Two CPR strategies intended to improve patient survival after out-of-hospital cardiac arrest were found to have no significant effect in two related randomized clinical trials published in the Sept. 1 issue of the New England Journal of Medicine.
In the first study by the Resuscitation Outcomes Consortium (ROC), a "priming the pump" approach entailing a 3-minute period of chest compressions before the first analysis of cardiac rhythm and defibrillation produced the same rate of survival as did a briefer (30- to 60-second) period of manual chest compressions before cardiac rhythm analysis. Thus, extending CPR before defibrillation in the hope of increasing myocardial perfusion failed to improve patient outcomes.
In the second study, also by the ROC researchers, use of an impedance threshold device (ITD) to enhance venous return and cardiac output during CPR also produced the same rate of survival with satisfactory functional status, as did standard CPR without an ITD. Thus, use of the device also failed to improve patient outcomes.
These findings are particularly discouraging because the survival rate in the United States and Canada after out-of-hospital cardiac arrest "has been stagnant at 7.6% for more than 30 years," said Dr. Arthur B. Sanders of the department of emergency medicine at the University of Arizona’s Sarver Heart Center, Tucson.
The first ROC study was undertaken because despite several small studies of the issue, it was still unclear whether the traditional CPR approach of delivering defibrillatory shocks as soon as possible was inferior to the newer recommendation that EMS personnel should administer at least 2 minutes of CPR before delivering the shocks. In theory, "a few minutes of chest compression may increase myocardial perfusion, thus improving the metabolic state of the cardiac myocytes and enhancing the likelihood of successful defibrillation," said Dr. Ian G. Stiell of the department of emergency medicine and the Ottawa Hospital Research Institute, University of Ottawa, and his associates in the ROC.
They compared the two strategies by randomly assigning 9,933 adults treated by 150 EMS agencies in the United States and Canada to undergo either early (5,290 subjects) or delayed (4,643 subjects) defibrillation after nontraumatic cardiac arrest. The primary outcome measure was survival to hospital discharge with satisfactory functional status.
An identical 5.9% of subjects in each of the study groups survived to discharge with satisfactory status. There also were no differences between the two groups in several subgroup analyses, including survival to hospital admission, survival to hospital discharge regardless of functional status, and return of spontaneous circulation by arrival at the emergency department.
"Overall our data suggest that the administration of 2 minutes of CPR by EMS personnel before the first analysis of [cardiac] rhythm, which was suggested in the 2005 guidelines of the AHA-ILCOR [American Heart Association–International Liaison Committee on Resuscitation], is unlikely to provide a greater benefit than CPR of shorter duration," Dr. Stiell and his colleagues said (N. Engl. J. Med. 2011;365:787-97).
"The 2010 guidelines of the AHA-ILCOR give little direction as to the preferred period of CPR before analysis of cardiac rhythm. Each EMS system should consider its operational situation when deciding on its strategy for initial EMS-administered CPR," they added.
The second study was performed because no large randomized trial had yet addressed whether use of an ITD improved outcomes when compared with standard CPR, said Dr. Tom P. Aufderheide of the department of emergency medicine, Medical College of Wisconsin, Milwaukee.
The device is designed to increase the degree of negative intrathoracic pressure during CPR by preventing the passive inflow of air into the chest during chest recoil between compressions, without impeding active ventilation.
Animal studies showed that use of an ITD improved hemodynamics, perfusion of vital organs, and neurologically intact survival, and small, short-term clinical studies suggested that it increased systolic blood pressure during CPR and improved short-term survival. "The 2005 American Heart Association guidelines gave a class IIa recommendation for the use of the ITD to improve hemodynamic variables and the return of spontaneous circulation," Dr. Aufderheide and his colleagues in the ROC said.
They randomly assigned 8,718 adults with nontraumatic out-of-hospital cardiac arrest to undergo CPR with an ITD (4,373 subjects) or CPR with a sham ITD (4,345 subjects). As with the first ROC study, the primary outcome measure of this study was survival to hospital discharge with satisfactory functional status.
The rates of this outcome were 5.8% with the active ITD and 6.0% with the sham ITD, a nonsignificant difference, the researchers said (N. Engl. J. Med. 2011;365:798-806).
There also were no significant differences between the two study groups in secondary outcomes such as the return of spontaneous circulation by arrival at the emergency department, survival to hospital admission, or survival to hospital discharge regardless of functional status, they added.