CPR studies find no benefit to mouth-to-mouth over chest compressions alone
Thursday, July 29, 2010
For anyone trying to save a victim of cardiac arrest, the questions used to be: How many breaths do I give? How many chest compressions? And do I really want to do this in the first place?
New research published Thursday, however, adds to growing evidence that cardiopulmonary resuscitation could be far simpler and less off-putting. For adults in cardiac arrest, mouth-to-mouth breathing might not be needed -- or even helpful.
Two studies in which telephone dispatchers instructed bystanders how to perform CPR found that patients who got only chest compressions were as likely to survive as ones getting conventional CPR that included rescue breathing.
About one-quarter of people who collapse away from a hospital get CPR before paramedics arrive, which roughly doubles their chance of survival. The fraction of bystanders too squeamish to begin CPR because of mouth-to-mouth contact isn't known. But researchers are betting it's high.
"There is inherent appeal to chest compressions alone because of the challenges of doing the rescue breathing," said Thomas D. Rea, a physician at the University of Washington, in Seattle, where one of the studies was done. "If we can simplify the approach, I think we may enable more laypeople to perform CPR in a cardiac arrest."
The American Heart Association, which trained 13 million people in CPR last year, is developing new guidelines for resuscitation that will be released in October. The current guidelines encourage bystanders to at least do chest compressions, also known as hands-only CPR.
"To me, these studies are a win for hands-only CPR," said Michael R. Sayre, a physician at the Ohio State University Medical Center who chairs the 100-member committee of experts preparing the new protocols. "I'm confident that the guidelines will help get more people to at least do chest compressions."
Several experts said, however, that rescue breathing is essential for children in cardiac arrest, and for people who have suffocated or drowned. That's because in them breathing stops before the heart, and restoring respiration might be enough to bring them back to life.
But in adults with cardiac arrest, rescue breathing might not be necessary because when the heart stops suddenly (usually as the result of an abnormal rhythm), the lungs are inflated with oxygen-rich air. Pumping on the chest moves blood through the lungs, where it picks up that oxygen, and delivers it to the heart and brain, which need it most.
The prevailing theory is that not interrupting chest compressions with rescue breaths might ultimately deliver more oxygen than standard CPR in the crucial seven or eight minutes before paramedics arrive.
"Our hypothesis was that chest-compressions-only would produce better survival," Rea said.
Both studies, published Thursday in the New England Journal of Medicine, found a trend in that direction.
In one of the experiments, EMS dispatchers in two Washington cities (Seattle and Olympia) and London randomly assigned bystanders willing to be instructed over the phone to do hands-only or standard CPR on about 1,900 people in cardiac arrest. In the hands-only group, 12.5 percent of patients survived to leave the hospital, compared with 11 percent in the standard CPR group.
In the other experiment, the Swedish EMS system randomly assigned about 1,300 victims of cardiac arrest to the two alternatives. In the hands-only group, 8.7 percent of people survived at least 30 days, compared with 7 percent of those getting conventional CPR.
Those statistics, however, mask a far more complicated reality.
There is good evidence that victims of cardiac arrest fall into two groups -- one group harmed by rescue breathing and one group helped by it. The first group is far larger than the second, which is why eliminating rescue breathing makes little difference overall.
In the Washington State-London study, 70 percent of victims had a "cardiac" cause for their cardiac arrest -- usually a heart attack or angina attack. Those people probably had a lungful of air to call upon at the start of CPR.
On the other hand, 30 percent had a "non-cardiac" cause for their arrest -- a drug overdose, a choking episode, a weakness of the chest muscles. Their breathing had slowed down, depleting lungs and blood of oxygen, before their hearts stopped.
In people with a cardiac cause, 15 percent getting only chest compressions survived, compared with 11 percent who got standard CPR. In the people with non-cardiac causes, however, the trend was in the other direction. Fewer survived (5 percent) if they got only chest compressions than if they got standard CPR (7 percent).
Is it possible to distinguish the two groups in the field?
"The published evidence is that the EMS personnel usually can't tell," said Sayre, the physician leading the rewrite of the CPR guidelines.
When it comes to rescue breathing, "we are not ready to throw it out," said Myron L. Weisfeldt, a cardiologist and CPR researcher at Johns Hopkins University School of Medicine, who wrote an editorial in the journal.
Nevertheless, it appears increasingly clear that in adults who collapse without a pulse, doing only chest compressions might be doing a lot.