Study Population

We identified 62,931 adult patients (18 years of age or older) experiencing an index IHCA (defined as the first pulseless arrest during a hospitalization) at 390 GWTG-R participating hospitals between April 2006 and June 2010. We restricted the analysis cohort to patients entered in the database after April 2006, because postresuscitation Do Not Attempt Resuscitation (DNAR) data were not collected before this date. To arrive at a more consistent cohort of hospital inpatients, we excluded certain patients. We excluded 12,033 patients who were in perioperative areas (pre-, intra-, or postoperative), other procedural areas (such as the cardiac catheterization laboratory or interventional radiology), emergency departments, or rehabilitation areas, or who were missing event location data. Patients with implantable cardioverter-defibrillators were also excluded (846 patients). Patients with arrest duration of < 2 minutes without ROSC were considered partial or incomplete resuscitations and were excluded (397 patients). Patients with missing event context, sex, or arrest cause data or with missing or implausible event times were also excluded (2,498 patients). Approximately 5% of available records were excluded because of missing data. The final study cohort included 47,157 patients from 369 hospitals.