Importance: Neurologically intact survival after out-of-hospital cardiac arrest (OHCA) has been increasing in Japan. However, associations between increased prehospital care, including bystander interventions and increases in survival, have not been well estimated.

Objective: To estimate the associations between bystander interventions and changes in neurologically intact survival among patients with OHCA in Japan.

Design, setting, and participants: Retrospective descriptive study using data from Japan's nationwide OHCA registry, which started in January 2005. The registry includes all patients with OHCA transported to the hospital by emergency medical services (EMS) and recorded patients' characteristics, prehospital interventions, and outcomes. Participants were 167,912 patients with bystander-witnessed OHCA of presumed cardiac origin in the registry between January 2005 and December 2012.

Exposures: Prehospital interventions by bystander, including defibrillation using public-access automated external defibrillators and chest compression.

Main outcomes and measures: Neurologically intact survival was defined as Glasgow-Pittsburgh cerebral performance category score 1 or 2 and overall performance category scores 1 or 2 at 1 month or at discharge. The association between the interventions and neurologically intact survival was evaluated.

Results: From 2005 to 2012, the number of bystander-witnessed OHCAs of presumed cardiac origin increased from 17,882 (14.0 per 100,000 persons [95% CI, 13.8-14.2]) to 23,797 (18.7 per 100,000 persons [95% CI, 18.4-18.9]), and neurologically intact survival increased from 587 cases (age-adjusted proportion, 3.3% [95% CI, 3.0%-3.5%]) to 1710 cases (8.2% [95% CI, 7.8%-8.6%]). The rates of bystander chest compression increased from 38.6% to 50.9%, bystander-only defibrillation increased from 0.1% to 2.3%, bystander defibrillation combined with EMS defibrillation increased from 0.1% to 1.4%, and EMS-only defibrillation decreased from 26.6% to 23.5%. Performance of bystander chest compression, compared with no bystander chest compression, was associated with increased neurologically intact survival (8.4% [6594 survivors/78,592 cases] vs 4.1% [3595 survivors/88,720 cases]; odds ratio [OR], 1.52 [95% CI, 1.45-1.60]). Compared with EMS-only defibrillation (15.0% [6445 survivors/42,916 cases]), bystander-only defibrillation (40.7% [931 survivors/2287 cases]) was associated with increased neurologically intact survival (OR, 2.24 [95% CI, 1.93-2.61]), as was combined bystander and EMS defibrillation (30.5% [444 survivors/1456 cases]; OR, 1.50 [95% CI, 1.31-1.71]), whereas no defibrillation (2.0% [2369 survivors/120,653 cases]) was associated with reduced survival (OR, 0.43 [95% CI, 0.39-0.48]).

Conclusions and relevance: In Japan, between 2005 and 2012, the rates of bystander chest compression and bystander defibrillation increased and were associated with increased odds of neurologically intact survival.