title: Timely bystander CPR improves outcomes despite longer EMS times.
abstract: OBJECTIVE
  This study aimed to determine the impact of bystander CPR on clinical outcomes in patients with increasing response time from collapse to EMS response.
  
  
  METHODS
  A population-based observational study was conducted in patients with witnessed out-of-hospital cardiac arrest (OHCA) of presumed cardiac etiology from 2012 to 2014. The time interval from collapse to CPR by EMS providers was categorized into quartile groups: fastest group (<4min), fast group (4 to <8min), late group (8 to <15min), and latest group (15 to <30min). The primary outcome was hospital discharge and the secondary outcome was survival with good neurological outcome. Multivariable logistic regression analysis was performed to evaluate the interaction between bystander CPR and the time interval from collapse to CPR by EMS providers.
  
  
  RESULTS
  A total of 15,354 OHCAs were analyzed. Bystander CPR was performed in 8591 (56.0%). Survival to hospital discharge occurred in 1632 (10.6%) and favorable neurological outcome in 996 (6.5%). In an interaction model of bystander CPR, compared to the fastest group, adjusted odds ratios (AORs) (95% CIs) for survival to discharge were 0.89 (0.66-1.20) in the fast group, 0.76 (0.57-1.02) in the late group, and 0.52 (0.37-0.73) in the latest group. For favorable neurological outcome, AORs were 1.12 (0.77-1.62) in the fast group, 0.90 (0.62-1.30) in the late group, 0.59 (0.38-0.91) in the latest group.
  
  
  CONCLUSIONS
  The survival from OHCA decreases as the ambulance response time increases. The increase in mortality and worsening neurologic outcomes appear to be mitigated in those patients who receive bystander CPR.
authors.affiliation: Department of Emergency Medicine, Seoul National University College of Medicine and Hospital, Seoul, Republic of Korea. Electronic address: pkj83531@naver.com.
authors.forename: Gwan Jin
authors.initials: GJ
authors.lastname: Park
authors.affiliation: Department of Emergency Medicine, Seoul National University College of Medicine and Hospital, Seoul, Republic of Korea. Electronic address: drsong@snu.ac.kr.
authors.forename: Kyoung Jun
authors.initials: KJ
authors.lastname: Song
authors.affiliation: Department of Emergency Medicine, Seoul National University College of Medicine and Hospital, Seoul, Republic of Korea. Electronic address: shinsangdo@medimail.co.kr.
authors.forename: Sang Do
authors.initials: SD
authors.lastname: Shin
authors.affiliation: Inje University Seoul Paik Hospital, Department of Emergency Medicine, Republic of Korea. Electronic address: cssurgeon@hanmail.net.
authors.forename: Kyung Won
authors.initials: KW
authors.lastname: Lee
authors.affiliation: Laboratory of Emergency Medical Services, Seoul National University Hospital Biomedical Research Institute, Seoul, Republic of Korea.
authors.forename: Ki Ok
authors.initials: KO
authors.lastname: Ahn
authors.affiliation: Department of Emergency Medicine, Seoul National University College of Medicine and Hospital, Seoul, Republic of Korea.
authors.forename: Eui Jung
authors.initials: EJ
authors.lastname: Lee
authors.affiliation: Department of Emergency Medicine, Seoul National University Boramae Medical Center, Seoul, Republic of Korea.
authors.forename: Ki Jeong
authors.initials: KJ
authors.lastname: Hong
authors.affiliation: Laboratory of Emergency Medical Services, Seoul National University Hospital Biomedical Research Institute, Seoul, Republic of Korea.
authors.forename: Young Sun
authors.initials: YS
authors.lastname: Ro
mesh_terms: D000328:Adult; D000368:Aged; D016887:Cardiopulmonary Resuscitation / Q000379:methods*; D003256:Community Participation / Q000706:statistics & numerical data*; D004632:Emergency Medical Services; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D058687:Out-of-Hospital Cardiac Arrest / Q000401:mortality / Q000628:therapy*; D011159:Population Surveillance; D012189:Retrospective Studies; D016019:Survival Analysis; D061665:Time-to-Treatment / Q000706:statistics & numerical data*; D016896:Treatment Outcome; D055815:Young Adult
keywords: Bystander cardiopulmonary resuscitation; Cardiac arrest; Emergency medical services; Outcomes