Effect of awareness time interval for out-of-hospital cardiac arrest on outcomes: A nationwide observational study

Purpose: Awareness of out-of-hospital cardiac arrest (OHCA) is critically important for bystanders to receive early instruction of dispatch-assisted cardiopulmonary resuscitation (DA-CPR) as well as to call for ambulance services. This study aimed to determine the association between awareness time interval and outcomes. Methods: EMS-treated, witnessed, adult (>18 years old) OCHAs with presumed cardiac etiology between 2012 and 2017 were analyzed, excluding patients with unknown awareness time factors and outcomes. The main exposure was awareness time interval (ATI), defined as the time from the witnessed event to calling for ambulance. Patients were categorized into five groups according to ATI: Group 1 (0-1 min), Group 2 (2-3 min), Group 3 (4-5 min), Group 4 (6-30 min) and Group 5 (31-60 min). The primary outcome was good neurological recovery defined as cerebral performance category 1 or 2 (good CPC). Multivariable logistic regression analysis was performed to calculate adjusted odds ratios (AORs) and 95% confidence intervals (Cls) for outcomes by ATI group (reference= Group 1) and by one-minute delay. We compared the effect size of ATI on outcomes across three witness groups (Layperson, Family, and Unknown). Results: A total of 36,809 OHCAs were analyzed. The AOR (95% CI) by one-minute ATI delay was 0.91 (0.90-0.92) for good CPC. The AORs (95% Cls) for outcomes compared with Group 1 were 0.98 (0.88-1.09) for Group 2, 0.64 (0.56-0.74) for Group 3, 0.30 (0.26-0.35) for Group 4, and 0.10 (0.05-0.20) for Group 5. In the Family bystander group, AORs (95% Cls) compared with Group 1 were significantly decreased by delay of ATI; 1.04 (0.88-1.11) for Group 2, 0.63 (0.81-0.83) for Group 3, and 0.31 (0.31-0.40) for Group 4 and 5. In Layperson-witnessed OHCAs, however, the AORs were significantly higher in the delayed awareness groups (Group 2 and Group 3). Conclusion: A longer ATI in witnessed adult OHCAs was associated with poor neurological recovery. A one-minute delay in ATI was associated with a 9% decrease of good neurological recovery, and the effect was significantly increased in Family-witnessed OHCAs.