New CPR Method Shows Promise

WEST LAFAYETTE, Ind., Sept. 6 -- A new approach to cardiopulmonary resuscitation may improve the poor results of the life-saving procedure, according to researchers here.
In the new method, a rescuer presses on the abdomen, rather than the rib cage, according to Leslie Geddes, Ph.D., D.Sc., of Purdue University, and colleagues.
Because the abdominal organs contain about 25% of the body's blood supply, the abdominal pressure sharply increases the flow to the heart, compared with the flow from standard CPR, Dr. Geddes and colleagues reported in the September issue of the American Journal of Emergency Medicine.
"There are major problems with standard CPR," Dr. 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."
Dr. Geddes said a new method of CPR is needed because the standard method has a success rate of only 5% to 10%, depending on how fast rescuers respond and how well the procedure is performed.
For every minute of delay, he said, the resuscitation rate decreases by 10%. "In other words, at 10 minutes, the resuscitation is absolutely ineffective," Dr. Geddes noted.
The new method -- dubbed "only abdominal compression cardiopulmonary resuscitation," or OAC-CPR -- eliminates the risk of broken ribs, Dr. Geddes and colleagues noted.
But -- at least in experimental pigs -- it also increases blood flow to the heart during ventricular fibrillation by up to 60%, they said.
The researchers used a compression plate -- shaped roughly like a baseball home plate -- to compress the abdomens of pigs during an induced ventricular fibrillation. Repeated series of 30 abdominal compressions (100 lbs, at 100/min) were followed by two deep breaths.
They compared the resulting coronary perfusion to that seen when the heart was beating normally and to that seen during standard CPR.
To make the comparisons, they used a new measure -- called the coronary perfusion index, or CPI -- which was defined as the difference between aortic and right atrial pressures, summed over one minute.
Coronary perfusion then was defined as CPI/60, Dr. Geddes and colleagues noted.
In the normally beating pig heart, the CPI averaged 2,046 mm Hg. When OAC-CPR was performed, the CPI averaged 922 mm/Hg and the ratio was 0.24.
In other words, Dr. Geddes and colleagues said, OAC-CPR delivered 25% of the normal blood flow.
In a second series of experiments, using standard CPR, the comparable figures were 3,781 mm/Hg for the normally beating heart and 645 during CPR, for a ratio of 0.17.
When the researchers compared blood flow under the two forms of CPR, the average ratio was 1.60 -- or a 60% increase in blood flow using OAC-CPR, compared with standard CPR.
In standard CPR, the right atrial pressure sometimes exceeds the aortic pressure, leading to a backward flow of blood through the heart, Dr. Geddes said.
"This retrograde flow reduces the likelihood of resuscitation," he said.
On the other hand, in OAC-CPR aortic pressure was always higher than the right atrial pressure, eliminating the backward flow, he and colleagues found.
The research was supported by the Purdue Trask Fund. The researchers made no statement regarding potential conflicts. Primary source: American Journal of Emergency MedicineSource reference: Geddes LA et al. "A New CPR Method Employing Only Rhythmic Abdominal Compression: A preliminary report." Am J Emerg Med 2007;25(7):