10 Case Definition CARES captures data on all non-traumatic out-of-hospital cardiac arrests where resuscitation is attempted by a 911 Responder (CPR and/or defibrillation). This also includes patients that receive an AED shock by a bystander prior to the arrival of 911 Responders. Inclusion and exclusion criteria are described below (Tables 1 and 2). Table 1. CARES inclusion criteria (all of the following) • Patients of all ages who experience a non-traumatic, out-of-hospital cardiac arrest. • Patients who are pulseless on arrival of 911 Responder; OR • Patients who become pulseless in the presence of 911 Responder; OR • Patients who have a pulse on arrival of EMS, where a successful attempt at defibrillation was undertaken by a bystander prior to arrival of 911 Responder. Table 2. CARES exclusion criteria (any of the following) • Unworked/untreated cardiac arrests, to include codes that are terminated immediately upon arrival of EMS because the patient is not a viable candidate for resuscitation due to: o Injuries incompatible with life. o The presence of rigor mortis or lividity. o Signs of decomposition. o Presence of a valid DNR. • Private EMS transport that did not involve 911 dispatch. • Cardiac arrest of clear and obvious traumatic etiology. • Bystander suspected cardiac arrest, where ROSC was achieved without the need for defibrillation or 911 Responder CPR. Data Collection & Elements Data collection within CARES is based on the Utstein- style definitions – a standardized template of uniform reporting guidelines for clinical variables and patient outcomes that was developed by international resuscitation experts 2,3 . The CARES web-based software (https://mycares.net), links three sources to describe each OHCA event: 1) 911 call center data, 2) EMS data, and 3) hospital data. Data can be submitted in two ways: using a data-entry form on the CARES website, or via daily upload from an agency’s electronic patient-care record (ePCR) system. Access to the CARES website is restricted to authorized users, who are prohibited from viewing data from another agency or hospital. Data elements collected from EMS providers include demographics (i.e. name, age, date of birth, incident address, sex, and race/ethnicity), arrest circumstances (i.e. location type of arrest, witness status, and presumed etiology), and resuscitation-specific data (i.e. information regarding bystander CPR initiation and/or AED application, defibrillation, initial arrest rhythm, return of spontaneous circulation [ROSC], field hypothermia, and pre-hospital survival status). EMS providers are also able to enter a number of optional elements, which further detail arrest interventions (i.e. usage of mechanical CPR device, ITD, 12 Lead, automated CPR feedback device, and advanced airway; administration of drugs; and diagnosis of STEMI). The CARES form includes a number of optional time elements, including estimated time of arrest, defibrillatory shock, and initial CPR. Supplemental data elements collected from the 911 call centers include the time that each 911 call was received, the time of dispatch for both first responder and EMS providers, and arrival time at the scene. Data elements collected from receiving hospitals include emergency department outcome, provision of therapeutic hypothermia, hospital outcome, discharge location, and neurological outcome at discharge (using the Cerebral Performance Categories [CPC] Scale). Receiving facilities may also complete optional elements outlining hospital procedures, including coronary angiography, CABG, and stent or ICD placement. The CARES dataset is geocoded on an annual basis, and linked to a number of census-tract level variables including: median household income, median age, race, unemployment rate, average household size, population density, and educational attainment.