title: Helicopter transport improves survival following injury in the absence of a time-saving advantage.
abstract: BACKGROUND
  Although survival benefits have been shown at the population level, it remains unclear what drives the outcome benefits for helicopter emergency medical services (HEMS) in trauma. Although speed is often cited as the vital factor of HEMS, we hypothesized a survival benefit would exist in the absence of a time savings over ground emergency medical services (GEMS). The objective was to examine the association of survival with HEMS compared with GEMS transport across similar prehospital transport times.
  
  
  METHODS
  We used a retrospective cohort of scene HEMS and GEMS transports in the National Trauma Databank (2007-2012). Propensity score matching was used to match HEMS and GEMS subjects on the likelihood of HEMS transport. Subjects were stratified by prehospital transport times in 5-minute increments. Conditional logistic regression determined the association of HEMS with survival across prehospital transport times strata controlling for confounders. Transport distance was estimated from prehospital transport times and average HEMS/GEMS transport speeds.
  
  
  RESULTS
  There were 155,691 HEMS/GEMS pairs matched. HEMS had a survival benefit over GEMS for prehospital transport times between 6 and 30 minutes. This benefit ranged from a 46% increase in odds of survival between 26 and 30 minutes (adjusted odds ratio [AOR], 1.46; 95% CI, 1.11-1.93; P < .01) to an 80% increase in odds of survival between 16 and 20 minutes (AOR, 1.80; 95% CI, 1.51-2.14; P < .01). This prehospital transport times window corresponds to estimated transport distance between 14.3 and 71.3 miles for HEMS and 3.3 and 16.6 miles for GEMS.
  
  
  CONCLUSIONS
  When stratified by prehospital transport times, HEMS had a survival benefit concentrated in a window between 6 and 30 minutes. Because there was no time-savings advantage for HEMS, these findings may reflect care delivered by HEMS providers.
authors.affiliation: Division of General Surgery and Trauma, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Brown
authors.affiliation: Division of Acute Care Surgery, Department of Surgery, University of Rochester Medical Center, Rochester, NY.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Gestring
authors.affiliation: Department of Emergency Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA.
authors.forename: Francis X
authors.initials: FX
authors.lastname: Guyette
authors.affiliation: Division of General Surgery and Trauma, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Rosengart
authors.affiliation: Division of Acute Care Surgery, Department of Surgery, University of Rochester Medical Center, Rochester, NY.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Stassen
authors.affiliation: Division of General Surgery and Trauma, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA.
authors.forename: Raquel M
authors.initials: RM
authors.lastname: Forsythe
authors.affiliation: Division of General Surgery and Trauma, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA.
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Billiar
authors.affiliation: Division of General Surgery and Trauma, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Peitzman
authors.affiliation: Division of General Surgery and Trauma, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA. Electronic address: sperryjl@upmc.edu.
authors.forename: Jason L
authors.initials: JL
authors.lastname: Sperry
mesh_terms: D017732:Air Ambulances / Q000706:statistics & numerical data*; D000552:Ambulances / Q000706:statistics & numerical data; D015331:Cohort Studies; D004632:Emergency Medical Services / Q000379:methods; D005260:Female; D006801:Humans; D015601:Injury Severity Score; D016015:Logistic Models; D008297:Male; D009104:Multiple Trauma / Q000175:diagnosis / Q000401:mortality* / Q000628:therapy*; D016017:Odds Ratio; D057216:Propensity Score; D058996:Quality Improvement; D012189:Retrospective Studies; D018570:Risk Assessment; D016019:Survival Analysis; D013997:Time Factors; D061665:Time-to-Treatment; D014187:Transportation of Patients / Q000379:methods*