Cardiopulmonary resuscitation that consists of only pressing on the chest works about as well and saves as many lives as conventional CPR incorporating both chest compressions and mouth-to-mouth breathing, according to new research.

The findings of two studies in which phone dispatchers instructed bystanders in how to perform CPR suggest that current techniques can be made simpler and less objectionable without harming most patients.

Currently, 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 initiate 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 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 lay people to perform CPR in a cardiac arrests."

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 Ohio State University Medical Center physician Michael Sayre, who leads 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 those cases, breathing stops first, and restoring respiration may be enough to bring them back to life.

But in adults with cardiac arrest, rescue breathing may 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.

CPR research on dogs suggests that the concentration of oxygen in the blood remains normal for about four minutes when only chest compressions are performed.

The prevailing theory is that not interrupting chest compressions with rescue breaths may 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," Dr. Rea said.

Both studies, published today in the New England Journal of Medicine, saw a trend in that direction, although in neither case was it large enough to reach statistical significance.

In one of the experiments, EMS dispatchers in two Washington cities (Seattle and Olympia) and in 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.

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