title: Lack of association between prehospital response times and patient outcomes.
abstract: BACKGROUND
  Limited data exist that examine the relationship between prehospital response times (RTs) and improved patient outcomes. Objective. We tested the hypothesis that patient outcomes do not differ substantially based on an explicitly chosen advanced life support (ALS) RT upper limit of 10 minutes 59 seconds (10:59 minutes).
  
  
  METHODS
  This case-control retrospective study was conducted in a metropolitan county with a population of 750,000 for the calendar year 2004. The emergency medical services (EMS) system is a single-tiered, ALS paramedic service that includes basic life support (BLS) first responders. The 90% fractile RT specification required by contractual agreement is 10:59 minutes or less for emergency, life-threatening (Priority 1) calls. Cases (study patients), defined as Priority 1 transports with RTs exceeding 10:59 minutes, were compared with controls, which comprised a random sample of Priority 1 calls with RTs of 10:59 minutes or less. Prehospital run reports and hospital outcomes were evaluated using explicit criteria by one observer for the primary outcome of in-hospital death and secondary outcomes of critical interventions performed in the field. We tested the hypothesis of equivalence using the 95% confidence intervals (CIs) for difference in proportions with alpha = 0.05 and beta = 0.2 to show Delta = +/- 5%.
  
  
  RESULTS
  Of the 3,270 emergency transports in 2004, we identified 373 study patients (RT > 10:59 min) and a random sample of 373 controls (RT < or = 10:59 min). Survival to hospital discharge was 80% (76% to 84%) for study patients vs. 82% (77% to 85%) for controls, yielding a 95% CI for the difference of -6 to +4%. ALS procedures were performed in 47.7% (95% CI: 43% to 53%) of study patients vs. 45.4% (40% to 51%) of controls (95% difference in proportions -10 to +5%). The most frequently performed procedures were administration of nitroglycerine and endotracheal intubation.
  
  
  CONCLUSIONS
  Compared with patients who wait 10:59 minutes or less for ALS response, Priority 1 patients who wait longer than 10:59 minutes could experience between a 6% increase and a 4% decrease in mortality, and do not have an increase in critical procedures performed in the field. Our data are most consistent with the inference that neither the mortality nor the frequency of critical procedural interventions varies substantially based on this prespecified ALS RT.
authors.affiliation: Department of Emergency Medicine, Carolinas Medical Center, Charlotte, North Carolina 28232-2861, USA. tom.blackwell@carolinashealthcare.org
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Blackwell
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Kline
authors.forename: J Jeffrey
authors.initials: JJ
authors.lastname: Willis
authors.forename: G Monroe
authors.initials: GM
authors.lastname: Hicks
mesh_terms: D000328:Adult; D000368:Aged; D017598:Efficiency, Organizational; D004632:Emergency Medical Services; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D012189:Retrospective Studies; D013997:Time Factors