Abstract 33: Survival from Out-of-Hospital Cardiac Arrest Is Lowest at Night: Findings from the Cardiac Arrest Registry to Enhance Survival (CARES)

Abstract

Background: Understanding temporal variability in the incidence and outcomes of out-of-hospital cardiac arrest (OHCA) has important implications for pre-hospital resource planning and structuring systems for OHCA care. Methods: Using the Cardiac Arrest Registry to Enhance Survival (CARES) database, we studied patients with OHCA of presumed cardiac etiology who were treated by emergency medical services (EMS) from 10/2005 to 12/2010. Measures of pre-hospital care, survival to hospital discharge, and neurologic outcomes were compared between OHCA occurring during daytime (0701-1500h), evening (1501-2300h), and overnight (2301-0700h). Results: The frequency of OHCA varied significantly across time blocks with 7503 (40.4%) occurring during daytime, 6883 (37.0%) during evening, and 4202 (22.6%) occurring overnight (p<0.0001). Compared with OHCA patients during daytime or evening, those with OHCA overnight were more likely to be younger, arrest at home, have an unwitnessed arrest, have a non-shockable initial rhythm, and were less likely to receive bystander CPR or AED use (Table). Time from 911 call to EMS arrival was longest at night. Survival to hospital discharge was lowest among overnight OHCA patients. There was no difference in frequency of favorable neurologic outcomes among survivors in the different time blocks. After controlling for differences in patient and arrest characteristics, with daytime as the reference, overnight OHCA was associated with lower survival (OR 0.74, 95% CI 0.63-0.87, p=0.0002), with similar survival for patients with OHCA during evening (OR 0.99, 95% CI 0.88-1.12, p=0.91). Conclusion: There is temporal variability in OHCA occurrence with the nadir in frequency occurring at night. OHCA at night is independently associated with lowest survival to hospital discharge. Underlying patient, EMS system, and hospital factors contributing to these observed findings requires further exploration.