Impact of Awareness Time Interval on the Effect of Bystander Cardiopulmonary Resuscitation on Out-of-Hospital Cardiac Arrest: A Nationwide Study

Purpose: The awareness time interval (ATI), the time from the witnessed event to emergency medical service (EMS) activation, is an important factor influencing out-of-hospital cardiac arrest (OHCA) outcomes. Since bystander cardiopulmonary resuscitation (BCPR) is provided after cardiac arrest is recognized, the effect of BCPR may vary depending on ATI delay. We aimed to investi-gate whether ATI modifies the effect of BCPR on OHCA outcomes. Materials and Methods: A population-based observational study was conducted with EMS-treated witnessed adult (>= 18 years) OHCAs between 2013 and 2018. The exposure variable was provision of BCPR. The primary outcome was a good neurological outcome defined as cerebral performance category scale 1or 2 (good CPC). Multivariable logistic regression analysis was con-ducted using the ATI group (-1, 1-5, 5- min) as the interaction term. Results: Of 34366 eligible OHCAs, 65.5% received BCPR. EMS was activated within 1 min in 45.9%, within 1-5 min in 29.2%, and after 5 min in 24.9% cases. In the adjusted interaction model, compared with no BCPR, a longer ATI resulted in smaller adjusted odds ratios for good CPC in the BCPR group [5.33 (4.17-6.82) for ATI <= 1 min, 5.14 (4.00-6.60) for 1-5 min, and 2.14 (1.63-2.81) for ATI >5 min]. Conclusion: The effect of BCPR on improving the chances for a good neurological outcome decreased as time from collapse to EMS activation increased. The importance of early recognition of OHCA and EMS activation should be emphasized in BCPR training.