Background: We evaluated the association between survival and bystander cardiopulmonary resuscitation (CPR) with or without dispatcher instructions (DI) considering the time from emergency call receipt by the dispatch center to emergency medical services (EMS) personnel’s contact with the patient (i.e., time to EMS arrival).

Methods: This prospective study conducted in Osaka City, Japan, from 2009 to 2015 included patients with medical cause-related out-of-hospital cardiac arrest who were ≥18 years old. The primary outcome was one-month favorable neurological survival. Using multiple logistic regression models, the adjusted odds ratios (AOR) of independent and DI-dependent CPR for the primary outcome were compared with no CPR. Adjustments were made for patients’ age, sex, activities of daily living before the cardiac arrest, year of cardiac arrest, location, presence or absence of witnesses, etiology of cardiac arrest, and the time from EMS contact with the patient to patient’s arrival at the hospital. The effective estimated “time to EMS arrival” was also calculated.

Results: For analyses 10,925 individuals were eligible. Independent CPR had a significantly higher one-month favorable neurological survival than no CPR whereas there was no significant difference between DI-dependent CPR and no CPR (AOR, 1.90 [1.47–2.46] and 1.16 [0.91–1.47], respectively). The estimated “time to EMS arrival” for a one-month favorable neurological survival after independent CPR was ≤13 minutes.

Conclusions: Bystander CPR that did not need DI was associated with significantly higher one-month favorable neurological survival than no CPR, with an effective estimated “time to EMS arrival” of ≤13 minutes.

3 - Effectiveness of dispatcher instructions-dependent or independent bystander cardiopulmonary resuscitation on neurological survival among patients with out-of-hospital cardiac arrest