Early versus Later Rhythm Analysis in Patients with Out-of-Hospital Cardiac Arrest. Part 2
The protocol was approved by the institutional review or research ethics boards at each participating site. The trial protocol, including the statistical analysis plan, is available at NEJM.org. All the authors vouch for the completeness and accuracy of the data and the analyses and for the fidelity of the study to the trial protocol.
Study Setting and Population
The trial was conducted at 150 of the 260 EMS agencies participating in the ROC. The trial agencies were selected because they had the capability to provide advanced cardiac life-support interventions and to record CPR process measures and because they met prespecified quality criteria during an initial run-in phase.
We included all persons 18 years of age or older who had an out-of-hospital cardiac arrest that was not the result of trauma and who were treated with defibrillation, delivery of chest compressions, or both by EMS providers. Persons were excluded if the arrest was witnessed by EMS personnel; if they had a blunt, penetrating, or burn-related injury; if the arrest was due to exsanguination; if they were pregnant; if they were prisoners; if they had an “opt-out” bracelet, indicating that they wished to opt out of the study; if they had “do not attempt resuscitation” orders; if the rhythm analysis was performed by police or a lay responder; or if they received initial treatment by an EMS agency that was not in the ROC. Patients were not required to provide informed consent; according to the regulations of the Food and Drug Administration and the Canadian Tri-Council agreement, this study qualified for exception from the requirements for informed consent because it involved research conducted during an emergency situation.
Randomization
Each of the 10 participating ROC centers (or sites) was divided into approximately 20 subunits, designated as “clusters,” according to EMS agency or geographic boundaries or according to defibrillator device, ambulance, station, or battalion. Randomization of clusters was stratified according to site. All episodes of cardiac arrest in a cluster were randomly assigned to one CPR strategy; after a set period of time, ranging from 3 to 12 months, all episodes in that cluster were then assigned to the other strategy. All the clusters were assigned to cross over to the other strategy one or more times during the study at fixed intervals; we estimated that approximately 100 patients would be included during each interval.
Study Intervention
Patients in the early-analysis group were assigned to receive 30 to 60 seconds of chest compressions and ventilations (sufficient time to place defibrillator electrodes) before electrocardiographic (ECG) analysis, and those in the late-analysis group were assigned to receive 3 minutes of chest compressions and ventilations before ECG analysis. The assigned intervention was implemented by the first qualified EMS provider to arrive at the scene (defibrillation-capable firefighter, emergency medical technician, or paramedic). The start and stop times for CPR were recorded by the responders, and the information was supplemented by the recording of defibrillator time.
The training of participating EMS providers emphasized uninterrupted chest compressions except for required ventilations, with compressions and ventilations applied in a 30:2 ratio, and specified that advanced airway devices were to be placed with minimal interruptions to compressions. Every 6 months, the EMS providers underwent some retraining that included written reminders, slide presentations, and Web-based modules. All ROC sites implemented high-quality electronic monitoring of the CPR process with the use of defibrillator hardware and software. Adherence to the protocol-specified performance targets and to the requirements for data submission was monitored throughout the study by a study monitoring committee, which provided regular feedback to sites.