDIAC ARREST COULD HARM HEART
COLUMBUS, Ohio -- An experimental treatment that quickly re-establishes blood flow to the brain after resuscitation from cardiac arrest could in fact be harmful to the heart, according to a recent study.
In experiments with pigs, scientists at Ohio State University found that the treatment -- inducing high blood pressure after resuscitation from cardiac arrest by administering a higher-than-normal dose of the hormone norepinephrine -- increases the heart's oxygen use.
"The increased oxygen use is of concern," said Mark Angelos, assistant professor of emergency medicine at Ohio State and lead author of the study.
"Norepinephrine makes the heart work harder -- that is, it utilizes a higher than normal percentage of the oxygen being delivered to it. It's more efficient, but it may be more stressful to the heart. This treatment comes at a time when the heart is just coming out of cardiac arrest and is not working well."
"A little bit of norepinephrine is good to preserve blood
flow, but you can't push that too far without possibly having to pay a price within the heart," he said.
Currently, physicians use norepinephrine with post-cardiac arrest patients as a way to re-establish normal blood pressure.
"Administering norepinephrine to raise blood pressure above normal is still experimental," Angelos said. As a result, he said, it's being tested only on animals.
Angelos conducted the study with Kevin R. Ward, clinical assistant professor of emergency medicine, and Philip D. Beckley, assistant professor of allied medical professions, both from Ohio State. The group's work was published in a recent issue of the Annals of Emergency Medicine.
For their study, Angelos and his colleagues treated 10 pigs that were resuscitated after 16 minutes of cardiac arrest. Because their hearts closely resemble those of humans, pigs are often used in cardiac research. Five pigs were given a dose of norepinephrine that would result in normal blood pressure; the other five were given a higher norepinephrine dose to induce high blood pressure. At five and 15 minutes after resuscitation, the scientists measured the animals' blood flow to the heart, blood flow to the brain, and their hearts' oxygen use.
_ At 15 minutes after resuscitation, the animals in the high blood pressure group had almost three times the blood flow to the heart than the animals in the normal blood pressure group.
_ Heart oxygen use was also significantly higher among the high blood pressure animals. Among the normal blood pressure animals, myocardial oxygen use was about 14 percent; in the high blood pressure group, it was approximately 46 percent.
_ Somewhat surprisingly, at both five and 15 minutes after resuscitation, blood flow to the brain among the high blood pressure animals was no better than that of the normal blood pressure ones. This suggests that increasing blood flow to the brain after cardiac arrest may require an even higher dose of norepinephrine -- a dose that could have serious effects on the heart, Angelos said.
These results are of concern, Angelos said.
"In other recent studies, the higher dose norepinephrine treatment looked very favorable in terms of preserving blood flow to the brain after cardiac arrest and improving neurologic outcome," he said. "But no one looked at what it might do to the heart."
However, Angelos said, because these results are preliminary, research into this experimental treatment should continue.
"It still remains unclear at what point norepinephrine-induced high blood pressure to increase blood flow to the brain adversely affects the heart," he said. "There's a lot more work to be done."
Also, with continued research, the gains for cardiac arrest patients could be enormous, Angelos said.
"The period after resuscitation from cardiac arrest is critical," he said. "During that time, the brain may need higher-than-normal blood flow. Even after the pulse is back and the heart is beating, a person may still suffer ongoing brain damage because the brain is just not getting the blood it needs. That's the problem we think could be addressed by agents like norepinephrine."
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Contact: Mark Angelos, (614) 293-4760
Written by Kelly Kershner, (614) 292-8308