Circulation: During CPR, more compressions = more saved lives

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The chance that a person in cardiac arrest will survive increases when rescuers doing cardiopulmonary resuscitation (CPR) spend more time giving chest compressions, according to a multi-center study reported Sept. 14 in Circulation.

“Chest compressions move blood with oxygen to the heart and the brain to save the brain and prepare the heart to start up its own rhythm when a shock is delivered with a defibrillator," said lead study author Jim Christenson, MD, clinical professor of emergency medicine at the University of British Columbia in Vancouver. "We found that even short pauses in chest compressions were quite detrimental."

However, according to the authors, the proportion of time during CPR that rescuers spend giving chest compressions during each minute of CPR, called the chest compression fraction (CCF), is extremely variable.

Prior to 2005, interruptions to chest compressions resulted in less than 50 percent of total CPR time being spent on chest compressions. However, the 2005 American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care emphasized the importance of minimizing interruptions in chest compressions. This resulted in some emergency medical services (EMS) agencies achieving a CCF between 60 percent and 85 percent, Christenson said.

The researchers analyzed data from 78 EMS agencies in seven locations that were part of the Resuscitation Outcomes Consortium, a group of 11 regional clinical centers in Canada and the U.S. that study promising out-of-hospital therapies for cardiac arrest and traumatic injury. Automated external defibrillators measured the presence and frequency of chest compressions for each patient.

Patients were studied if they had a ventricular fibrillation or pulseless ventricular tachycardia cardiac arrest prior to EMS arrival between December 2005 and March 2007. In the 506 cases analyzed, the investigators found that a return to spontaneous circulation was achieved 58 percent of the time when the CCF was zero percent to 20 percent, and up to 79 percent when the CCF was 81 percent to 100 percent.

The authors noted the slight drop in survival in the group with the highest CCF rate was likely due to the small sample size of the study and wide confidence limits, although they acknowledge the possibility of a plateau effect when CCF is above 80 percent.

"There was roughly a 10 percent increase in the chance of survival for every 10 percent increase in the chest compression fraction," Christenson said.

More study is needed to identify the ideal CCF or to show when compressions are the most important, such as immediately before or after delivery of a shock, Christenson and colleagues concluded.