Association of Bystander Cardiopulmonary Resuscitation and Survival According to Ambulance Response-times after Out-of-Hospital Cardiac Arrest
Background—Bystander-initiated cardiopulmonary resuscitation (CPR) increases patient survival following out-of-hospital cardiac arrest (OHCA) but it is unknown to what degree bystander CPR remains positively associated with survival with increasing time to potential defibrillation. The main objective was to examine the association of bystander CPR with survival as time to advanced treatment increases.
Methods—We studied 7,623 OHCA patients between 2005-2011, identified through the nationwide Danish Cardiac Arrest Register. Multiple logistic regression analysis was used to examine the association between time from 911-call to emergency medical service arrival (response time) and survival according to whether bystander CPR was provided (yes/no). Reported are 30-day survival chances with 95% bootstrap confidence intervals.
Results—With increasing response times, adjusted 30-day survival chances decreased both for patients with bystander CPR and those without. However, the contrast between the survival chances of patients with vs. without bystander CPR increased over time: within 5 minutes, 30-day survival was 14.5% (95% CI: 12.8-16.4) vs. 6.3% (95% CI: 5.1-7.6), corresponding to 2.3 times higher chances of survival associated with bystander CPR; within 10 minutes, 30-day survival chances were 6.7% (95% CI: 5.4-8.1) vs. 2.2% (95% CI: 1.5-3.1), corresponding to 3.0 times higher chances of 30-day survival associated with bystander CPR. The contrast in 30-day survival became statistically insignificant when response time exceeded 13 minutes (bystander CPR vs. no bystander CPR: 3.7% [95% CI: 2.2-5.4] vs. 1.5% [95% CI: 0.6-2.7]) but 30-day survival was still 2.5 times higher associated with bystander CPR. Based on the model and Danish OHCA Statistics, an additional of 233 patients could potentially be saved annually if response time was reduced from 10 minutes to 5 minutes, and 119 patients if response time was reduced from 7 minutes (the median response time in this study) to 5 minutes.
Conclusions—The absolute survival associated with bystander CPR declined rapidly with time. Yet, bystander CPR while waiting for an ambulance was associated with a more than doubling of 30-day survival even in case of long ambulance response time. Decreasing ambulance response time by even a few minutes could potentially lead to many additional lives saved every year.
- Received July 7, 2016.
- Revision received September 27, 2016.
- Accepted October 11, 2016.