Posted by UT Southwestern Medical Center on Sep 9th 2020
Shortening time between CPR and shocks improves cardiac-arrest survival
Shortening time between CPR and shocks improves cardiac-arrest survival
June 29, 2011 – Reducing the intervals between giving cardiopulmonary resuscitation (CPR) and an electronic defibrillator shock after cardiac arrest significantly improves survival, according to UT Southwestern Medical Center emergency medicine doctors involved in an international study.
Chest compressions applied within 10 seconds before the defibrillator shocks and within 20 seconds after the shock boosted survival chances by more than half compared to the rates for people who received chest compressions more than 20 seconds before or 40 seconds after the shock, according to findings reported in Circulation: Journal of the American Heart Association. The National Institutes of Health study is available online at http://circ.ahajournals.org
"We've been doing training in Dallas for two to three years to reduce the pauses between chest compressions and shocks to less than five seconds, and that has improved survival in the city about 60 percent," said Dr. Ahamed Idris, professor of emergency medicine and internal medicine at UT Southwestern and a pioneer in resuscitation research and cardiopulmonary resuscitation who was also a study co-author.
"This is really a very simple thing anyone can do to increase survival," noted Dr. Idris, director of the Dallas-Fort Worth Center for Resuscitation Research.
American Heart Association resuscitation guidelines advise minimizing interruptions to chest compressions to 10 seconds or less. Previous studies, however, hadn't measured how such pauses in CPR affected survival through discharge from the hospital.
U.S. emergency medical services annually treat nearly 300,000 cardiac arrest cases that occur outside the hospital, according to the study. Less than 8 percent survive.
UT Southwestern serves as the lead investigative site for the Dallas-Fort Worth arm of the Resuscitation Outcomes Consortium, which conducted the study. The consortium is a group of 11 U.S. and Canadian emergency medical services that carry out research on cardiac arrest resuscitation and life-threatening traumatic injury.
Uninterrupted chest-compressions key to survival in cardiac arrest outside hospital setting
Credit: UT Southwestern Medical Center
Maximizing the proportion of time spent performing chest compressions during cardiopulmonary resuscitation (CPR) substantially improves survival in patients who suffer cardiac arrest outside a hospital setting, according to a multicenter clinical study that included UT Southwestern Medical Center.
The findings, available in today's issue of Circulation, come from the largest clinical investigation to evaluate the association between chest compressions by emergency medical service (EMS) providers before the first attempted defibrillation and survival to hospital discharge. Out-of-hospital cardiac arrest is a leading cause of premature death worldwide, and survival is often less than 5 percent.
One of the most important aspects of quality CPR is the proportion of time spent performing chest compressions, but EMS providers typically perform chest compressions only 50 percent of the total time spent on resuscitative efforts.
"It's a common problem, because rescuers are involved in so many other tasks - checking for a pulse, starting intravenous therapy and giving ventilation, among other things," said Dr. Ahamed Idris, professor of emergency medicine at UT Southwestern and a pioneer in resuscitation research and CPR. Dr. Idris also is the principal investigator for the Dallas portion of the new study, conducted at seven clinical centers across North America.
"Compressions are being interrupted half of the time or more, and that has a detrimental effect on the survival of patients," Dr. Idris said. "This study reinforces that interrupting chest compressions has a bad effect on survival. It also provides a rationale for relatively simple changes to CPR training and practice, that if implemented are likely to improve survival."
Dallas-area paramedics and firefighters are being trained to begin CPR immediately and to administer uninterrupted chest compressions for two minutes before re-checking the heart rhythm or using a defibrillator to shock the heart. UT Southwestern's emergency medicine program provides medical oversight for EMS providers in more than a dozen Dallas-area cities.
In this study, researchers studied data from patients in the Resuscitation Outcomes Consortium (ROC) who had suffered from cardiac arrest with a heart rhythm indicating ventricular fibrillation or ventricular tachychardia. The researchers focused on the effect of the number of chest compressions paramedics administered per minute before they shocked the heart.
"People who received chest compressions 60 to 80 percent of the time during CPR did better than those who received fewer chest compressions," Dr. Idris said.
Previous animal studies have demonstrated that interruptions in chest compressions decrease coronary and cerebral blood flow. Based on further clinical and laboratory observations, the American Heart Association and the European Resuscitation Council Guidelines for Cardiopulmonary Resuscitation in 2005 recommended increasing the proportion of time spent delivering chest compressions.
In 2008 the American Heart Association updated its CPR guidelines and now advocates that bystanders only perform continuous chest compressions for cardiac arrest instead of combining chest compressions with mouth-to-mouth ventilation.
During CPR, more chest compressions mean more saved lives
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 in Circulation: Journal of the American Heart Association.
"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 Jim Christenson, M.D., lead author of the study and clinical professor of emergency medicine at the University of British Columbia. "We found that even short pauses in chest compressions were quite detrimental."
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 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.
Researchers analyzed data from 78 EMS agencies in seven locations that were part of the Resuscitation Outcomes Consortium (ROC), a group of 11 regional clinical centers in Canada and the United States that study promising out-of-hospital therapies for cardiac arrest and traumatic injury.
The study is the first to analyze CPR tracings in a large group of patients. 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.
Ventricular fibrillation or pulseless ventricular tachycardia are abnormal heart rhythms in which the heart's lower chambers contract erratically or extremely rapidly and pump little or no blood.
In the 506 cases analyzed, researchers found that a return to spontaneous circulation was achieved 58 percent of the time when the CCF was 0 percent to 20 percent, and up to 79 percent when the CCF was 81 percent to 100 percent.
Return of spontaneous circulation means that the heart begins pumping blood effectively on its own.
Survival to hospital discharge occurred in 12 percent of patients when CCF was 0 percent to 20 percent. It increased to nearly 29 percent when CCF was 61 percent to 81 percent, but dropped slightly to 25 percent when CCF was 81 percent to 100 percent CCF.
Researchers said 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 said.
"We should continue chest compressions as much as possible, only pausing to do things that are proven to be medically beneficial," he said.
For bystanders, the results emphasize the lifesaving potential of learning CPR and delivering chest compressions.
"The chest compressions you do on a loved one are one of the most important things that can be done," Christenson said. "If you feel rusty or are not confident giving mouth-to-mouth ventilation along with chest compressions then just do chest compressions. Even by themselves, chest compressions can make a difference."
More compressions, fewer interruptions lead to higher cardiac arrest survival
Survival rates from out-of-hospital sudden cardiac arrest almost doubled when professional rescuers using cardiopulmonary resuscitation (CPR) gave better chest compressions and minimized interruptions to them, according to research reported in Circulation: Journal of the American Heart Association.
"It's a back-to-basics message. Even with professional rescuers, starting IVs and delivering medications can take a back seat to good quality chest compressions," said Alex G. Garza, M.D., M.P.H., lead author of the study and associate professor of emergency medicine at the Washington Hospital Center and Georgetown University School of Medicine in Washington, D.C.
Garza's study tracked results from changes in resuscitation protocols implemented by the Kansas City Emergency Medical Services (EMS) in 2006. The Kansas City EMS put the highest priority on hands-on time to provide chest compressions with limited interruptions. Rescuers performed 50 chest compressions before pausing to provide two breaths. (American Heart Association guidelines call for 30 compressions followed by two breaths.) Other changes included the rescuers delaying intubating the patient and administering medications.
Overall survival from out-of-hospital cardiac arrest increased from 7.5 percent to 13.9 percent after the EMS department made the changes to its resuscitation practices.
Comparing the 36 months prior to the protocol shift with the 12 months afterwards, the researchers also found:
- Of patients whose cardiac arrest was witnessed by bystanders and who were initially in ventricular fibrillation, the success of resuscitation in restoring a heartbeat and getting the patient to the hospital alive improved from 37.8 percent (54 of 143) to 59.6 percent (34 of 57 patients).
- Of patients whose cardiac arrest was witnessed by bystanders and who were in ventricular fibrillation, survival to hospital discharge rose from 22.4 percent (32 of 143) to 43.9 percent (25 of 57).
- Of the 25 discharged patients, 88 percent scored well on measures of brain function.
"It takes five to seven chest compressions to raise the pressure enough to begin driving blood into the heart tissue," Garza said. "If you stop too often to provide a couple of breaths, then you haven't helped the heart much and you have to start building pressure all over again."
Nearly 300,000 sudden cardiac arrest (SCA) victims are treated by EMS in the United States each year, according to the American Heart Association. SCA is an abrupt loss of heart function; it usually occurs after the heart's electrical impulses become rapid or erratic, preventing the heart from effectively pumping blood.
"In that five- to 10-minute period after an SCA, a lot of evidence shows that if you do chest compressions to keep blood going to the heart muscle, defibrillation is far more likely to work," Garza said.