September 6, 2007 - A biomedical engineer at Purdue University has developed a new method to perform cardiopulmonary resuscitation that promises to be more effective than standard CPR, because it increases blood flow through the heart by 25 percent over the current method.
A new technique is needed because conventional CPR has a success rate of 5 percent to 10 percent, depending on how fast rescuers are able to respond and how well the procedure is performed. For every one minute of delay, the resuscitation rate decreases by 10 percent.
"In other words, at 10 minutes, the resuscitation is absolutely ineffective," said Leslie Geddes, Showalter distinguished professor emeritus in Purdue's Weldon School of Biomedical Engineering. "Any medical procedure that had that low a success rate would be abandoned right away. But the alternative is not very good, either: Don't do CPR and the person is going to die."
Geddes has developed the first new CPR alternative, called "only rhythmic abdominal compression," or OAC-CPR, which works by pushing on the abdomen instead of the chest.
"There are major problems with standard CPR," Geddes said. "One is the risk of breaking ribs if you push too hard, but if you don't push hard you won't save the person. Another problem is the risk of transferring infection with mouth-to-mouth breathing."
The new CPR method eliminates both risks, Geddes said.
Findings will be detailed in a research paper appearing this month in the American Journal of Emergency Medicine, published by Elsevier Inc. The paper was authored by Geddes and his Purdue colleagues Ann E. Rundell, assistant professor of biomedical engineering, biomedical engineering doctoral student Aaron Lottes, and basic medical sciences graduate students Andre Kemeny and Michael Otlewski.
In standard chest-compression CPR, which has been in practice since the 1960s, the rescuer pushes on the chest and blows into the subject's mouth twice for every 30 chest compressions. However, the risk of infection is so grave that many doctors and nurses often refuse to administer mouth-to-mouth resuscitation. In one 1993 study of 433 doctors and 152 nurses, 45 percent of doctors and 80 percent of nurses said they would refuse to administer mouth-to-mouth resuscitation on a stranger.
"This is the real world that nobody knows about, and it's a sobering thought," Geddes said.
OAC-CPR eliminates the need to perform mouth-to-mouth resuscitation.
The American Heart Association requires that rescuers administering CPR push with enough force to depress the chest 1.5 to 2 inches at a rate of 100 times per minute.
"To depress the chest 1.5 to 2 inches takes 100 to 125 pounds of force," Geddes said. "So you have to push pretty hard and pretty fast, and two people are needed to perform it properly. One blows up the lungs and the other compresses the chest. And when the one who's compressing the chest gets tired, they change positions."
OAC-CPR requires only one rescuer.
Instead of two breaths for every 30 chest compressions, the new procedure provides a breath for every abdominal compression because pushing on the abdomen depresses the diaphragm toward the head, expelling air from the lungs. The release of force causes inhalation.
Researchers have known since the 1980s that pushing on the abdomen circulates blood through the heart. The idea was originated by Purdue nursing doctoral student Sandra Ralston, Geddes said.
"She made the remarkable observation that if you pushed on the abdomen after each chest compression you could double the CPR blood flow," he said. "So I started thinking, what would happen if you just pushed on the abdomen and eliminated chest compression entirely?"
The procedure provides a new way to effectively perform "coronary perfusion," or pumping blood through the heart muscle, which is critical for successful resuscitation because the heart muscle is nourished by oxygenated blood, Geddes said.
Unfortunately, in standard chest-compression CPR, blood sometimes flows in the wrong direction, which means the coronary blood flow goes backward, bringing de-oxygenated blood back into the heart muscle," Geddes said. "This retrograde flow reduces the likelihood of resuscitation."
Findings showed that OAC-CPR eliminates this backward flow.
The Purdue researchers compared coronary artery blood flow during standard chest-compression CPR with the flow resulting from only abdominal compression CPR. Findings showed that using the new method and pushing with the same force recommended for standard CPR provided 25 percent more blood flow through the heart muscle without retrograde flow in the coronary arteries.
The researchers followed the standard recommended by the American Heart Association, pushing with 100 pounds of pressure 100 times per minute.
"With OAC-CPR, you really don't have to press as hard or as often, but we followed the American Heart Association standard to avoid possible criticism from people who could have said we didn't observe the standard," Geddes said.
Another benefit of OAC-CPR is that it eliminates rib fractures, which are commonly caused by compressing the chest. Rib fractures cause the chest to recoil more slowly, but effective CPR requires that rescuers wait until the chest recoils fully before compressing.
Geddes created a wooden "pressure applicator" that resembles a scaled-down version of a baseball home plate. It is contoured so that it can be used to compress the abdomen without pushing on the ribs. However, a rescuer could push with the hands to perform the procedure if no applicator were available.
Abdominal organs contain about 25 percent of the total blood volume in the body, and Geddes said that can be squeezed into the central circulation when you press on the abdomen.
Whether the procedure gains widespread acceptance depends on whether other researchers can duplicate the results.
For more information: www.reedelsevier.com