In this clinical trial planning grant, 15 PECARN children's hospitals with intensive care units retrospectively reviewed medical records of patients between 1 day and 18 years of age who sustained a cardiac arrest with return of spontaneous circulation in either the outpatient or inpatient setting. Characterization of this population included arrest specific events and etiology, patient characteristics, hospital course, interventions received hospital survival, and neurologic outcome. This information was used to create inclusion and exclusion criteria, and to calculate sample size requirements for the ongoing Therapeutic Hypothermia after Pediatric Cardiac Arrest (THAPCA) randomized controlled trial of hypothermia following pediatric cardiac arrest.