Doing CPR too fast can mean chest compressions aren't deep enough to get blood flowing to the heart and brain, a new study from Belgium suggests.
Researchers found that when rescuers pushed at a rate above 145 compressions per minute, the depth of those compressions dropped to less than four centimeters.
Recommendations from Europe and the United States now both call for compressions to be at least five centimeters (about two inches) deep, at a rate of 100 per minute or faster.
"The idea is that with each compression you move a little blood through the body and so if you go faster and deeper you might be moving more blood," said Dr. Benjamin Abella, an emergency medicine doctor at the Hospital of the University of Pennsylvania in Philadelphia, who wasn't involved in the new study.
But, "If you push faster, it stands to reason that you might end up pushing shallower," he told Reuters Health.
For bystanders who aren't professionally trained in CPR, short for cardiopulmonary resuscitation, the most important thing is just to push "deep and fast" - but not so fast that you're exhausted in a couple of minutes, researchers agreed. Then emergency medical services can provide more advanced care when they arrive.
For the new study, Dr. Koenraad Monsieurs from Antwerp University Hospital in Belgium and his colleagues used an accelerometer to measure chest compression rate and depth during CPR performed by healthcare professionals on 133 patients.
They found very fast compressions were often shallower than ones closer to a rate of 100 per minute. And at about 145 compressions per minute, depth got "unacceptably low," the researchers reported in Resuscitation.
That was according to 2005 European guidelines calling any compressions four centimeters or more deep enough. Since then, the standard has been raised.
"From my experience doing CPR… I had the impression that some rescuers would think, the faster the better," Monsieurs told Reuters Health. "It turns that for most rescuers, when they really go too fast the compression depth becomes insufficient."
That's important because deeper compressions increase the chance that using a defibrillator will get the heart going again and a patient will arrive at the hospital alive, researchers said. Deeper compressions send more blood to the heart and brain - the most important organs to keep alive, according to Monsieurs.
CPR is typically done after a heart attack or a near-drowning, when a person has no heart rate or isn't breathing.
In 2010, new American Heart Association guidelines said bystanders performing CPR can drop the rescue breaths that were part of the initial protocol and just go with chest compressions until EMS arrives.
Healthcare professionals can get speed and depth feedback from compression-measuring devices like accelerometers - but for bystanders the most important thing is just to do CPR in the first place, Abella said.
He said everyone should learn CPR however they can - whether or not they get officially certified - and shouldn't be afraid to jump in and start compressions in an emergency.
"If someone is in cardiac arrest, you can't hurt them, you can only help," he said.
One option is to try to push along to the Bee Gees 1977 disco song "Stayin' Alive," which happens to have a rhythm of 100 beats per minute. Of course, that beat might not be the easiest thing to remember in an emergency, Abella pointed out.
"As long as you're getting your hands on the chest and pushing hard and pushing fast, you're doing something that's very important," he said.