Increasing Duration of Chest Compressions During CPR May Lead to Better Survival for Patients in Cardiac Arrest
By Deborah Brauser
Medscape Medical News
September 18, 2009 — Increasing the time that rescuers spend on chest compressions while performing cardiopulmonary resuscitation (CPR) could lead to increased survival in patients in cardiac arrest, according to results of an observational cohort study reported online September 14 in Circulation.
"Survival from out-of-hospital cardiac arrest is variable and often less than 5%," write Jim Christenson, MD, clinical professor of emergency medicine at the University of British Columbia in Vancouver, and colleagues.
Although chest compression fraction (CCF, the proportion of time spent performing chest compressions) is a vital part of quality CPR, interruptions during the compressions are common. However, animal studies have shown that these interruptions "decrease coronary and cerebral blood flow, which results in worse survival outcomes," report the study authors.
For this study, the investigators sought to estimate the independent effect of CCF on survival to hospital discharge in patients with out-of-hospital ventricular fibrillation or pulseless ventricular tachycardia.
They examined data from the Resuscitation Outcomes Consortium Cardiac Arrest Epistry, a group of 11 clinical centers with separate emergency medical service (EMS) agencies in the United States and Canada, formed to study out-of-hospital therapies for cardiac arrest and traumatic injury. A total of 506 patients (mean age, 64 years; 80% men) were enrolled from 7 sites and 78 agencies. All patients had confirmed ventricular fibrillation or ventricular tachycardia prior to EMS arrival between December 2005 and March 2007.
In addition, 34% arrested in a public location, 71% were witnessed by bystanders, and 51% received bystander CPR. The presence and frequency of chest compressions for each patient were measured with automated external defibrillators.
Overall, 117 of the patients (23%) survived to hospital discharge.
A return to spontaneous circulation was achieved 58% of the time when the CCF was 0% to 20%, 73% when the CCF was 21% to 40%, 76% when the CCF was 41% to 60%, 73% when the CCF was 61% to 80%, and 79% when the CCF was 81% to 100%.
Survival to hospital discharge occurred in 12% of the patients when the CCF was 0% to 20%, and increased to 22.9% when the CCF was 21% to 40%, 24.8% when the CCF was 41% to 60%, and 28.7% when the CCF was 61% to 80%. However, it dropped slightly, to 25%, when the CCF was 81% to 100%.
The authors explain that this slight drop, which they call "a curious finding," was likely due to the small sample size and wide confidence limits. Another possibility is "a true plateau effect of [CCF] above 80%."
The estimated adjusted linear effect on the odds ratio of survival for a 10% change in CCF was 1.11 (95% confidence interval, 1.01?- 1.21).
Limitations of the study include the observational study design, which allowed only an association between CCF and survival rather than a causal relation, and the fact that the majority of the cases were contributed by the 2 sites with a pre-existing ability to analyze electrocardiogram recordings.
"These data suggest that increasing [CCF] is an effective approach to improving outcomes from sudden cardiac arrest," write the study authors. "This observation is important and provides a rationale for relatively simple changes to resuscitation training and practice that are likely to improve survival if implemented."
They add, however, that many questions remain unanswered. "The optimal level of [CCF] that defines a practice goal for [EMS] training and quality improvement?.?.?. cannot be established by the present study," write the authors.
Dr. Christenson said in a press release, that "the chest compressions you do on a loved one are one of the most important things that can be done. Even by themselves, chest compressions can make a difference."
The Research Outcomes Consortium is supported by a series of cooperative agreements from the National Heart, Lung, and Blood Institute in partnership with the National Institute of Neurological Disorders and Stroke, US Army Medical Research & Material Command, the Canadian Institutes of Health Research-Institute of Circulatory and Respiratory Health, Defense Research and Development Canada, the Heart and Stroke Foundation of Canada, and the American Heart Association.
The study authors have disclosed no relevant financial relationships.
Circulation. Published online before print September 14, 2009.
