Prehospital factors associated with return of spontaneous circulation after nonshockable out-of-hospital cardiac arrest: a retrospective analysis of the Polk County Fire Rescue CARES registry

BACKGROUND: Non-shockable out-of-hospital cardiac arrest (OHCA), including pulseless electrical activity (PEA) and asystole, is associated with poor outcomes. Identifying prehospital factors associated with return of spontaneous circulation (ROSC) may inform emergency medical services (EMS) quality-improvement priorities. METHODS: We performed a retrospective analysis of a Polk County Fire Rescue Cardiac Arrest Registry to Enhance Survival (CARES) export. Patients whose first monitored rhythm was PEA or asystole were included. Outcomes were any documented ROSC and sustained ROSC through the end of EMS care. Unadjusted comparisons were followed by complete-case multivariable logistic regression evaluating age, sex, witnessed status, initial rhythm, epinephrine administration, time to first CPR, field hypothermia care, and AED application before EMS arrival. RESULTS: Among 1,198 included patients, median age was 66 years (interquartile range [IQR], 53-78), 59.8% were male, 20.9% had PEA, and 79.1% had asystole. Any ROSC occurred in 166 patients (13.9%), and 146 (12.2%) had sustained ROSC. In complete-case models (n=893), witnessed arrest, PEA rather than asystole, field hypothermia care, and female sex were associated with both outcomes. For any ROSC, adjusted odds ratios (aORs) were 2.65 (95% CI, 1.80-3.90) for witnessed arrest, 1.90 (95% CI, 1.29-2.79) for PEA, 1.99 (95% CI, 1.37-2.90) for field hypothermia care, and 0.60 (95% CI, 0.42-0.86) for male sex. Shorter time to first CPR was additionally associated with sustained ROSC (aOR per minute, 0.989; 95% CI, 0.979-0.999). AED use was not associated with either outcome. Epinephrine was not associated with any ROSC after adjustment and was inversely associated with sustained ROSC. CONCLUSIONS: Witnessed arrest and PEA were the most consistent positive correlates of ROSC in this county registry. Earlier CPR was associated with sustained ROSC. Associations involving epinephrine and field hypothermia care should not be interpreted as treatment effects because of likely time-dependent confounding and selection bias.