title: Helicopter emergency medical services for adults with major trauma.
abstract: BACKGROUND
  Although helicopters are presently an integral part of trauma systems in most developed nations, previous reviews and studies to date have raised questions about which groups of traumatically injured patients derive the greatest benefit.
  
  
  OBJECTIVE
  The purpose of this review is to determine if helicopter emergency medical services transport (HEMS) is associated with improved morbidity and mortality, compared to ground emergency medical services transport (GEMS), for adults with major trauma. The primary outcome was survival to hospital discharge. Secondary outcomes were quality-adjusted life years (QALYs) and disability-adjusted life years (DALYs).
  
  
  METHODS
  Searches were run in CENTRAL, MEDLINE, EMBASE, CINAHL (EBSCOhost), SCI-EXPANDED, CPCI-S, and ZETOC in January 2012. Relevant websites were also searched, including controlled trials registers, HSRProj, the World Health Organization (WHO) ICTRP, and OpenSIGLE. Searches were not restricted by date, language, or publication status. Attempts were made to contact authors in the case of missing data.
  
  
  METHODS
  Eligible trials included randomised controlled trials (RCTs) and non-randomised intervention studies. Non-randomised studies (NRS), including controlled trials and cohort studies, were also evaluated. Each study was required to have a GEMS comparison group. An injury severity score (ISS) > 15 or an equivalent marker for injury severity was required. Only adults aged 16 years or older were included.
  
  
  METHODS
  Three review authors independently extracted data and assessed the risk of bias of included studies. The Downs and Black quality assessment tool was applied for NRS. The results were analysed in a narrative review, and with studies grouped by methodology and injury type. A predefined subgroup was comprised of four additional studies that examined the role of HEMS versus GEMS for inter-facility transfer. Summary of findings tables were constructed in accordance with the GRADE Working Group criteria.
  
  
  RESULTS
  Twenty-five studies met the entry criteria for this review. Four additional studies met the criteria for a separate, predefined subgroup analysis of patients transferred to trauma centres by HEMS or GEMS. All studies were non-randomised studies; no RCTs were found. Survival at hospital discharge was the primary outcome. Data from 163,748 people from 21 of the 25 studies included in the primary analysis were available to calculate unadjusted mortality. Overall, considerable heterogeneity was observed and an accurate estimate of overall effect could not be determined. Based on the unadjusted mortality data from five trials that focused on traumatic brain injury, there was no decreased risk of death with HEMS (relative risk (RR) 1.02; 95% CI 0.85 to 1.23). Nine studies used multivariate regression to adjust for confounding, the five largest indicated a statistically significant increased odds of survival associated with HEMS. All Trauma-Related Injury Severity Score (TRISS)-based studies indicated improved survival in the HEMS group as compared to the Major Trauma Outcomes Study (MTOS) cohort; some studies showed survival benefits in both the HEMS and GEMS groups as compared to MTOS. No studies were found to evaluate the secondary outcome of morbidity as assessed by QALYs and DALYs. All four studies suggested a positive benefit when HEMS was used to transfer patients to higher level trauma centres. Overall, the quality of the included studies was very low as assessed by the GRADE Working Group criteria.
  
  
  CONCLUSIONS
  Due to the methodological weakness of the available literature, and the considerable heterogeneity of effects and study methodologies, an accurate composite estimate of the benefit of HEMS could not be determined. Although five of the nine multivariate regression studies indicated improved survival associated with HEMS, the remainder did not. All were subject to a low quality of evidence as assessed by the GRADE Working Group criteria due to their non-randomised design. Similarly, TRISS-based studies, which all demonstrated improved survival, cannot be considered strong evidence because of their methodology, which did not randomize the use of HEMS. The question of which elements of HEMS may be beneficial for patients has not been fully answered. The results from this review provide motivation for future work in this area. This includes an ongoing need for diligent reporting of research methods, which is imperative for transparency and to maximise the potential utility of results. Large, multicentre studies are warranted as these will help produce more robust estimates of treatment effects. Future work in this area should also examine the costs and safety of HEMS, since multiple contextual determinants must be considered when evaluating the effects of HEMS for adults with major trauma.
authors.affiliation: R. Adams Cowley Shock Trauma Center, University of Maryland, Baltimore, MD, USA. sgalvagno@anes.umm.edu.
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Galvagno
authors.forename: Stephen
authors.initials: S
authors.lastname: Thomas
authors.forename: Christopher
authors.initials: C
authors.lastname: Stephens
authors.forename: Elliott R
authors.initials: ER
authors.lastname: Haut
authors.forename: Jon M
authors.initials: JM
authors.lastname: Hirshon
authors.forename: Douglas
authors.initials: D
authors.lastname: Floccare
authors.forename: Peter
authors.initials: P
authors.lastname: Pronovost
mesh_terms: D000328:Adult; D017732:Air Ambulances; D004185:Disability Evaluation; D006801:Humans; D015601:Injury Severity Score; D019057:Quality-Adjusted Life Years; D012044:Regression Analysis; D016019:Survival Analysis; D014947:Wounds and Injuries / Q000150:complications / Q000401:mortality*