Extending the initial period of cardiopulmonary resuscitation (CPR) for out-of-hospital cardiac arrest patients did not improve survival outcomes, according to a study published Sept. 1 in the New England Journal of Medicine. The results of the large, cluster-randomized trial may help settle a debate about brief vs. prolonged CPR by paramedics before the first analysis of cardiac rhythm, and bring clarity to current guidelines.

“In the end, it is clear that taking extra time to do CPR before you analyze the rhythm is not helpful, and in some cases could be harmful,” lead author Ian G. Stiell, MD, said in an interview with Cardiovascular Business. Stiell, chair of emergency medicine research at the Ottawa Hospital Research Institute in Ottawa, was one of 27 authors who are members of the Resuscitation Outcomes Consortium (ROC) involved in the study.

Results from previous studies of paramedic-administered out-of-hospital CPR for cardiac arrest patients have been conflicting and guidelines modified in 2010 reflect that ambiguity. “The 2010 guidelines are very fuzzy, saying the evidence doesn’t tell us what to recommend,” Stiell said.

Stiell et al designed a large-scale cluster-randomized trial to compare strategies using a brief vs. a longer period of CPR followed by an initial analysis of rhythm for adults with out-of-hospital cardiac arrest. The study enrolled 9,933 patients seen by 150 Emergency Medical Service (EMS) agencies that participate in ROC, which includes 10 universities in the U.S. and Canada and their regional EMS systems. The primary outcome was survival to hospital discharge with satisfactory functional status.

The 10 ROC centers were divided into clusters that were randomly assigned one of two strategies: early analysis, in which EMS administered CPR for 30 to 60 seconds before first analysis of cardiac rhythm, and later-analysis, with CPR administration lasting three minutes before first cardiac rhythm analysis. Each cluster switched to the other strategy at least once during the study period, which was from June 2007 to November 2009.

The early-analysis group included 5,290 patients and the later-analysis group had 4,643 patients. In both groups, 5.9 percent of patients survived to hospital discharge with satisfactory functional status. Status was measured using the Rankin scoring system. The researchers found no significant differences in survival outcomes in subgroup analyses, and noted one scenario where extended CPR was a disadvantage.

“The chance of survival with satisfactory functional status did not improve with increasing time to the first analysis of cardiac rhythm, and among patients with an initial rhythm of ventricular tachycardia or ventricular fibrillation who received CPR from a bystander, the rate of survival tended to decline with increasing time to the first rhythm analysis,” Stiell and colleagues wrote.

Stiell said the authors did not go so far as to recommend changes to the guidelines but the results of their study likely will be taken into consideration in future modifications. “They will see there is no point in suggesting two to three minutes of additional CPR,” he said.

The authors wrote that the early-analysis strategy appeared more appropriate for patients who received CPR from a bystander before the arrival of EMS. They also provided guidance. “We believe that it is important to administer CPR for some period while the defibrillator pads are being applied and the compressions should be of high quality with minimal interruptions,” they wrote.   

Stiell added that the research effort created a large database of CPR measurements that will allow them to do further investigations, including 12 substudies already designed.

“This study took a lot of time and money,” he said. “We want to get the maximum yield out of it. Hopefully we will be providing a lot of useful information over the years on how to improve cardiac arrest survival.”