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Cost-Effectiveness of Helicopter Versus Ground Emergency Medical Services for Trauma Scene Transport in the United States

  • M. Kit Delgado
    Correspondence
    Address for correspondence: M. Kit Delgado, MD, MS
    Affiliations
    Department of Surgery, Division of Emergency Medicine, Stanford University School of Medicine, Palo Alto, CA

    Center for Health Policy and Center for Primary Care and Outcomes Research, Stanford University School of Medicine, Palo Alto, CA

    Stanford Investigators for Surgery, Trauma, and Emergency Medicine, Stanford University School of Medicine, Palo Alto, CA
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  • Kristan L. Staudenmayer
    Affiliations
    Department of Surgery, Division of General Surgery, Trauma/Critical Care Section, Stanford University School of Medicine, Palo Alto, CA

    Stanford Investigators for Surgery, Trauma, and Emergency Medicine, Stanford University School of Medicine, Palo Alto, CA
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  • N. Ewen Wang
    Affiliations
    Department of Surgery, Division of Emergency Medicine, Stanford University School of Medicine, Palo Alto, CA

    Center for Health Policy and Center for Primary Care and Outcomes Research, Stanford University School of Medicine, Palo Alto, CA

    Stanford Investigators for Surgery, Trauma, and Emergency Medicine, Stanford University School of Medicine, Palo Alto, CA
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  • David A. Spain
    Affiliations
    Department of Surgery, Division of General Surgery, Trauma/Critical Care Section, Stanford University School of Medicine, Palo Alto, CA

    Stanford Investigators for Surgery, Trauma, and Emergency Medicine, Stanford University School of Medicine, Palo Alto, CA
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  • Sharada Weir
    Affiliations
    University of Massachusetts School of Medicine, Center for Health Policy and Research, Worcester, MA
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  • Douglas K. Owens
    Affiliations
    Center for Health Policy and Center for Primary Care and Outcomes Research, Stanford University School of Medicine, Palo Alto, CA

    VA Palo Alto Health Care System, Palo Alto, CA
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  • Jeremy D. Goldhaber-Fiebert
    Affiliations
    Center for Health Policy and Center for Primary Care and Outcomes Research, Stanford University School of Medicine, Palo Alto, CA
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      Study objective

      We determine the minimum mortality reduction that helicopter emergency medical services (EMS) should provide relative to ground EMS for the scene transport of trauma victims to offset higher costs, inherent transport risks, and inevitable overtriage of patients with minor injury.

      Methods

      We developed a decision-analytic model to compare the costs and outcomes of helicopter versus ground EMS transport to a trauma center from a societal perspective during a patient's lifetime. We determined the mortality reduction needed to make helicopter transport cost less than $100,000 and $50,000 per quality-adjusted life-year gained compared with ground EMS. Model inputs were derived from the National Study on the Costs and Outcomes of Trauma, National Trauma Data Bank, Medicare reimbursements, and literature. We assessed robustness with probabilistic sensitivity analyses.

      Results

      Helicopter EMS must provide a minimum of a 15% relative risk reduction in mortality (1.3 lives saved/100 patients with the mean characteristics of the National Study on the Costs and Outcomes of Trauma cohort) to cost less than $100,000 per quality-adjusted life-year gained and a reduction of at least 30% (3.3 lives saved/100 patients) to cost less than $50,000 per quality-adjusted life-year. Helicopter EMS becomes more cost-effective with significant reductions in patients with minor injury who are triaged to air transport or if long-term disability outcomes are improved.

      Conclusion

      Helicopter EMS needs to provide at least a 15% mortality reduction or a measurable improvement in long-term disability to compare favorably with other interventions considered cost-effective. Given current evidence, it is not clear that helicopter EMS achieves this mortality or disability reduction. Reducing overtriage of patients with minor injury to helicopter EMS would improve its cost-effectiveness.
      SEE EDITORIAL, P. 365.

      Introduction

       Background

      Trauma is the leading cause of death for US residents aged 1 to 44 years, is the most common cause of years of life lost for those younger than 65 years,
      Centers for Disease Control and Prevention
      Web-based Injury Statistics Query and Reporting System (WISQARS) [online]. 2010. National Center for Injury Prevention and Control, Centers for Disease Control and Prevention (producer).
      and exacts $406 billion per year in costs, more than heart disease or cancer.
      • Finkelstein E.A.
      • Corso P.S.
      • Miller T.R.
      Incidence and Economic Burden of Injuries in the United States.
      • Kirschtein R.
      Disease-specific estimates of direct and indirect costs of illness and NIH support.
      Survival after trauma is improved by timely transport to a trauma center for severely injured patients.
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      Helicopter emergency medical services (EMS) offers faster transport than ground EMS for patients injured far from trauma centers and is considered a preferred means of transport for critically injured patients.
      • Moylan J.A.
      Impact of helicopters on trauma care and clinical results.
      Approximately 27% of US residents are dependent on helicopter transport to access Level I or II trauma center care within the “golden hour” from injury to emergency department (ED) arrival.
      • Branas C.C.
      • MacKenzie E.J.
      • Williams J.C.
      • et al.
      Access to trauma centers in the United States.
      However, there are conflicting data to support routine use for scene transport. Most studies have concluded that helicopter transport was associated with improved survival,
      • Baxt W.
      • Moody P.
      The impact of a rotorcraft aeromedical transport emergency care service on trauma mortality.
      • Moylan J.A.
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      Factors improving survival in multisystem trauma patients.
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      • Jacobs L.
      • Juda R.
      A comparison of ground paramedics and aeromedical treatment of severe blunt trauma patients.
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      Impact of emergency medical helicopter service on mortality for trauma in north-east Italy: a regional prospective audit.
      • Moront M.
      • Gotschall C.
      • Eichelberger M.
      Helicopter transport of injured children: system effectiveness and triage criteria.
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      • Rutledge R.
      • Baker C.C.
      • et al.
      A comparison of the association of helicopter and ground ambulance transport with the outcome of injury in trauma patients transported from the scene.
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      • Gabram S.
      • Sztajnkrycer M.
      • et al.
      Helicopter air medical transport: ten-year outcomes for trauma patients in a New England program.
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      • Yeomans K.
      The effect of air medical transport on survival after trauma in Johannesburg, South Africa.
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      • Harrison T.H.
      • Buras W.R.
      • et al.
      Helicopter transport and blunt trauma mortality: a multicenter trial.
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      • Davis D.P.
      • Ochs M.
      • et al.
      Air medical transport of severely head-injured patients undergoing paramedic rapid sequence intubation.
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      • et al.
      The impact of aeromedical response to patients with moderate to severe traumatic brain injury.
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      • et al.
      HEMS vs Ground-BLS care in traumatic cardiac arrest.
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      • Bankey P.E.
      • et al.
      Helicopters and the civilian trauma system: national utilization patterns demonstrate improved outcomes after traumatic injury.
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      • Tallon J.M.
      • Sealy B.
      Air versus ground transport of major trauma patients to a tertiary trauma centre: a province-wide comparison using TRISS analysis.
      • Sullivent E.E.
      • Faul M.
      • Wald M.M.
      Reduced mortality in injured adults transported by helicopter emergency medical services.
      • Stewart K.E.
      • Cowan L.D.
      • Thompson D.M.
      • et al.
      Association of direct helicopter versus ground transport and in–hospital mortality in trauma patients: a propensity score analysis.
      • Galvagno Jr, S.
      • Haut E.
      • Zafar S.
      • et al.
      Association between helicopter vs ground emergency medical services and survival for adults with major trauma.
      whereas others showed no difference.
      • Schiller W.
      • Knox R.
      • Zinnecker H.
      Effect of helicopter transport of trauma victims on survival in an urban trauma center.
      • Nicholl J.
      • Brazier J.
      • Ha S.
      Effects of London helicopter emergency medical services on survival after trauma.
      • Brathwaite C.
      • Rosko M.
      • McDowell R.
      A critical analysis of on-scene helicopter transport on survival in a statewide trauma system.
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      • Mileski W.
      • Wolf S.
      • et al.
      Impact of discontinuing a hospital-based air ambulance service on trauma patient outcomes.
      • Biewener A.
      • Aschenbrenner U.
      • Rammelt S.
      • et al.
      Impact of helicopter transport and hospital level on mortality of polytrauma patients.
      • Talving P.
      • Teixeira P.G.
      • Barmparas G.
      • et al.
      Helicopter evacuation of trauma victims in Los Angeles: does it improve survival?.
      • Bulger E.M.
      • Guffey D.
      • Guyette F.X.
      • et al.
      Impact of prehospital mode of transport after severe injury: a multicenter evaluation from the Resuscitation Outcomes Consortium.
      These studies have methodological limitations and selection bias, missing physiologic data, and heterogeneity in study settings and observational study designs.
      What is already known on this topic
      Helicopter emergency medical services (EMS) are expensive compared with ground transport. The cost-benefit in terms of improved survival in trauma has not been established.
      What question this study addressed
      This decision analysis investigated the mortality reduction needed to make the cost-effectiveness of helicopter EMS transport comparable to that of other health care activities. National Study on Costs and Outcomes of Trauma and other databases were used as inputs to the model.
      What this study adds to our knowledge
      Helicopter EMS must provide a substantial (15%) relative risk reduction (1.3 lives saved/100 patients) to cost less than $100,000 per quality-adjusted life-year gained. The effect on acute morbidity was not studied.
      How this is relevant to clinical practice
      To be cost-effective, helicopter EMS would have to reduce the number of patients with minor injury transported or demonstrate that there are improvements in long-term disability that improve the balance sheet.

       Importance

      In 2010, there were more than 69,700 helicopter transports for trauma to US Level I and II trauma centers; 44,700 (64%) were from the scene of injury.
      American College of Surgeons
      National Trauma Data Bank. Cited April 4, 2010.
      According to the Medicare Fee Schedule, insurance companies reimburse $5,000 to $6,000 more per transport than ground ambulance, which means $200 to $240 million more was spent with this modality for trauma scene transport in 2010.
      Centers for Medicare & Medicaid Services ambulance fee schedule
      Furthermore, a systematic review has shown than more than half of the patients flown have minor or non–life-threatening injuries that would likely have similar outcomes if transport were by ground.
      • Bledsoe B.E.
      • Wesley A.K.
      • Eckstein M.
      • et al.
      Helicopter scene transport of trauma patients with nonlife-threatening injuries: a meta-analysis.
      Helicopter transport also may present a safety risk. In 2008, medical helicopter crashes caused 29 fatalities, the highest number to date, provoking federal review of the safety of air medical transport.
      US Government Accountability Office (GAO)
      Aviation Safety: Potential Strategies to Address Air Ambulance Safety Concerns.
      Currently, there is little empirical guidance on whether the routine use of helicopter EMS for trauma scene transport represents a good investment of critical care resources.

       Goals of This Investigation

      Given the limitations of the helicopter EMS outcomes literature, we aimed to determine the minimum reduction in mortality or long-term disability provided by helicopter EMS for its routine use to be considered cost-effective over ground EMS for the transport of patients from the scene of injury to a trauma center. We assessed these clinical thresholds relative to current evidence about effectiveness of helicopter transport. In this study, we account for transport costs and safety, as well as the inevitable overtriage of patients with minor injuries to helicopter transport.

      Materials and Methods

       Study Design

      We developed a decision-analytic Markov model to compare the costs and outcomes of helicopter versus ground EMS trauma transport to a trauma center from a societal perspective during a patient lifetime. Clinical data and cost inputs were derived from the National Study on the Costs and Outcomes of Trauma (NSCOT),
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      • Mackenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.
      • et al.
      The National Study on Costs and Outcomes of Trauma.
      supplemented by the National Trauma Data Bank,
      American College of Surgeons
      National Trauma Data Bank. Cited April 4, 2010.
      Medicare reimbursements,
      Centers for Medicare & Medicaid Services ambulance fee schedule
      and the literature. We applied the model to a nationally representative population of trauma victims (aged 18 to 85 years) with a nationally representative distribution of injury severities (minor to unsurvivable). The model follows patients from injury through transport, their hospitalization and first year postdischarge, and during the rest of their lifetimes.
      The primary outcome was the threshold relative risk (RR) reduction in in-hospital mortality by helicopter EMS needed to achieve an incremental cost-effectiveness ratio compared with ground EMS below $100,000 per quality-adjusted life-year gained, a threshold at which health care interventions are generally considered cost-effective in high-income countries.
      • Eichler H.G.
      • Kong S.X.
      • Gerth W.C.
      • et al.
      Use of cost-effectiveness analysis in health-care resource allocation decision-making: how are cost-effectiveness thresholds expected to emerge?.
      Quality-adjusted life-years measure both quality and quantity of life lived after a health care intervention. We also evaluated the threshold RR reduction needed to achieve incremental cost-effectiveness ratio less than $50,000 per quality-adjusted life-year gained, a more conservative and widely cited threshold.
      • Grosse S.D.
      Assessing cost-effectiveness in healthcare: history of the $50,000 per QALY threshold.
      We assumed that the relative reduction in mortality from helicopter EMS would apply only to patients with serious injury, as defined by at least 1 injury with an Abbreviated Injury Score of 3 or greater.
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      • Davis D.P.
      • Peay J.
      • Serrano J.A.
      • et al.
      The impact of aeromedical response to patients with moderate to severe traumatic brain injury.
      • Galvagno Jr, S.
      • Haut E.
      • Zafar S.
      • et al.
      Association between helicopter vs ground emergency medical services and survival for adults with major trauma.
      • Bledsoe B.E.
      • Wesley A.K.
      • Eckstein M.
      • et al.
      Helicopter scene transport of trauma patients with nonlife-threatening injuries: a meta-analysis.
      The Abbreviated Injury Score is a validated measure of injury severity that is assigned according to hospital discharge diagnosis codes and is used to calculate the overall Injury Severity Score.
      • Baker S.P.
      • O'Neill B.
      • Haddon Jr, W.
      • et al.
      The Injury Severity Score: a method for describing patients with multiple injuries and evaluating emergency care.
      • Sacco W.J.
      • MacKenzie E.J.
      • Champion H.R.
      • et al.
      Comparison of alternative methods for assessing injury severity based on anatomic descriptors.
      We assessed the robustness of our estimates with 1-way and probabilistic sensitivity analyses of all model variables and adhered to the recommendations of the Panel on Cost-effectiveness in Health and Medicine.
      • Weinstein M.C.
      • Siegel J.E.
      • Gold M.R.
      • et al.
      Recommendations of the Panel on Cost-effectiveness in Health and Medicine.

       Model Assumptions

      The model represents a single decision about whether to use helicopter or ground ambulance transport in the field, followed by a series of consequences related to this decision (Figure 1). We assumed that differences in costs and outcomes between helicopter and ground EMS were driven by differences in inhospital survival (ie, survival to hospital discharge) for severely injured patients and in the probability of crashing en route to the hospital. Inhospital survival is the only outcome measured in virtually all helicopter EMS studies, primarily because of availability of data.
      Figure thumbnail gr1
      Figure 1Model structure. The model calculates the difference in the costs and outcomes related to the decision of choosing helicopter EMS as opposed to ground EMS for the scene transport of an injured patient to a US trauma center. Event probabilities and their associated costs conditional on strategy chosen (helicopter versus ground) and injury severity are presented in . A Markov model was used to calculate remaining patient life expectancy and lifetime health care expenditures for the cohort of patients who survive to be discharged from the hospital.
      The model accounted for variation in the clinical outcomes and costs based on whether patients had serious or minor injuries. Patients were determined to have had a serious injury if there was at least 1 injury with an Abbreviated Injury Score greater than 3 and minor injuries if they had no injury with an Abbreviated Injury Score greater than 3. The probabilities for whether a patient had minor or serious injuries were determined with data from the National Trauma Data Bank 2010 National Sample (Appendix E1, available online at http://www.annemergmed.com). The distinction of minor versus serious injuries was necessary to determine the overtriage rate. Helicopter EMS overtriage is defined as patients with minor injuries who are transported by helicopter EMS to trauma centers. These patients are not expected to have improved outcomes if transported by helicopter to a trauma center. In 2010, according to our analysis of the National Trauma Data Bank, the average national overtriage rate was 36%, but this rate varied greatly by center, from 9% to 69% (Table E1, available online at http://www.annemergmed.com). Patients transported by EMS with only minor injuries had an inhospital death rate of 1.3%.
      The distribution of population characteristics came from data obtained from the NSCOT, a multicenter prospective study of 5,191 patients with serious injury treated at trauma centers and nontrauma centers in the United States.
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      • Mackenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.
      • et al.
      The National Study on Costs and Outcomes of Trauma.
      Data were gathered from published studies, and additional primary cost data were provided by NSCOT investigators. NSCOT also contains data on inhospital and 1-year survival, costs, and quality of life, using the SF-6D instrument. According to published data from NSCOT, patients with serious injury have a mean inhospital mortality rate of 7.6%, with a range of 2.3% for patients with a maximum Abbreviated Injury Score of 3 to 30.2% for patients with a maximum Abbreviated Injury Score of 5 to 6. All model input assumptions are presented in Table 1.
      Table 1Model input assumptions.
      VariableBase-Case ValueRange for Sensitivity AnalysisReference
      Distribution of cohort characteristics
      Age, %, yN/AMacKenzie
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
       18–5472
       55–6411
       65–748
       75–859
      Male, %69N/AMacKenzie
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      Maximal AIS, %N/AMacKenzie,
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      NTDB 2010 analysis, Newgard
      • Newgard C.D.
      • Zive D.
      • Holmes J.F.
      • et al.
      A multisite assessment of the American College of Surgeons Committee on Trauma field triage decision scheme for identifying seriously injured children and adults.
      “Minor injury” subgroup
       AIS 1 (minor)10
       AIS 2 (moderate)26
      “Serious injury” subgroup
       AIS 3 (serious)39
       AIS 4 (severe)17
       AIS 5–6 (critical-unsurvivable)8
      Transport assumptions
      Mean distance traveled by helicopters for trauma scene transports in the United States, miles5525–85Brown,
      • Brown J.B.
      • Stassen N.A.
      • Bankey P.E.
      • et al.
      Helicopters and the civilian trauma system: national utilization patterns demonstrate improved outcomes after traumatic injury.
      Carr
      • Carr B.G.
      • Caplan J.M.
      • Pryor J.P.
      • et al.
      A meta-analysis of prehospital care times for trauma.
      Probability of fatal helicopter crash in 55-mile transport0.0000090.0000033–0.000046Blumen
      • Blumen I.
      A Safety Review and Risk Assessment in Air Medical Transport.
      Probability of a fatal ambulance crash in 55-mile transport0.000000340–0.0000015NHTSA
      >National Highway Traffic Safety Administration (NHTSA)
      NCSA data resource Website, Fatality Analysis Reporting System (FARS) Encyclopedia.
      Helicopter cost per transport, by distance in miles from trauma center, $Medicare
      Centers for Medicare & Medicaid Services ambulance fee schedule
      255,8005,400–6,800
      55 (base case)6,8006,400–7,800
      857,8007,400–8,800
      ALS ground ambulance cost per transport by distance in miles from trauma center, adjusted for longer road distance, $Medicare,
      Centers for Medicare & Medicaid Services ambulance fee schedule
      Diaz
      • Diaz M.A.
      • Hendey G.W.
      • Winters R.C.
      How far is that by air? the derivation of an air:ground coefficient.
      25900800–1,000
      55 (base case)1,1001,000–1,300
      851,4001,300–1,600
      Cost to replace helicopter if crashes, $4,200,0003,000,000–5,000,000Retail Web site
      Medical helicopter prices. FindTheBest.com [retail website].
      Cost to replace ambulance if crashes, $108,00080,000–140,000Retail Web site
      Ground ambulance prices, Arrow Manufacturing, Inc.
      QALYs lost in helicopter crash120Assumption
      QALYs lost in ground ambulance crash30Assumption
      Clinical assumptions
      Serious injury subgroup
      Mean baseline probability of inhospital death0.0760.056–0.096MacKenzie
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      RR ratio for inhospital mortality from helicopter EMS relative to ground EMS transport (1.00=no difference)N/A1.00–0.60Ringburg,
      • Ringburg A.N.
      • Thomas A.H.
      • Steyerberg E.W.
      • et al.
      Lives saved by helicopter emergency medical services: an overview of literature.
      Thomas,
      • Thomas S.H.
      • Cheema F.
      • Wedel S.K.
      • et al.
      Trauma helicopter emergency medical services transport: annotaed review of selected outcomes-related literature.
      • Thomas S.H.
      Helicopter emergency medical services transport outcomes literature: annotated review of articles published 2000-2003.
      • Thomas S.H.
      Helicopter EMS transport outcomes literature: annotated review of articles published 2004-2006.
      Brown,
      • Brown J.B.
      • Stassen N.A.
      • Bankey P.E.
      • et al.
      Helicopters and the civilian trauma system: national utilization patterns demonstrate improved outcomes after traumatic injury.
      • Brown B.S.
      • Pogu K.A.
      • Williams E.
      • et al.
      Helicopter EMS transport outcomes literature: annotated review of articles published 2007-2011.
      Taylor,
      • Taylor C.B.
      • Stevenson M.
      • Jan S.
      • et al.
      A systematic review of the costs and benefits of helicopter emergency medical services.
      Davis,
      • Davis D.P.
      • Peay J.
      • Serrano J.A.
      • et al.
      The impact of aeromedical response to patients with moderate to severe traumatic brain injury.
      Stewart,
      • Stewart K.E.
      • Cowan L.D.
      • Thompson D.M.
      • et al.
      Association of direct helicopter versus ground transport and in–hospital mortality in trauma patients: a propensity score analysis.
      Bulger,
      • Bulger E.M.
      • Guffey D.
      • Guyette F.X.
      • et al.
      Impact of prehospital mode of transport after severe injury: a multicenter evaluation from the Resuscitation Outcomes Consortium.
      Galvagno Jr.
      • Galvagno Jr, S.
      • Haut E.
      • Zafar S.
      • et al.
      Association between helicopter vs ground emergency medical services and survival for adults with major trauma.
      Mean probability of dying in 1 y, conditional on being discharged alive0.0300.010–0.050MacKenzie
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      1-y mean utility state (quality of life) after major trauma0.70N/AMacKenzie
      • MacKenzie E.J.
      • Weir S.
      • Rivara F.P.
      • et al.
      The value of trauma center care.
      1-y mean utility difference between helicopter vs ground ambulance survivors0−0.01, 0.01Ringburg,
      • Ringburg A.
      • Polinder S.
      • Meulman T.
      • et al.
      Cost–effectiveness and quality–of–life analysis of physician–staffed helicopter emergency medical services.
      Brazier
      • Brazier J.
      • Nicholl J.
      • Snooks H.
      The cost and effectiveness of the London helicopter emergency medical service.
      Yearly mortality rates beyond 1 y postinjuryUS life tablesN/ACDC
      Centers for Disease Control and Prevention (CDC)
      United States life tables, 2005.
      Mean mortality hazard ratio for decreased lifetime survival5.194.2–6.2Cameron
      • Cameron C.M.
      • Purdie S.M.
      • Kliewer E.V.
      • et al.
      Long-term mortality following trauma: 10 year follow-up in a population-based sample of injured adults.
      • Brown B.S.
      • Pogu K.A.
      • Williams E.
      • et al.
      Helicopter EMS transport outcomes literature: annotated review of articles published 2007-2011.
      Yearly decrease in quality of life during lifetimeN/AN/AHanmer
      • Hanmer J.
      • Lawrence W.F.
      • Anderson J.P.
      • et al.
      Report of nationally representative values for the noninstitutionalized US adult population for 7 health-related quality-of-life scores.
      Minor injury subgroup
      Mean baseline probability of inhospital death0.0130.010–0.015NTDB analysis
      RR ratio for inhospital mortality from helicopter EMS relative to ground EMS transport (1.00=no difference)1.00N/ARingburg,
      • Ringburg A.N.
      • Thomas A.H.
      • Steyerberg E.W.
      • et al.
      Lives saved by helicopter emergency medical services: an overview of literature.
      Thomas,
      • Thomas S.H.
      • Cheema F.
      • Wedel S.K.
      • et al.
      Trauma helicopter emergency medical services transport: annotaed review of selected outcomes-related literature.
      • Thomas S.H.
      Helicopter emergency medical services transport outcomes literature: annotated review of articles published 2000-2003.
      Taylor,
      • Thomas S.H.
      Helicopter EMS transport outcomes literature: annotated review of articles published 2004-2006.
      Galvagno Jr.
      • Galvagno Jr, S.
      • Haut E.
      • Zafar S.
      • et al.
      Association between helicopter vs ground emergency medical services and survival for adults with major trauma.
      Mean probability of dying in 1 y, conditional on being discharged alive0.0130.010–0.015Assumption based on MacKenzie
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      1-y mean utility state (quality of life) after minor trauma0.80N/APolinder
      • Polinder S.
      • Haagsma J.
      • Belt E.
      • et al.
      A systematic review of studies measuring health-related quality of life of general injury populations.
      1-y mean utility difference between helicopter vs ground ambulance survivors0−0.01, 0.01Ringburg,
      • Ringburg A.
      • Polinder S.
      • Meulman T.
      • et al.
      Cost–effectiveness and quality–of–life analysis of physician–staffed helicopter emergency medical services.
      Brazier
      • Brazier J.
      • Nicholl J.
      • Snooks H.
      The cost and effectiveness of the London helicopter emergency medical service.
      Yearly mortality rates beyond 1 y postinjuryUS life tablesN/ACDC
      Centers for Disease Control and Prevention (CDC)
      United States life tables, 2005.
      Mean mortality hazard ratio for decreased lifetime survival1.381.22–1.55Cameron
      • Cameron C.M.
      • Purdie S.M.
      • Kliewer E.V.
      • et al.
      Long-term mortality following trauma: 10 year follow-up in a population-based sample of injured adults.
      Yearly decrease in quality of life during lifetimeN/AN/AHanmer
      • Hanmer J.
      • Lawrence W.F.
      • Anderson J.P.
      • et al.
      Report of nationally representative values for the noninstitutionalized US adult population for 7 health-related quality-of-life scores.
      Cost assumptions
      Serious injury subgroup
      Cohort mean cost of hospitalization if discharged alive, $59,20054,500–63,900NSCOT analysis, MacKenzie,
      • MacKenzie E.J.
      • Weir S.
      • Rivara F.P.
      • et al.
      The value of trauma center care.
      Weir
      • Weir S.
      • Salkever D.S.
      • Rivara F.P.
      • et al.
      One-year treatment costs of trauma care in the USA.
      Cohort mean cost of hospitalization if death in hospital, $50,70045,400–56,000NSCOT analysis, MacKenzie,
      • MacKenzie E.J.
      • Weir S.
      • Rivara F.P.
      • et al.
      The value of trauma center care.
      Weir
      • Weir S.
      • Salkever D.S.
      • Rivara F.P.
      • et al.
      One-year treatment costs of trauma care in the USA.
      Cohort mean 1-y treatment costs after discharge from index hospitalization, $35,40033,000–38,000NSCOT analysis, MacKenzie,
      • MacKenzie E.J.
      • Weir S.
      • Rivara F.P.
      • et al.
      The value of trauma center care.
      Weir
      • Weir S.
      • Salkever D.S.
      • Rivara F.P.
      • et al.
      One-year treatment costs of trauma care in the USA.
      Yearly health care costs beyond 1 y postinjuryN/AN/ACMS
      Centers for Medicare & Medicaid Services (CMS) Office of the Actuary
      Health expenditures by age. Cited September 10, 2010.
      Hazard ratio for increased lifetime health care expenditures after major trauma1.451.39–1.51Cameron
      • Cameron C.M.
      • Purdie D.M.
      • Kliewer E.V.
      • et al.
      Ten-year health service use outcomes in a population-based cohort of 21,000 injured adults: the Manitoba Injury Outcome Study.
      Minor injury subgroup
      Cohort mean cost of hospitalization, $; includes ED care for ED discharges12,90011,900–13,800NSCOT analysis, Weir
      • Weir S.
      • Salkever D.S.
      • Rivara F.P.
      • et al.
      One-year treatment costs of trauma care in the USA.
      Cohort mean 1-y treatment costs after discharge from index hospitalization, $9,3008,300–10,200Davis
      • Davis K.L.
      • Joshi A.V.
      • Tortella B.J.
      • et al.
      The direct economic burden of blunt and penetrating trauma in a manage care population.
      Yearly health care costs beyond 1 y postinjuryN/AN/ACMS
      Centers for Medicare & Medicaid Services (CMS) Office of the Actuary
      Health expenditures by age. Cited September 10, 2010.
      Hazard ratio for increased lifetime health care expenditures after major trauma1.251.23–1.27Cameron
      • Cameron C.M.
      • Purdie D.M.
      • Kliewer E.V.
      • et al.
      Ten-year health service use outcomes in a population-based cohort of 21,000 injured adults: the Manitoba Injury Outcome Study.
      Annual discount rate for health expenditures and QALYs gained0.03N/AWeinstein
      • Weinstein M.C.
      • Siegel J.E.
      • Gold M.R.
      • et al.
      Recommendations of the Panel on Cost-effectiveness in Health and Medicine.
      AIS, Abbreviated Injury Score; NTDB, National Trauma Data Bank; NHTSA, National Highway Traffic Safety Administration; ALS, advanced life support; QALY, quality-adjusted life-year; RR, relative risk; CDC, Centers for Disease Control and Prevention; NSCOT, National Study on the Costs and Outcomes of Trauma; CMS, Centers for Medicare & Medicaid Services; ED, Emergency Department.
      For our base case, we assumed that patients are injured on average 55 miles (straight-line distance) away from the trauma center, according to the estimated mean distance traveled by helicopter scene patients transported to US trauma centers in the National Trauma Data Bank.
      • Brown J.B.
      • Stassen N.A.
      • Bankey P.E.
      • et al.
      Helicopters and the civilian trauma system: national utilization patterns demonstrate improved outcomes after traumatic injury.
      Given the wide regional variation in the costs and structure of EMS, costs per transport were standardized from the 2010 Medicare Fee Schedule and were adjusted to take into account the difference between longer road distances compared with the straight-line distances traveled by helicopters (Appendix E1, available online at http://www.annemergmed.com).
      • Diaz M.A.
      • Hendey G.W.
      • Winters R.C.
      How far is that by air? the derivation of an air:ground coefficient.
      Helicopter and ground ambulance safety were modeled as a risk of fatal crash per vehicle-mile traveled.
      • Blumen I.
      A Safety Review and Risk Assessment in Air Medical Transport.
      Unfortunately, there are no reliable nationally representative data on ground ambulance safety because crashes and distances traveled in operation are not uniformly reported.
      • Blumen I.
      A Safety Review and Risk Assessment in Air Medical Transport.
      To conservatively address the concerns with relative safety of helicopter transport, we used the best-case scenario for ground ambulance safety (ie, the risk of a fatal crash for a commercial light truck) in the reference case analysis.
      >National Highway Traffic Safety Administration (NHTSA)
      NCSA data resource Website, Fatality Analysis Reporting System (FARS) Encyclopedia.
      Our analysis included crewmember fatalities caused by a fatal crash, as well as the cost of replacing the vehicle. We conducted sensitivity analyses around these assumptions.
      The effectiveness of helicopter transport compared with ambulance transport was modeled as the differential probability of inhospital death for patients with serious injuries (Abbreviated Injury Score 3 to 6). We assessed differences in costs and outcomes by EMS transport mode over a range of the RR reduction, from 1.00 to 0.60 (or 40% risk reduction), because greater reductions would be very unlikely (further details in Appendix E1, available online at http://www.annemergmed.com).
      Costs for patients with serious and minor injury treated at US trauma centers were derived with NSCOT cost data. For seriously injured patients, we considered the cost of hospitalization, as well as posthospitalization care (rehospitalization, long-term care, rehabilitation, outpatient care, and informal care). It also takes into account the differential in costs for patients who die in the hospital compared with those who are discharged alive. To derive costs for patients with minor injury who were taken to US trauma centers, we analyzed cost data from 993 patients excluded from the published NSCOT studies
      • MacKenzie E.J.
      • Rivara F.P.
      • Jurkovich G.J.J.
      • et al.
      A national evaluation of the effect of trauma-center care on mortality.
      because of having minor injuries (maximum Abbreviated Injury Score 1 to 2) to determine the mean cost of trauma center care for this group. We used previously described methods for analyzing the cost data from NSCOT.
      • Weir S.
      • Salkever D.S.
      • Rivara F.P.
      • et al.
      One-year treatment costs of trauma care in the USA.
      A Markov model was used to project incremental differences in lifetime survival and health care expenditures beyond 1-year postinjury (Figure 1). We assumed that mode of EMS transport does not affect survival beyond the initial hospitalization because there have been no studies evaluating transport mode survival beyond hospitalization. US life tables were used to calculate remaining life expectancy.
      Centers for Disease Control and Prevention (CDC)
      United States life tables, 2005.
      Mortality rates derived from the life tables were adjusted to reflect decreased survival after major trauma according to a 10-year longitudinal study of trauma victims.
      • Cameron C.M.
      • Purdie S.M.
      • Kliewer E.V.
      • et al.
      Long-term mortality following trauma: 10 year follow-up in a population-based sample of injured adults.
      Quality-adjusted life-years were calculated with the mean observed values of the Short Form-6 Dimension (SF-6D) scale in the NSCOT cohort at 1 year postinjury (0.70).
      • MacKenzie E.J.
      • Weir S.
      • Rivara F.P.
      • et al.
      The value of trauma center care.
      As assumed in previous research, utilities were decreased during a lifetime proportional to differences in SF-6D scores by age reported for the general US population.
      • MacKenzie E.J.
      • Weir S.
      • Rivara F.P.
      • et al.
      The value of trauma center care.
      • Hanmer J.
      • Lawrence W.F.
      • Anderson J.P.
      • et al.
      Report of nationally representative values for the noninstitutionalized US adult population for 7 health-related quality-of-life scores.
      In our base case assumption, we assumed that there was no difference in quality of life according to transport mode for patients who survive past 1 year,
      • Brazier J.
      • Nicholl J.
      • Snooks H.
      The cost and effectiveness of the London helicopter emergency medical service.
      • Ringburg A.
      • Polinder S.
      • Meulman T.
      • et al.
      Cost–effectiveness and quality–of–life analysis of physician–staffed helicopter emergency medical services.
      but we varied this assumption in sensitivity analysis. The Markov model was also used to project lifetime health care costs beyond 1 year according to Centers for Medicare & Medicaid Services age-specific estimates of annual health care expenditures.
      • Hartman M.
      • Catlin A.
      • Lassman D.
      • et al.
      US health spending by age, selected years through 2004.
      Centers for Medicare & Medicaid Services (CMS) Office of the Actuary
      Health expenditures by age. Cited September 10, 2010.
      These costs were adjusted to account for the increased health expenditures of major trauma victims compared with the general US population.
      • Cameron C.M.
      • Purdie D.M.
      • Kliewer E.V.
      • et al.
      Ten-year health service use outcomes in a population-based cohort of 21,000 injured adults: the Manitoba Injury Outcome Study.
      We applied an annual 3% discount rate to both quality-adjusted life-years and costs (Appendix E1, available online at http://www.annemergmed.com).
      • Weinstein M.C.
      • Siegel J.E.
      • Gold M.R.
      • et al.
      Recommendations of the Panel on Cost-effectiveness in Health and Medicine.

       Analysis

      Helicopter and ground ambulance trauma transport were compared in terms of quality-adjusted life-years, total lifetime costs expressed in 2009 dollars using the Gross Domestic Product deflator,
      • Kumaranayake L.
      The real and the nominal? making inflationary adjustments to cost and other economic data.
      and incremental cost-effectiveness ratios, which were defined as the ratio of the total lifetime costs associated with transport by helicopter EMS minus the total lifetime costs associated with ground EMS divided by the difference between the lifetime quality-adjusted life-years after helicopter EMS and the quality-adjusted life-years after ground EMS. Robustness was assessed with 1-way sensitivity analyses and probabilistic sensitivity analysis of all model inputs.
      For our probabilistic sensitivity analyses, we performed 100,000 second-order Monte Carlo simulation trials that selected values of all input parameters from the ranges described in Table 1 according to distributions that represent the uncertainty in their estimation (Table E6, available online at http://www.annemergmed.com). This allows for assessing the effect of the joint uncertainty across all parameters in the model on its estimated outcomes (Appendix E1, available online at http://www.annemergmed.com).
      • Briggs A.
      • Sculpher M.
      • Claxton K.
      Decision Modelling for Health Economic Evaluation.
      We then determined the RR reduction in mortality for helicopter EMS to cost less than $100,000 per quality-adjusted life-year gained in at least 95% of simulations (ie, to have a least a 95% probability of being cost-effective at this threshold). All analyses were conducted with TreeAge Pro Suite 2009 (TreeAge Software, Inc., Williamstown, MA), with input probability distributions verified with Stata (version 12.0; StataCorp, College Station, TX).

      Results

      Using the base case assumptions, helicopter EMS needs to provide a 15% reduction in mortality (RR 0.85) for patients with serious injuries (Abbreviated Injury Score 3 to 6) to be below the threshold of $100,000 per quality-adjusted life-year gained (Figure 2A). Given the baseline inhospital mortality of 7.6% for the base case, a 15% RR reduction equates to a 1.3% reduction in absolute mortality. Thus, helicopter EMS would have to save a minimum of 1.3 lives per 100 patient transports with mean characteristics of the NSCOT cohort to be cost-effective. Helicopter EMS would need to reduce mortality by an even larger amount, 30% (RR 0.70), or save more than 3.3 lives per 100 transports to cost less than $50,000 per quality-adjusted life-year gained.
      Figure thumbnail gr2
      Figure 2Relationship between relative reduction in mortality and the cost-effectiveness of helicopter EMS. A, Base case analysis. The plotted line represents the cost-effectiveness of helicopter EMS relative to ground EMS as a function of the assumed mortality reduction provided by helicopter EMS, given the base case assumptions described in . B, Effect of overtriage rate on cost-effectiveness of helicopter EMS. According to analysis of national data, 36% of patients transported by helicopter EMS have only minor injuries. The 2 dotted lines demonstrate how the cost-effectiveness of helicopter EMS changes according to the highest and lowest regional overtriage rates observed in national data. C, Effect of difference in disability outcomes on cost-effectiveness of helicopter EMS. In our base case, we assume no difference in disability outcomes. The 2 dotted lines demonstrate how the cost-effectiveness of helicopter EMS changes according to whether helicopter EMS is associated with worse or better disability outcomes as measured by the SF-6D quality of life scale during the course of a lifetime. ICER, incremental cost-effectiveness ratio.
      These findings assume that the overtriage rate (patients with minor injuries who were triaged to helicopter EMS) was equal to the national average for US Level I or II trauma centers (36%). Across US regions, there is variability in the overtriage rate from 9% to 69%. Our results are sensitive to this variability (Figure 2B). In the region with the lowest overtriage rate (9%), only a 11% reduction in mortality (RR 0.89) would be needed for helicopter EMS to cost less than $100,000 per quality-adjusted life-year. Conversely, in the region with the highest overtriage rate (69%), the threshold is much higher, with a needed mortality reduction of 26% (RR 0.74).
      The cost-effectiveness of helicopter transport depends heavily on assumptions about whether there are differences in long-term patient disability outcomes by transport mode (Figure 2C). If helicopter EMS enabled a sustained improvement in quality of life by 0.01 on the SF-6D utility scale during the course of a lifetime, helicopter transport would be cost-effective at $77,771 per quality-adjusted life-year. However, if helicopter transport survivors were found to have a lower quality of life by 0.01 compared with ground ambulance survivors, helicopter EMS would need to provide at least a 27% reduction in mortality (RR 0.73) to cost less than $100,000 per quality-adjusted life-year.
      The cost-effectiveness of helicopter transport decreases as the marginal cost of helicopter transport over ground transport increases from the base-case assumption of $5,700 (Figure 3). However, even if helicopter transport costs $10,000 more per transport than ground transport, as it might in rural areas with low flight volume, it would cost less than $100,000 per quality-adjusted life-year if mortality reductions of more than 25% could be achieved.
      Figure thumbnail gr3
      Figure 3Effect of the variation in the added cost of helicopter EMS on the threshold mortality reduction needed to be cost-effective. According to the Medicare Fee Schedule, we assume that the helicopter EMS costs about $5,700 more than ground EMS transport for patients located 55 miles from a trauma center (our base case assumption). The plotted lines demonstrate how the cost-effectiveness of helicopter EMS would change according to the assumed relative mortality reduction and the regional variation in the added cost of helicopter EMS over ground EMS.
      Our findings did not change across the range of uncertainty in how much more likely it would be for helicopter EMS to have a fatal crash during transport (Figure E3, available online at http://www.annemergmed.com). Table 2 summarizes the relative mortality reduction for patients with serious injuries (Abbreviated Injury Score 3 to 6) needed for helicopter EMS to be cost-effective according to various scenarios and cost-effectiveness thresholds. The table also shows the number of lives helicopter EMS needs to save per 100 transports of patients with serious injury, the population whose outcomes may potentially be sensitive to helicopter versus ground EMS. This number ranged from the lowest value of 0 in the case of helicopters being associated with lower long-term disability to 3.3 in the case in which the incremental costs of a helicopter versus ground transport was $15,000.
      Table 2Summary results of scenario analyses: minimum reduction in mortality among patients with serious injury triaged to helicopter EMS to be cost-effective relative to ground EMS.
      Assumes that there is a range of patients with minor injuries (AIS 1 to 2) also triaged to helicopter transport (base case analysis=36% unless otherwise indicated) and that patients with minor injuries have no difference in outcomes conditional on transport mode.
      Scenario$100,000 per QALY-Gained Threshold$50,000 per QALY-Gained Threshold
      RR Ratio for Inhospital MortalityLives Needed to Be Saved per 100 Transports (AIS 3–6)RR Ratio for Inhospital MortalityLives Needed to Be Saved per 100 Transports (AIS 3–6)
      Base case analysis0.851.30.703.3
      Overtriage of patients with minor injury (maximum AIS 1–2)
       Base case analysis (36%)
       Perfect (0%)0.900.80.792.0
       Lowest observed region (8%)0.890.90.782.1
       Highest observed region (69%)0.742.70.566.5
      Difference in disability outcomes
       Base case analysis (no difference)
       Helicopter better (0.01 higher SF-6D)1.0000.811.8
       Helicopter worse (0.01 lower SF-6D)0.732.80.545.1
      Added per-transport cost of helicopter EMS over ground EMS, $
       Base case analysis (5,700)
       3,0000.920.70.821.7
       7,5000.821.70.654.1
       10,0000.782.10.595.3
       12,5000.742.70.536.7
       15,0000.703.30.497.9
      Distance from trauma center, miles
       Base case analysis (55)
       250.871.10.732.8
       850.841.40.683.6
      —, same results from base case analysis.
      low asterisk Assumes that there is a range of patients with minor injuries (AIS 1 to 2) also triaged to helicopter transport (base case analysis=36% unless otherwise indicated) and that patients with minor injuries have no difference in outcomes conditional on transport mode.
      For helicopter EMS to have a 95% probability of being cost-effective at a $100,000 per quality-adjusted life-year threshold, given the joint uncertainty of all model parameters, a mortality reduction of 26% (RR 0.74; 2.7 lives saved per 100 patients with serious injury) would be needed (Figure 4).
      Figure thumbnail gr4
      Figure 4Probabilistic sensitivity analysis of the incremental cost-effectiveness ratio of helicopter EMS versus ground EMS for trauma scene transport according to the size of the relative mortality reduction from helicopter EMS. A threshold mortality reduction of greater than 26% (RR 0.74) is needed for helicopter EMS to be cost-effective in greater than 95% of simulations if society is willing to pay $100,000 per QALY gained. This is a higher threshold mortality reduction than the threshold of 15% (RR 0.85) that was determined with base-case assumptions. The threshold of 15% (RR 0.85) was cost-effective in 51% of simulations if society is willing to pay $100,000 per QALY gained.

      Limitations

      Given that there have been no previous studies comparing the long-term costs and outcomes by EMS transport mode, this analysis has a number of limitations. The decision model required certain assumptions and used data from national data sets and numerous published studies. The results and conclusions are therefore specific to those assumptions and data. For example, baseline mortality probabilities and hospitalization costs inputs were derived from NSCOT, in which most trauma centers were located in urban and suburban areas. Although we conducted sensitivity analyses around these assumptions, baseline mortality probabilities and costs may be different for injured patients taken rural trauma centers not represented in NSCOT.
      Second, we focus on the average patient requiring trauma center care from NSCOT because the outcomes and costs of such patients are already published. Results further stratified by age and injury severity are not yet available, though they can be incorporated into the model as soon as they are published. We speculate that the relative mortality reduction needed for helicopter transport to be cost-effective would need to be higher for older patients and that the reduction needed for the transport of more severely injured patients could be lower, though the relative magnitude of these effects remains to be assessed.
      Third, the analyses also assume that ground ambulances can leave their local area for long-distance transport without undue consequences in terms of decreased coverage for responding to other emergencies. In practice, many ground ambulances crews in rural areas in which EMS coverage is sparse are reluctant to perform long-distance transports.
      • Thomson D.P.
      • Thomas S.H.
      Guidelines for air medical dispatch.
      Thus, our results are most relevant to situations in which long-distance ground ambulance transport can be performed without causing decrements in EMS response to other emergencies in that area. Likewise, the base case costs per transport assume equal existing availability of ground and helicopter EMS for transport. Although our sensitivity analysis assesses how our results would change according to a wide range in the marginal difference between helicopter and ground EMS transport costs, we do not explicitly model the regional variation in EMS system costs. Indeed, in areas in which ground EMS coverage is nonexistent, fully replacing helicopter EMS coverage would require up to 6 new ground EMS vehicles, resulting in substantially higher costs per ground transport for the same number of patients transported.
      • Bruhn J.D.
      • Williams K.A.
      • Aghababian R.
      True costs of air medical vs ground ambulance systems.
      Fourth, we did not compare helicopter EMS transport to a trauma center versus ground EMS transport to a local nontrauma center because virtually all the studies on helicopter versus ground EMS have compared only outcomes of direct transport to a trauma center. Because direct transport to a trauma center rather than a nontrauma center has been shown to reduce mortality, a significant unstudied benefit of helicopter EMS may be in extending direct access to trauma center care when direct transport by ground EMS is not logistically feasible.

      Discussion

      Compared with ground EMS transport, helicopter scene transport is cost-effective if it results in a reduction in the RR of death for seriously injured trauma patients of at least 15%, given our model assumptions. This translates into the need to save at least 1.3 lives per 100 patients transported with serious injury. Given current uncertainties, helicopter EMS must reduce mortality by more than 26% (2.7 lives per 100 transports with serious injury) to have a 95% probability of being cost-effective at less than $100,000 per quality-adjusted life-year gained. To meet the more conservative threshold of costing less than $50,000 per quality-adjusted life-year gained, helicopter EMS needs to reduce mortality by 30%.
      There is one other study on the cost-effectiveness of helicopter EMS for trauma in the United States.
      • Gearhart P.A.
      • Wuerz R.
      • Localio A.R.
      Cost-effectiveness analysis of helicopter EMS for trauma patients.
      However, this study did not calculate incremental cost-effectiveness ratios from a societal perspective during a lifetime horizon, as recommended by the Panel of Cost-effectiveness in Health and Medicine, which limits its validity.
      • Weinstein M.C.
      • Siegel J.E.
      • Gold M.R.
      • et al.
      Recommendations of the Panel on Cost-effectiveness in Health and Medicine.
      It is not clear whether the current practice of helicopter scene transport meets the minimum threshold mortality reduction for helicopter transport defined in this study. Although some studies of helicopter transport meet this threshold, all are observational and most have major methodological limitations. Almost all previous helicopter transport studies are limited by the fact that the majority of patients in the ground EMS control group may not have been eligible for helicopter EMS because they may have been injured too close to the hospital.
      • Baxt W.
      • Moody P.
      The impact of a rotorcraft aeromedical transport emergency care service on trauma mortality.
      • Moylan J.A.
      • Fitzpatrick K.T.
      • Beyer A.
      Factors improving survival in multisystem trauma patients.
      • Schwartz R.
      • Jacobs L.
      • Juda R.
      A comparison of ground paramedics and aeromedical treatment of severe blunt trauma patients.
      • Nardi G.
      • Massarutti D.
      • Muzzi R.
      Impact of emergency medical helicopter service on mortality for trauma in north-east Italy: a regional prospective audit.
      • Moront M.
      • Gotschall C.
      • Eichelberger M.
      Helicopter transport of injured children: system effectiveness and triage criteria.
      • Cunningham P.
      • Rutledge R.
      • Baker C.C.
      • et al.
      A comparison of the association of helicopter and ground ambulance transport with the outcome of injury in trauma patients transported from the scene.
      • Jacobs L.
      • Gabram S.
      • Sztajnkrycer M.
      • et al.
      Helicopter air medical transport: ten-year outcomes for trauma patients in a New England program.
      • Buntman A.
      • Yeomans K.
      The effect of air medical transport on survival after trauma in Johannesburg, South Africa.
      • Thomas S.H.
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      • et al.
      Helicopter transport and blunt trauma mortality: a multicenter trial.
      • Poste J.C.
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      • Ochs M.
      • et al.
      Air medical transport of severely head-injured patients undergoing paramedic rapid sequence intubation.
      • Davis D.P.
      • Peay J.
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      • et al.
      The impact of aeromedical response to patients with moderate to severe traumatic brain injury.
      • DiBartolomeo S.
      • Sanson G.
      • Nardi G.
      • et al.
      HEMS vs Ground-BLS care in traumatic cardiac arrest.
      • Brown J.B.
      • Stassen N.A.
      • Bankey P.E.
      • et al.
      Helicopters and the civilian trauma system: national utilization patterns demonstrate improved outcomes after traumatic injury.
      • Mitchell A.D.
      • Tallon J.M.
      • Sealy B.
      Air versus ground transport of major trauma patients to a tertiary trauma centre: a province-wide comparison using TRISS analysis.
      • Sullivent E.E.
      • Faul M.
      • Wald M.M.
      Reduced mortality in injured adults transported by helicopter emergency medical services.
      • Stewart K.E.
      • Cowan L.D.
      • Thompson D.M.
      • et al.
      Association of direct helicopter versus ground transport and in–hospital mortality in trauma patients: a propensity score analysis.
      • Galvagno Jr, S.
      • Haut E.
      • Zafar S.
      • et al.
      Association between helicopter vs ground emergency medical services and survival for adults with major trauma.
      Not excluding ground EMS patients injured close to the trauma center, who are less likely to die in the field than those who are injured far away and survive to be transported,
      • Rogers F.B.
      • Shackford S.R.
      • Hoyt D.B.
      • et al.
      Trauma deaths in a mature urban vs rural trauma system: a comparison.
      likely biases outcomes in favor of helicopter EMS.
      • Delgado M.K.
      • Newgard C.D.
      • Hsia R.Y.
      Helicopter vs ground transportation for patients with trauma.
      • Galvagno S.M.
      • Baker S.P.
      • Haider A.H.
      Helicopter vs ground transportation for patients with trauma—reply.
      A systematic review of studies attempted to risk-adjust for the population heterogeneity observed in these studies and estimated that on average helicopter EMS saves 2.7 lives per 100 transports.
      • Ringburg A.N.
      • Thomas A.H.
      • Steyerberg E.W.
      • et al.
      Lives saved by helicopter emergency medical services: an overview of literature.
      However, the risk adjustment tool used (TRISS: Trauma Score–Injury Severity Score) has extensive limitations,
      • Moore L.
      • Lavoie A.
      • Turgeon A.F.
      • et al.
      The trauma risk adjustment model: a new model for evaluating trauma care.
      and this study excluded several relevant studies that used logistic regression models.
      The largest and most rigorous multicenter study to date is a retrospective analysis of 223,475 transports in the National Trauma Data Bank, which estimated that helicopter EMS was associated with a 16% increase in the odds of survival (odds ratio 1.16; 95% confidence interval [CI] 1.14 to 1.17), or 1.5 lives saved per 100 patients with severe injury (95% CI 1.4 to 1.6) taken to Level I trauma centers.
      • Galvagno Jr, S.
      • Haut E.
      • Zafar S.
      • et al.
      Association between helicopter vs ground emergency medical services and survival for adults with major trauma.
      Even after risk adjustment, the study also found that survivors of helicopter EMS were less likely to be discharged home without services (48% versus 57%; P<.001) than survivors of ground EMS.
      • Galvagno Jr, S.
      • Haut E.
      • Zafar S.
      • et al.
      Association between helicopter vs ground emergency medical services and survival for adults with major trauma.
      These results indicate that helicopter survivors likely had worse disability outcomes than ground EMS survivors.
      If survivors of helicopter EMS have relatively worse disability outcomes, such as being less likely to survive neurologically intact, we found that a much higher mortality reduction is needed (27%; Figure 2C) for helicopter EMS to be considered cost-effective. The authors also performed a sensitivity analysis excluding ground transports likely not eligible for helicopter transport, according to available data on transport time, and found the estimated survival benefit was cut in half, from 16% to 7% (odds ratio 1.07; 95% CI 1.04 to 1.17).
      • Delgado M.K.
      • Newgard C.D.
      • Hsia R.Y.
      Helicopter vs ground transportation for patients with trauma.
      • Galvagno S.M.
      • Baker S.P.
      • Haider A.H.
      Helicopter vs ground transportation for patients with trauma—reply.
      This further suggests that use of helicopter EMS for transport to most trauma centers in this study was not cost-effective.
      A recent Oklahoma trauma registry study found that helicopter EMS was associated with a reduction in 2-week mortality of 33% (hazard ratio 0.67; 95% CI 0.54 to 0.84) for patients with serious injury.
      • Stewart K.E.
      • Cowan L.D.
      • Thompson D.M.
      • et al.
      Association of direct helicopter versus ground transport and in–hospital mortality in trauma patients: a propensity score analysis.
      Another study of 10,314 patients with moderate to severe head injury (Abbreviated Injury Score >3) with a baseline mortality rate of 23% transported to 5 San Diego trauma centers found that helicopter EMS was associated with an adjusted odds ratio of 1.90 for hospital survival (95% CI 1.60 to 2.20) and an adjusted odds ratio for discharge home without services of 1.36 (95% CI 1.18 to 1.58). Although these estimates appear to meet or exceed the risk reductions needed for helicopter EMS cost-effectiveness, both studies are limited by selection bias because they did not exclude the majority of ground EMS transports that were likely ineligible for helicopter EMS because patients were injured too close to the hospital.
      Finally, a recent secondary analysis of Resuscitation Outcomes Consortium data collected to evaluate outcomes of severe injury did not find a significant association between helicopter EMS and 28-day survival (odds ratio 1.11; 95% CI 0.82 to 1.51).
      • Bulger E.M.
      • Guffey D.
      • Guyette F.X.
      • et al.
      Impact of prehospital mode of transport after severe injury: a multicenter evaluation from the Resuscitation Outcomes Consortium.
      Other studies have found either no benefit from helicopter EMS
      • Schiller W.
      • Knox R.
      • Zinnecker H.
      Effect of helicopter transport of trauma victims on survival in an urban trauma center.
      • Nicholl J.
      • Brazier J.
      • Ha S.
      Effects of London helicopter emergency medical services on survival after trauma.
      • Brathwaite C.
      • Rosko M.
      • McDowell R.
      A critical analysis of on-scene helicopter transport on survival in a statewide trauma system.
      • Chappell V.
      • Mileski W.
      • Wolf S.
      • et al.
      Impact of discontinuing a hospital-based air ambulance service on trauma patient outcomes.
      • Biewener A.
      • Aschenbrenner U.
      • Rammelt S.
      • et al.
      Impact of helicopter transport and hospital level on mortality of polytrauma patients.
      • Talving P.
      • Teixeira P.G.
      • Barmparas G.
      • et al.
      Helicopter evacuation of trauma victims in Los Angeles: does it improve survival?.
      or are subject to the same methodological limitations outlined above.
      • Baxt W.
      • Moody P.
      The impact of a rotorcraft aeromedical transport emergency care service on trauma mortality.
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      Factors improving survival in multisystem trauma patients.
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      • Moront M.
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      • Cunningham P.
      • Rutledge R.
      • Baker C.C.
      • et al.
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      • Jacobs L.
      • Gabram S.
      • Sztajnkrycer M.
      • et al.
      Helicopter air medical transport: ten-year outcomes for trauma patients in a New England program.
      • Buntman A.
      • Yeomans K.
      The effect of air medical transport on survival after trauma in Johannesburg, South Africa.
      • Thomas S.H.
      • Harrison T.H.
      • Buras W.R.
      • et al.
      Helicopter transport and blunt trauma mortality: a multicenter trial.
      • Poste J.C.
      • Davis D.P.
      • Ochs M.
      • et al.
      Air medical transport of severely head-injured patients undergoing paramedic rapid sequence intubation.
      • Davis D.P.
      • Peay J.
      • Serrano J.A.
      • et al.
      The impact of aeromedical response to patients with moderate to severe traumatic brain injury.
      • DiBartolomeo S.
      • Sanson G.
      • Nardi G.
      • et al.
      HEMS vs Ground-BLS care in traumatic cardiac arrest.
      • Brown J.B.
      • Stassen N.A.
      • Bankey P.E.
      • et al.
      Helicopters and the civilian trauma system: national utilization patterns demonstrate improved outcomes after traumatic injury.
      • Mitchell A.D.
      • Tallon J.M.
      • Sealy B.
      Air versus ground transport of major trauma patients to a tertiary trauma centre: a province-wide comparison using TRISS analysis.
      • Sullivent E.E.
      • Faul M.
      • Wald M.M.
      Reduced mortality in injured adults transported by helicopter emergency medical services.
      In summary, there is limited evidence in the comparative effectiveness literature to conclude that helicopter EMS is cost-effective relative to ground EMS for most patients in the United States, given current rates of overtriage. Whether helicopter EMS is cost-effective for certain age and injury subgroups remains to be answered in future research. This study is the first to define the clinical benefit needed to make helicopter transport cost-effective relative to ground ambulance for trauma.
      Our study also highlights the effect that differences in disability outcomes can have on cost-effectiveness. We found that any measurable improvement in long-term disability outcomes would make helicopter transport cost-effective even if no lives were saved relative to ground transport.
      To our knowledge, this is also the first cost-effectiveness analysis that takes into account the high proportion of patients who are triaged to helicopter EMS who have only minor injuries. Although a proportion of these patients with minor injury require air medical transport because of logistic and topographic considerations, patients with minor injury who are unnecessarily transported by helicopter cannot be expected to have improved outcomes despite the greater expense.
      Our findings also imply that reducing overtriage of minor injury to helicopter EMS is the most promising avenue for increasing the cost-effectiveness of this critical care intervention. For example, the outcomes after activating helicopter EMS according to crash mechanism only, or after routine use of helicopter “auto-launch” at the 911 call instead of after local EMS assessment at the scene, should be further scrutinized because these practices likely lead to overtriage. Our model also implies that the value of helicopter EMS needs to be evaluated on a regional and geographic basis. For example, a rural region that has a high cost of helicopter transport because of low flight volume (eg, <400 transports per year, with a cost per transport of $10,000) could potentially offset this high cost of transport by ensuring that seriously injured patients are transported by helicopter to a trauma center. Because mortality for rural trauma is twice as high as in urban areas, this may represent a cost-effective opportunity for improvement.
      • Rogers F.B.
      • Shackford S.R.
      • Hoyt D.B.
      • et al.
      Trauma deaths in a mature urban vs rural trauma system: a comparison.
      • Peek-Asa C.
      • Zwerling C.
      • Stallones L.
      Acute traumatic injuries in rural populations.
      • Grossman D.C.
      • Kim A.
      • Macdonald S.C.
      • et al.
      Urban-rural differences in prehospital care of major trauma.
      We also found that current helicopter crash rates do not affect cost-effectiveness, except when there is very little clinical benefit from helicopter transport, because the probability of helicopter crash is still very low. This is the case even though we assume the best-case scenario for ground transport, that they have a minimum fatal crash risk comparable to commercial light trucks. In reality, ground ambulance crash risks are likely higher especially during lights-and-sirens operations.
      In existing US EMS systems in which both ground and helicopter transport from the scene of injury are feasible, helicopter EMS must reduce mortality by at least 15% to compare favorably to other health care interventions that are considered cost-effective. Helicopter EMS would also be considered cost-effective with smaller mortality reductions, as long an improvement in long-term disability outcomes is also demonstrated. It is not clear from the literature that helicopter EMS achieves this threshold mortality reduction, leaving its cost-effectiveness in doubt relative to ground EMS for the majority of US patients transported to trauma centers. Reducing the overtriage of patients with minor injury to helicopter EMS is a promising avenue for improving its cost-effectiveness. Further rigorous study of the health outcomes of helicopter EMS, including the effect of helicopter transport on long-term disability, is needed to better assess the value of this frequently used, critical care intervention in the United States.
      The authors acknowledge Ellen Mackenzie, PhD, Johns Hopkins University, for granting us permission to analyze the primary cost data collected for the National Study on the Cost and Outcomes of Trauma; and Alan Garber, MD, PhD, Harvard University, for his insightful comments and suggestions during the earlier phases of this research.

      Appendix

      Supplementary Materials

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      • Correction
        Annals of Emergency MedicineVol. 63Issue 4
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          In the October 2013 issue, in the article by Delgado et al (“Cost-Effectiveness of Helicopter Versus Ground Emergency Medical Services for Trauma Scene Transport in the United States,” pages 351-364) there was an error in the reference section. Reference 31 should have read:
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