title: Impact of cardiopulmonary resuscitation duration on survival from paramedic witnessed out-of-hospital cardiac arrests: An observational study.
abstract: BACKGROUND
  Resuscitation guidelines often recommend ongoing cardiopulmonary resuscitation (CPR) efforts to hospital for out-of-hospital cardiac arrests (OHCA) witnessed by emergency medical service (EMS) personnel. In this study, we examine the relationship between EMS CPR duration and survival to hospital discharge in EMS witnessed OHCA patients.
  
  
  METHODS
  Between January 2003 and December 2011, 1035 adult EMS witnessed arrests of presumed cardiac aetiology were included from the Victorian Ambulance Cardiac Arrest Registry. CPR duration was defined as the total sum of prehospital CPR time in minutes. Adjusted logistic regression analyses were used to assess the impact of EMS CPR duration on survival to hospital discharge.
  
  
  RESULTS
  382 (37.3%) patients were discharged alive. The median CPR duration was 12 min (95% CI: 11-13) overall, but was higher in non-survivors compared to survivors (24 min vs. 2 min, p<0.001). The 99th percentile CPR duration in patients surviving to hospital discharge differed by the initial rhythm of arrest: 32 min (95% CI: 27-44) overall, 32 min (95% CI: 23-44) for ventricular fibrillation and pulseless ventricular tachycardia (VF/VT), 34 min (95% CI: 30-34) for pulseless electrical activity (PEA), and 28 min (95% CI: 21-28) for asystole. There were no survivors after 44 min for all rhythms. After adjusting for prehospital confounders, every minute increase in CPR duration was associated with a 13% reduction in the odds of survival to hospital discharge (OR 0.87, 95% CI: 0.84-0.89, p<0.001). The multivariable model predicted no chance of survival at or after a CPR duration of 48 min for VF/VT patients, 47 min for PEA patients and 45 min for asystole patients.
  
  
  CONCLUSIONS
  Resuscitation efforts exceeding 32 min yielded less than 1% of survivors from EMS witnessed OHCA. On the basis of this data, EMS witnessed OHCA patients may benefit from ongoing CPR efforts up to 48 min in duration.
authors.affiliation: Department of Research and Evaluation, Ambulance Victoria, Blackburn North, Victoria, Australia; Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Monash University, Prahran, Victoria, Australia. Electronic address: ziad.nehme@ambulance.vic.gov.au.
authors.forename: Z
authors.initials: Z
authors.lastname: Nehme
authors.affiliation: Department of Research and Evaluation, Ambulance Victoria, Blackburn North, Victoria, Australia; Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Monash University, Prahran, Victoria, Australia.
authors.forename: E
authors.initials: E
authors.lastname: Andrew
authors.affiliation: Department of Research and Evaluation, Ambulance Victoria, Blackburn North, Victoria, Australia; Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Monash University, Prahran, Victoria, Australia; Intensive Care Unit, Alfred Hospital, Prahran, Victoria, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Bernard
authors.affiliation: Department of Research and Evaluation, Ambulance Victoria, Blackburn North, Victoria, Australia; Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Monash University, Prahran, Victoria, Australia; Discipline of Emergency Medicine, School of Primary, Aboriginal and Rural Health Care, University of Western Australia, Crawley, Western Australia, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Smith
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000488:Allied Health Personnel; D001315:Australia; D016887:Cardiopulmonary Resuscitation / Q000379:methods* / Q000706:statistics & numerical data; D004632:Emergency Medical Services / Q000706:statistics & numerical data; D004634:Emergency Medical Technicians; D005260:Female; D006323:Heart Arrest; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D058687:Out-of-Hospital Cardiac Arrest / Q000401:mortality*; D010351:Patient Discharge / Q000706:statistics & numerical data; D012042:Registries; D015996:Survival Rate; D013997:Time Factors
keywords: Cardiac arrest; Cardiopulmonary resuscitation; Emergency medical services