Annually, an estimated 295,000 people in the U.S. experience out-of-hospital cardiac arrest, and only 6 to 10 percent survive (Circ 2011;123:e18-e209). Another 200,000 hospitalized patients suffer cardiac arrest each year, with only 25 percent surviving to discharge (Crit Care Med 2011, online). These overall survival statistics have seemed mired in the low digits for decades. But strengthening the American Heart Association (AHA) Emergency Cardiovascular Care's "chain of survival" may lead to improvements in outcomes for both out-of-hospital and inpatient cardiac arrest victims.
Last year, the chain of survival became longer if not immediately stronger when the AHA updated its Cardiopulmonary Resuscitation (CPR) and Emergency Cardiovascular Care guidelines (Circulation 2010;122:S640-S933). The previous guidelines listed four series of events as crucial to cardiac arrest survival: an emergency response, CPR, defibrillation and advanced cardiac life support. Recent studies that showed promising results from the use of therapeutic hypothermia (TH) prompted the committee to add integrated care after resuscitation to the chain. Early indications suggest that the fifth link could tip survival rates in patients' favor.
A prompt response, continuous CPR
Survival rates for patients with out-of-hospital cardiac arrest vary widely, depending on circumstances, particularly emergency medical service (EMS) systems and hospitals. One key factor is whether the event is witnessed, followed by a prompt response. For instance, Valenzuela et al reported one of the highest survival to discharge rates—53 percent—among patients who experienced cardiac arrest at a casino and were treated by security personnel trained in CPR and the use of automated external defibrillators (N Engl J Med 2000;343:1206-1209). The authors attributed the high survival rate in part to the events occurring in a public area with surveillance cameras.
But only about 20 percent of cardiac arrests occur in public settings, making rapid response by EMS personnel more difficult, especially when the patient is in a hard-to-reach location such as an elevator, says Ian G. Stiell, MD, chair of emergency medicine research at the Ottawa Hospital Research Institute in Ontario, Canada. In a large-scale cluster-randomized study, Stiell and colleagues in the Resuscitation Outcomes Consortium (ROC) found that EMS personnel failed to follow the study's protocol duration of CPR in 36 percent of the patients, despite training.
The findings reflect the complex clinical circumstances that EMS face, the researchers wrote. ROC currently is testing in the real-world setting, which is fast paced and sometimes chaotic, Stiell says. "This is not a laboratory."
The 2010 guidelines emphasized early CPR and rapid defibrillation, but they don't resolve conflicting results in studies that, on one side, support a brief period of CPR followed by first analysis of cardiac rhythm, and on the other, call for prolonged CPR before first analysis.
Stiell and his ROC colleagues designed their study to try to clarify the issue. The trial enrolled 9,933 patients assigned to either early analysis in which EMS administered CPR for 30 to 60 seconds before first analysis of cardiac rhythm, or later-analysis, with CPR administration lasting three minutes before first cardiac rhythm analysis.
The researchers found no advantage in the longer duration group: 5.9 percent of patients survived to hospital discharge with satisfactory functional status in both groups. Patients with a first rhythm of ventricular tachycardia or ventricular fibrillation who first were given CPR by a bystander had poorer survival if they were in the later-analysis group.
"There is no point in performing a lot of additional CPR," Stiell insists. "For resuscitation, CPR should be started immediately and should be continued with minimal interruptions."
On the surface, the ROC's findings of a 5.9 percent survival rate reinforced the gloomy forecast for cardiac arrests. But the study included a wealth of measurements that ROC investigators are analyzing to identify practices that improve survival outcomes. "This is a major issue for the pre-hospital part of this equation," Stiell says. "We're learning a lot of what's right and wrong and how to correct it."
In-hospital cardiac arrests
Location counts most when it comes to in-hospital cardiac arrests, according to research by Demetrios J. Kutsogiannis, MD, of the division of critical care