title: Helicopter Emergency Medical Services save lives:  outcome in a cohort of 1073 polytraumatized patients.
abstract: BACKGROUND
  In many Western countries, Helicopter Emergency Medical Services (HEMS) have become standard in the prehospital care of severely injured patients. Several studies have shown that HEMS have a positive effect on patient's outcome, although it remains unclear which specific patients benefit most from its care. The aim of this study was to assess the effect of HEMS on the outcome of a large polytraumatized (Injury Severity Score≥16) population.
  
  
  METHODS
  All polytraumatized patients treated at the scene of the accident by EMS and/or HEMS and presented in the VU University Medical Center during a period of 6 years were included and retrospectively analyzed. The total population was divided into two groups according to the presence of HEMS on-scene. Prehospital, in-hospital, and outcome parameters were compared. The Trauma Injury Severity Score method was used to calculate the probability of survival.
  
  
  RESULTS
  Almost 60% of all included patients (n=1073) were treated only by an EMS crew on-scene. The remaining 446 patients received additional HEMS care. Significant differences between these two groups were observed in the demographic characteristics, showing that the HEMS group was more severely injured. The predicted survival was calculated using the Trauma Injury Severity Score method, as well as the observed survival, both showing a significantly higher outcome for the EMS group (0.88 vs. 0.66% and 87.7 vs. 71.3%). However, the Z-statistic showed a significant positive difference between the predicted and the observed survival for the HEMS group (P<0.005) and no significant differences for the EMS group (P>0.1), indicating that the chance of surviving in the HEMS group was higher. Per 100 HEMS dispatches, 5.4 additional lives were saved. A correlation of the observed survival with the first measured Revised Trauma Score on-scene showed a positive effect for the HEMS group when the Revised Trauma Score reached a value of 9 or lower.
  
  
  CONCLUSIONS
  On-scene HEMS care has a positive effect on the survival of polytraumatized patients, saving 5.4 additional lives per 100 HEMS deployments. This positive effect is especially observed in patients with abnormal vital signs (respiratory and hemodynamically). Research and revision of dispatch criteria are important to reach patients that benefit most from HEMS care.
authors.affiliation: Departments of Trauma Surgery, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Georgios F
authors.initials: GF
authors.lastname: Giannakopoulos
authors.forename: Mischka N
authors.initials: MN
authors.lastname: Kolodzinskyi
authors.forename: Herman M T
authors.initials: HM
authors.lastname: Christiaans
authors.forename: Christa
authors.initials: C
authors.lastname: Boer
authors.forename: Elly S M
authors.initials: ES
authors.lastname: de Lange-de Klerk
authors.forename: Wietse P
authors.initials: WP
authors.lastname: Zuidema
authors.forename: Frank W
authors.initials: FW
authors.lastname: Bloemers
authors.forename: Fred C
authors.initials: FC
authors.lastname: Bakker
mesh_terms: D017732:Air Ambulances / Q000706:statistics & numerical data*; D016009:Chi-Square Distribution; D015331:Cohort Studies; D016001:Confidence Intervals; D004632:Emergency Medical Services / Q000592:standards* / Q000639:trends; D005260:Female; D005392:First Aid / Q000379:methods; D015600:Glasgow Coma Scale; D006801:Humans; D015601:Injury Severity Score; D008297:Male; D009104:Multiple Trauma / Q000175:diagnosis / Q000401:mortality* / Q000628:therapy*; D009426:Netherlands; D061214:Patient Safety; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D016019:Survival Analysis; D017741:Survivors / Q000706:statistics & numerical data; D061665:Time-to-Treatment; D014193:Trauma Centers; D016896:Treatment Outcome; D014218:Triage