title: Response time effectiveness: comparison of response time and survival in an urban emergency medical services system.
abstract: Emergency medical services (EMS) administrators seek methods to enhance system performance. One component scrutinized is the response time (RT) interval between call receipt and arrival on scene. While reducing RTs may improve survival, this remains speculative and unreported.
  
  
  OBJECTIVE
  To determine the effect of current RTs on survival in an urban EMS system.
  
  
  METHODS
  The study was conducted in a metropolitan county (population 620,000). The EMS system is a single-tier, paramedic service and provides all service requests. The 90% fractile RT specifications required for county compliance include 10:59 minutes for emergency life-threatening calls (priority I) and 12:59 minutes for emergency non-life-threatening calls (priority II). All emergency responses resulting in a priority I or priority II transport to a Level 1 trauma center emergency department over a six-month period were evaluated to determine the relation between specified and arbitrarily assigned RTs and survival.
  
  
  RESULTS
  Five thousand, four hundred twenty-four transports were reviewed. Of these, 71 patients did not survive (1.31%; 95% CI = 1.04% to 1.67%). No significant difference in median RTs between survivors (6.4 min) and nonsurvivors (6.8 min) was noted (p = 0.10). Further, there was no significant difference between observed and expected deaths (p = 0.14). However, mortality risk was 1.58% for patients whose RT exceeded 5 minutes, and 0.51% for those whose RT was under 5 minutes (p = 0.002). The mortality risk curve was generally flat over RT intervals exceeding 5 minutes.
  
  
  CONCLUSIONS
  In this observational study, emergency calls where RTs were less than 5 minutes were associated with improved survival when compared with calls where RTs exceeded 5 minutes. While variables other than time may be associated with this improved survival, there is little evidence in these data to suggest that changing this system's response time specifications to times less than current, but greater than 5 minutes, would have any beneficial effect on survival.
authors.affiliation: Center for Prehospital Medicine, Carolinas Medical Center, Charlotte, NC 28232-2861, USA. tom.blackwell@carolinashealthcare.org
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Blackwell
authors.forename: Jay S
authors.initials: JS
authors.lastname: Kaufman
mesh_terms: D004632:Emergency Medical Services / Q000592:standards* / Q000706:statistics & numerical data; D006302:Health Services Research; D006801:Humans; D012189:Retrospective Studies; D015996:Survival Rate; D013997:Time Factors; D014505:Urban Population