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Trauma Versus Nontrauma Patients Treated by the Danish Helicopter Emergency Medical Service: A Register-Based Study of Patient Characteristics, Hospitalization, and Mortality

Open AccessPublished:June 21, 2021DOI:https://doi.org/10.1016/j.amj.2021.05.005

      Abstract

      Objective

      Helicopter emergency medical services (HEMS) are part of many emergency health care systems, ensuring specialized treatment on scene. An accurate use is important for improved resource utilization. The aim of this study was to describe patient characteristics, hospitalization, and mortality in trauma and nontrauma patients seen by the Danish HEMS teams.

      Methods

      The study is a registry-based study presenting data from the national Danish HEMS database. We included all HEMS missions from October 1, 2014, to April 30, 2018.

      Results

      A total of 13,391 HEMS entries were registered, and 5,524 cases were included in the study. Trauma patients were younger (38 vs. 63 years) and had a lower level of comorbidities (Charlson Comorbidity Index 0: 82% vs. 58%) compared with nontrauma patients. More nontrauma cases were classified with a severity score corresponding to a critical emergency. They also had a higher 30-day mortality compared with trauma patients (26% vs. 11%).

      Conclusion

      This national study demonstrated differences in demographics, the severity profile, and mortality among trauma compared with nontrauma patients that could possibly indicate an overuse of HEMS for minor trauma cases. The results might suggest that educational efforts and a review of the current dispatch guidelines could be of importance when trying to improve the use of HEMS.
      Helicopter emergency medical services (HEMS) are an integrated part of the emergency health care system in many countries. They are mainly dispatched to patients with suspected critical emergencies in which both specialized treatment on scene and rapid transfer to definitive care may be crucial for the patient's outcome.

      Secretary TNDHS. 2020. Available at: http://www.akutlaegehelikopter.dk. Accessed 10 February 2021.

      • Krebs MG
      • Fletcher EN
      • Werman H
      • McKenzie LB
      Characteristics of nontrauma scene flights for air medical transport.

      European HEMS and Air Ambulance Committee EHAC. April 16, 2020. Available at: http://ehac.eu/about.html. Accessed 10 February 2021.

      • Neagle G
      • Curatolo L
      • Ferris J
      • Donald M
      • Hearns S
      • Corfield AR
      Epidemiology and location of primary retrieval missions in a Scottish aeromedical service.
      The Danish national HEMS was introduced in 2014
      • Alstrup K
      • Petersen JA
      • Barfod C
      • Knudsen L
      • Rognås
      • Møller TP
      The Danish helicopter emergency medical service database: high quality data with great potential.
      • Knudsen L
      • Stengaard C
      • Hansen TM
      • Lassen JF
      • Terkelsen CJ
      Earlier reperfusion in patients with ST-elevation myocardial infarction by use of helicopter.
      • Hesselfeldt R
      • Steinmetz J
      • Jans H
      • et al.
      Impact of a physician-staffed helicopter on a regional trauma system: a prospective, controlled, observational study.
      • Funder KS
      • Rasmussen LS
      • Lohse N
      • Siersma V
      • Hesselfeldt R
      • Steinmetz J
      Long-term follow-up of trauma patients before and after implementation of a physician-staffed helicopter: a prospective observational study.
      to ensure the availability of physician-provided prehospital critical care and rapid access to specialized hospital treatment for all patients regardless of their location, thus compensating for the reorganization and centralization of specialized treatments that have been recently implemented in the Danish health care system.

      Styrket Akutberedskab - planlægningsgrundlag for det regionale sundhedvæsen. Available at: https://www.sst.dk/-/media/Udgivelser/2007/Publ2007/PLAN/Akutberedskab/StyrketAkutberedskab,-d-,pdf.ashx. Accessed.

      Since its implementation, the use of HEMS in Denmark has increased yearly.

      Secretary TNDHS. 2020. Available at: http://www.akutlaegehelikopter.dk. Accessed 10 February 2021.

      HEMS is a limited prehospital resource and may be more costly than ground emergency medical services (EMS), emphasizing the need for accurate use. Knowledge about the characteristics and outcomes of the Danish HEMS patient population is considered to be fundamental in order to improve dispatch, resource use, and patient safety.
      The Danish HEMS is dispatched to both trauma and nontrauma patients, which may increase the complexity of the dispatch criteria. In a recently published study, a possible overtriage of HEMS (eg, dispatch of HEMS for patients who do not need this advanced service) to seemingly minor traumatic events was suggested.
      • Alstrup K
      • Møller TP
      • Knudsen L
      • et al.
      Characteristics of patients treated by the Danish Helicopter Emergency Medical Service from 2014-2018: a nationwide population-based study.
      HEMS overtriage can result in decreased service availability and, therefore, impact its benefits. Thus, increasing our knowledge regarding HEMS dispatch for injured patients (trauma) versus patients with a medical condition (nontrauma) may have an impact on future HEMS dispatch protocols.
      The aim of this study was to describe patient characteristics in terms of demographics, severity score, critical care interventions performed, clinical course in the hospital, and mortality in trauma and nontrauma patients seen by the Danish HEMS teams.

      Methods

       Study Design

      The study is a registry-based study presenting and analyzing data from the national Danish HEMS database. All HEMS missions from October 1, 2014, to April 30, 2018, were included in the study. According to the Central Denmark Region Regional Committee on Health Research Ethics, no ethical approval was needed (j.nr.: 1-10-72-4-17).

       Setting

      Denmark is a relatively flat country of around 43,000 km2. It has a 7,300-km coastline and more than 60 inhabited smaller islands with no road connection to the mainland. The country is divided into 5 regions with a total population of approximately 5.8 million.

      Danmarks Statistik. 2020. Available at: https://www.dst.dk/da. Accessed 10 February 2021.

      Each region is responsible for its own EMS, including emergency medical dispatch centers (EMDCs). The Danish health care system is completely tax funded and free of charge at the point of contact.
      The Danish EMS is 3-tiered and consists of ambulances operated by emergency medical providers with varying levels of training (from basic to paramedic training); ground-based critical care teams consisting of a paramedic or a consultant anesthesiologist or a paramedic critical care team depending on the regional setup; and helicopter-based critical care teams that consist of an experienced consultant anesthesiologist, a pilot, and a specially trained HEMS paramedic.
      Both the air-based and ground-based EMS units are dispatched by 1 of the 5 EMDCs. These centers are staffed with health care professionals (eg, specially trained nurses and paramedics) and handle all the emergency calls through the European emergency number 1-1-2. The health care professionals assess the urgency and the appropriate EMS response for the emergency by using a systematic caller interview supported by a criteria-based dispatch protocol (Danish Index).
      • Andersen MS
      • Johnsen SP
      • Sørensen JN
      • Jepsen SB
      • Hansen JB
      • Christensen EF
      Implementing a nationwide criteria-based emergency medical dispatch system: a register-based follow-up study.
      ,
      • Præhospitalet RM
      Dansk Index for akuthjælp.
      The EMDCs and EMS system in Denmark have been described in further detail elsewhere.
      • Alstrup K
      • Møller TP
      • Knudsen L
      • et al.
      Characteristics of patients treated by the Danish Helicopter Emergency Medical Service from 2014-2018: a nationwide population-based study.
      ,
      • Andersen MS
      • Johnsen SP
      • Sørensen JN
      • Jepsen SB
      • Hansen JB
      • Christensen EF
      Implementing a nationwide criteria-based emergency medical dispatch system: a register-based follow-up study.
      ,
      • Andersen MS
      • Carlsen HP
      • Christensen EF
      Criteria-based emergency medical dispatch of ambulances fulfils goals.
      ,
      • Rognas L
      • Hansen TM
      • Kirkegaard H
      • Tønnesen E
      Pre-hospital advanced airway management by experienced anaesthesiologists: a prospective descriptive study.
      HEMS in Denmark is available 24 hours a day 7 days a week, and the service covers the entire country. The Danish HEMS operates identical EC 135 P3 Airbus helicopters equipped and certified for flying under visual and instrument flight rules using point-in-space navigation if necessary day and night. During the study period, 3 aircraft were operating from 3 bases located in Ringsted, Billund, and Skive. Since January 1, 2019, the service has been expanded by an additional helicopter based in Aalborg.
      After each HEMS mission, patient- and mission-related data are registered in the national Danish HEMS database.
      • Alstrup K
      • Petersen JA
      • Barfod C
      • Knudsen L
      • Rognås
      • Møller TP
      The Danish helicopter emergency medical service database: high quality data with great potential.
      The HEMS physicians are responsible for the data registration. The HEMS missions are divided into 4 categories: patients escorted to the hospital by HEMS either by air or road, patients assisted on scene but not escorted to the hospital by HEMS, aborted missions (defined as missions canceled in-flight before reaching the scene), and rejected missions (defined as missions where takeoff from base did not occur). In addition, telephone inquiries that do not result in a mission are registered separately.

       HEMS Dispatch Criteria

      HEMS dispatch can be based on an immediate response to a 1-1-2 call (eg, cardiac arrest, stroke, or major trauma), a crew request from the scene, interhospital transfers, and noncritical missions to areas where access by ground transport is not feasible (eg, a smaller island without road connection to the mainland).
      Primary HEMS missions include immediate dispatches, crew requests, and island missions, and the secondary missions include interhospital transfers. A detailed description of the dispatch criteria has previously been described.
      • Alstrup K
      • Møller TP
      • Knudsen L
      • et al.
      Characteristics of patients treated by the Danish Helicopter Emergency Medical Service from 2014-2018: a nationwide population-based study.
      HEMS is infrequently dispatched to the more urban areas or areas close to 1 of the 4 university hospitals.

       Selection of Participants

      The study included all primary HEMS missions with a patient encounter. Thus, missions resulting in a patient being air lifted, assisted, or ground escorted by HEMS were analyzed. Aborted and rejected missions as well as interhospital transfers, island missions, and telephone inquiries not leading to a mission were excluded from the study.
      Missions with registration errors, missions with a missing or incomplete civil registration system (CRS) number, and missions in which more than 2 CRS numbers were reported from the same mission were also excluded from the study. Missing data were not substituted.

       Data Sources and Variables

      We retrieved data from 3 national patient registries: the Danish HEMS database; the Danish Civil Registration System, which contains daily updated vital status for all Danish residents; and the Danish National Patient Register (DNPR), comprising data from all in- and outpatient hospital contacts.
      From the Danish HEMS database, we retrieved the National Advisory Committee for Aeronautics (NACA) score and prehospital critical care interventions. The NACA score is an 8-level severity scoring system ranging from 0 (no injury or disease) to 7 (death) widely used in European prehospital systems to describe the severity of the patient's illness or injury.
      • Raatiniemi L
      • Mikkelsen K
      • Fredriksen K
      • Wisbord T
      Do pre-hospital anaesthesiologists reliably predict mortality using the NACA severity score? A retrospective cohort study.
      In Supplemental Table S1, the definition of each score is presented. Studies have demonstrated the NACA score's ability to predict in-hospital mortality and the need for respiratory assistance.
      • Raatiniemi L
      • Mikkelsen K
      • Fredriksen K
      • Wisbord T
      Do pre-hospital anaesthesiologists reliably predict mortality using the NACA severity score? A retrospective cohort study.
      • Bonatti J
      • Göschl Larcher P
      • Wödlinger R
      • Flora G
      Predictors of short-term survival after helicopter rescue.
      • Weiss M
      • Bernoulli L
      • Zollinger A
      [The NACA scale. Construct and predictive validity of the NACA scale for prehospital severity rating in trauma patients].
      Even though the NACA score is widespread in its use, there is, to our knowledge, no consensus on a cutoff regarding an emergency condition. Based on the definition of each of the scores in the 8-scale score, we have found it reasonable to consider an NACA score of 4, 5, 6, or 7 to represent a patient in a critical condition corresponding to a severe or critical illness or injury. Thus, the NACA score was divided into 2 categories: scores of 0 to 3 were considered a noncritical emergency, and scores of 4 to 7 were considered a critical emergency.
      Critical care interventions performed by the HEMS team on scene included endotracheal intubation, pleural drainage (chest tube placement and thoracostomy), an automated chest compression device, intraosseous access, prehospital use of blood products, and ultrasound examination. The ultrasound examination was included as a critical care intervention because it may impact the treatment and triage on scene by distinguishing between or ruling out specific emergency conditions. From the Danish Civil Registration System, we retrieved data on the mortality.
      From the DNPR, we retrieved information regarding hospitalization history, admittance to the intensive care unit (ICU), mechanical ventilation, and total length of hospital stay (LOS). We also retrieved data on patient comorbidities before their HEMS encounter represented by the Charlson Comorbidity Index (CCI). The index was based on the International Classification of Diseases, Tenth Revision diagnosis retrieved from the DNPR 10 years back in time from the date of the alarm leading to the dispatch of the HEMS. The CCI was divided into 4 groups; CCI 0, CCI 1 to 2, CCI 3 to 4, and CCI 5 or above. Lastly, we retrieved the first specified International Classification of Diseases, Tenth Revision diagnosis assigned to the patient during the hospital stay.

       Outcomes

      The outcomes included the NACA score; the critical care interventions performed; whether the patients were referred to a university hospital versus a district general hospital; whether the patients were admitted to the ICU; whether the patients were treated with mechanical ventilation; LOS; and mortality rates at day 1 (defined as death on the day or the day after the dispatch of HEMS), day 30, and after 1 year.

       Statistical Analysis

      We characterized the study population by using descriptive statistics and report categoric variables in numbers and frequencies, whereas continuous variables are provided in medians with the interquartile range (IQR). We present mortality as the cumulative mortality at day 1, day 30, and day 365 with the 95% confidence interval. The analyses were performed in the Stata statistical program (Stata Statistical Software Version 15.1; StataCorp, College Station, TX).

      Results

      A total of 13,391 HEMS entries were registered in the database during the study period. The inclusion of the patients is illustrated in the flowchart in Figure 1. There was an equal distribution between the 3 HEMS bases, each accounting for one third of the dispatches.
      Figure 1
      Figure 1A flowchart showing the inclusion of the patients.
      Telephone inquiries (n = 180) were excluded. In 3,630 cases, the HEMS mission was aborted, 1,699 HEMS missions were rejected, and 749 missions were classified as interhospital transfers. These missions were excluded from the analyses.
      Thus, 7,133 HEMS missions were classified as a primary mission with a patient encounter. Island missions (n = 1,184), missions with registration errors (n = 16), missions with a missing or incomplete CRS number (n = 397), and missions in which more than 2 CRS numbers were reported from the same mission (n = 12) were also excluded, leaving 5,524 primary missions for further analysis. There were 1,319 trauma cases and 4,205 nontrauma cases. Among the 5,524 patients, 502 patients were declared dead on scene, and 108 patients were discharged from the scene. In 18 missions, the data on hospital destination were missing. Thus, no hospitalization history regarding these 628 patients was registered in the DNPR.
      We present the demographics of the study population in Table 1. In total, 68% of the patient population was men. This distribution was about the same for both the trauma and the nontrauma group.
      Table 1Demographics and Comorbidities for Trauma and Nontrauma Patients (N = 5,524)
      Trauma Patients

      (n = 1,319)
      Nontrauma Patients

      (n = 4,205)
      Total

      (N = 5,524)
      Sex
       Male, n (%)919 (70)2,823 (67)3,742 (68)
       Female, n (%)400 (30)1,382 (33)1,782 (32)
      Age
       Median (IQR)38 (21-56)63 (50-73)59 (41-71)
       < 1 month, n (%)2 (0.2)16 (0.4)18 (0.3)
       1 month to 1 year, n (%)22 (2)115 (3)137 (2)
       2-17 years, n (%)198 (15)174 (4)372 (7)
       18-66 years, n (%)905 (69)2,113 (50)3,018 (55)
       67+ years, n (%)192 (15)1,787 (42)1,979 (36)
      Comorbidities
       CCI groups
        0, n (%)1,082 (82)2,436 (58)3,518 (64)
        1-2, n (%)190 (14)1,080 (26)1,270 (23)
        3-4, n (%)31 (2)394 (9)425 (8)
        5 or above, n (%)16 (1)295 (7)311 (6)
       Specific diagnoses (weight
      Weight in the Charlson Comorbidity Index for selected diagnoses.
      )
        Acute myocardial infarction (1), n (%)23 (2)284 (7)307 (6)
        Congestive heart failure (1), n (%)13 (1)297 (7)310 (6)
        Peripheral vascular disease (1), n (%)27 (2)326 (8)353 (6)
        Cerebral vascular disease (1), n (%)34 (3)459 (11)493 (9)
        Chronic pulmonary disease (1), n (%)63 (5)400 (10)463 (8)
        Ulcer disease (1), n (%)17 (1)116 (3)133 (2)
        Diabetes (2), n (%)47 (4)525 (13)572 (10)
        Moderate to severe renal disease (2), n (%)13 (1)171 (4)184 (3)
        Any cancer, n (%)49 (4)450 (11)499 (9)
      CCI = Charlson Comorbidity Index; IQR = interquartile range.
      a Weight in the Charlson Comorbidity Index for selected diagnoses.
      The patient age ranged from 0 to 99 years with an overall median age of 59 years (IQR, 41-71 years). For the trauma patients, the median age was 38 years (IQR, 21-56 years), and for the nontrauma patients, the median age was 63 years (IQR, 50-73 years).
      It further appears that 64% of the study population had a CCI of 0. A higher proportion of the trauma patients (82%) had a CCI of 0 compared with the nontrauma patients (58%). Chronic pulmonary disease and cancer were the most common comorbidities among the trauma patients, whereas diabetes followed by cerebral vascular disease were the most common comorbidities among the nontrauma patients. In Supplemental Table S2, the weight of all the specific diagnoses in the CCI and the distribution of these among the patients are displayed.

       Severity Score, Interventions, Hospitalization, and Mortality

      Table 2 presents the distribution of the NACA score and the critical care interventions performed as well as the clinical course in the hospital (secondary outcomes). The most applied NACA score in the trauma group was 3 (37%). This differs from the nontrauma group in which the most applied NACA score was 4 (36%).
      Table 2The Distribution of the National Advisory Committee for Aeronautics (NACA) Score and Interventions Performed, the Clinical Course in the Hospital, and Unadjusted Cumulative Mortality for Trauma and Nontrauma Patients (N = 5,524)
      Trauma Patients

      (n = 1,319)
      Nontrauma Patients

      (n = 4,205)
      Total

      (N = 5,524)
      NACA score, n (%)
      Missing NACA score for 4 patients, 2 in the trauma group and 2 in the nontrauma group.
       NACA 03 (0.2)5 (0.1)8 (0.1)
       NACA 129 (2)46 (1)75 (1)
       NACA 2156 (12)174 (4)330 (6)
       NACA 3482 (37)945 (23)1,427 (26)
       NACA 4383 (29)1,516 (36)1,899 (34)
       NACA 5130 (10)494 (12)624 (11)
       NACA 681 (6)516 (12)597 (11)
       NACA 755 (4)505 (12)560 (10)
      NACA score, noncritical vs. critical, n (%)
       NACA 0-3649 (49)1,174 (28)1,823 (33)
       NACA 4-7670 (51)3,031 (72)3,701 (67)
      Interventions, n (%)
       Intubation281 (21)984 (23)1,265 (23)
        by HEMS181 (64)585 (59)766 (61)
        by other100 (36)399 (41)499 (39)
       Blood administration115 (9)51 (1)166 (3)
       Intraosseous access68 (5)344 (8)412 (8)
       ACCD25 (2)427 (10)452 (8)
       Ultrasound examination475 (36)844 (20)1,319 (24)
       Chest tube/thoracostomy64 (5)42 (1)106 (2)
      At least 1 intervention performed, n (%)645 (49)1,771 (42)2,416 (44)
      Hospital stay, n (%)
       University hospital757 (57)2,293 (55)3,050 (55)
       Regional hospital486 (37)1,360 (32)1,846 (33)
       Secondary transfer < 24 hours9 (1)37 (1)46 (1)
       Secondary transfer during hospitalization, n (%)70 (5)297 (7)367 (7)
       Missing hospital destination, n (%)73 (6)537 (13)610 (11)
       Declared dead on scene, n (%)48 (4)454 (11)502 (9)
       Discharged from scene, n (%)25 (2)83 (2)108 (2)
      ICU stay, n (%)
       Admittance389 (30)796 (19)1,185 (22)
       Mechanical ventilatory treatment203 (52)556 (70)759 (14)
      Length of stay (IQR)
       Median days2 (0-10)3 (0-7)3 (0-8)
      Unadjusted cumulative mortality, % (95% CI)
       Cumulative mortality, day 17 (6.1-8.9)19 (17.6-19.9)
       Cumulative mortality, day 3011 (9.1-12.5)26 (24.2-26.9)
       Cumulative mortality, day 36512 (10.2-13.7)30 (28.4-31.1)
      ACCD = automated chest compression device; CI = confidence interval; HEMS = helicopter emergency medical services; ICU = intensive care unit; IQR = interquartile range
      a Missing NACA score for 4 patients, 2 in the trauma group and 2 in the nontrauma group.
      A higher proportion of the patients in the nontrauma group (72%) were classified as having a critical emergency (NACA 4-7) compared with the trauma patients (51%).
      At least 1 critical care intervention was performed in 49% of the trauma cases and 42% of the nontrauma cases. The distribution of critical care interventions is illustrated in Figure 2. The most frequently performed critical care interventions in the trauma group were ultrasound examination (36%) and intubation (21%) followed by the administration of blood products (9%). This differed from the nontrauma group in which 23% were intubated, 20% had an ultrasound examination, and 10% were treated with an automated chest compression device. Few (1%) were administered blood.
      Figure 2
      Figure 2The distribution of the critical care interventions according to the patient group. ETI = endotracheal intubation, IO = intraosseous access; ACCD = automated chest compression device; US = ultrasound examination; PD = pleural drainage (chest tube/thoracostomy).
      The majority of both the trauma patients (57%) and the nontrauma patients (55%) were brought to a university hospital. The number of patients brought to a regional hospital and then secondarily transferred to a university hospital within 24 hours was low in both patient groups (1%). The proportion of secondary transfers to a university hospital during the entire hospitalization stay was higher among the nontrauma patients (7%) compared with the trauma patients (5%).
      The proportion of trauma patients admitted to the ICU was 30% compared with 19% among the nontrauma patients. However, fewer patients in the trauma group (52%) were subsequently in need of mechanical ventilation compared with 70% of the nontrauma patients. The median LOS was 2 days (IQR, 0-10 days) for trauma patients and 3 days (IQR, 0-7 days) for nontrauma patients.
      Table 2 also presents the cumulative mortality for both the trauma patients and the nontrauma patients. The highest mortality at all times was observed in the nontrauma group.

      Discussion

      To our knowledge, this is the first nationwide register-based study reporting patient demographics, hospitalization, and mortality in trauma and nontrauma HEMS patients. We found that a higher proportion of patients in the nontrauma group were classified as having a critical emergency (NACA 4-7). However, a slightly higher proportion of the trauma patients had at least 1 critical care intervention performed, and more trauma patients were admitted to the ICU and needed mechanical ventilation compared with nontrauma patients.
      We also found a lower mortality among trauma patients compared with nontrauma patients.
      A lower mortality among trauma HEMS patients has been found in other studies as well.
      • Raatiniemi L
      • Mikkelsen K
      • Fredriksen K
      • Wisbord T
      Do pre-hospital anaesthesiologists reliably predict mortality using the NACA severity score? A retrospective cohort study.
      ,
      • Bonatti J
      • Göschl Larcher P
      • Wödlinger R
      • Flora G
      Predictors of short-term survival after helicopter rescue.
      In the study by Raatiniemi et al,
      • Raatiniemi L
      • Mikkelsen K
      • Fredriksen K
      • Wisbord T
      Do pre-hospital anaesthesiologists reliably predict mortality using the NACA severity score? A retrospective cohort study.
      a significantly higher 30-day mortality was found in the nontrauma group, and in the study by Bonnati et al,
      • Bonatti J
      • Göschl Larcher P
      • Wödlinger R
      • Flora G
      Predictors of short-term survival after helicopter rescue.
      they showed a statistically significant difference between various types of injuries and medical and neurologic emergencies.
      The patients in the trauma group in our study were younger than the patients in the nontrauma group, and they also suffered less from chronic illnesses than did the patients in the nontrauma group. This could be 1 possible explanation of the lower mortality in the trauma patient group compared with the nontrauma patients. Furthermore, a higher proportion of patients in the nontrauma group were classified as having a critical emergency (NACA 4-7) compared with the trauma patients. This could also explain the difference in mortality observed in our study and is in line with results from a study by Bonatti et al
      • Bonatti J
      • Göschl Larcher P
      • Wödlinger R
      • Flora G
      Predictors of short-term survival after helicopter rescue.
      in which the authors concluded that the severity of a patient's emergency condition classified by the NACA score was strongly associated with short-term survival.
      Despite a lower mortality rate in the trauma patient group compared with the nontrauma patient group, a higher proportion of trauma patients received a least 1 critical care intervention. This could partly be explained by the higher proportion of ultrasound examinations performed among the trauma group (36%) compared with the nontrauma patients (20%). Also, we found that slightly more patients in the trauma group were escorted to a university hospital, and they were more often admitted to the ICU compared with the nontrauma patient group. This could suggest that these patients often were in a potentially critical condition, although this was not reflected by an increased LOS. The reduced LOS among the trauma patients compared with the nontrauma patients could perhaps be explained by their younger age and their lower degree of comorbidities. In a Danish single-center study reporting data from 1 ground-based physician-staffed critical care unit, it was concluded that mortality was associated with age and comorbidity (defined by increasing CCI) as well as time spent at the hospital.
      • Mikkelsen S
      • Lossius HM
      • Toft P
      • Lassen AT
      Characteristics and prognoses of patients treated by an anaesthesiologist-manned prehospital emergency care unit. A retrospective cohort study.
      The performance of a critical care intervention has been suggested as a proxy marker for HEMS mission relevance.
      • Munro S
      • Joy M
      • de Coverly R
      • Salmon M
      • Williams J
      • Lyon RM
      A novel method of non-clinical dispatch is associated with a higher rate of critical helicopter emergency medical service intervention.
      In a recent Scottish study, the authors found that 42% of the HEMS missions were appropriately tasked when the evaluation was based on the performed critical care interventions.
      • Neagle G
      • Curatolo L
      • Ferris J
      • Donald M
      • Hearns S
      • Corfield AR
      Epidemiology and location of primary retrieval missions in a Scottish aeromedical service.
      Although definitions may differ, this is in line with our results. Nevertheless, it should be noted that critical care interventions may not be suitable as the only proxy marker for proper HEMS tasking because many other factors may impact triage decisions.
      Our results could also indicate that there may be a different threshold for dispatching HEMS to nontrauma cases compared with trauma cases, which has been suggested elsewhere.
      • Østerås Ø
      • Brattebø G
      • Heltne JK
      Helicopter-based emergency medical services for a sparsely populated region: a study of 42,500 dispatches.
      The observed difference in mortality could partly reflect a different way of dispatching HEMS in case of suspected trauma compared with the dispatch strategy in case of suspected medical condition. The decision to dispatch the HEMS team to trauma cases is often based on the mechanism of injury (eg, high-energy trauma or person trapped) and, if possible, the patient's clinical condition. In contrast, the dispatch decision in suspected medical cases is primarily based on the patient's chief complaints and medical history. The mechanism of injury–based strategy may be used to minimize undertriage (“benefit of the doubt”). However, this approach seems to contribute to overtriage because it considers the risk of being injured instead of an attempt to identify the actual severely injured patients.
      • Brown JB
      • Stassen NA
      • Bankey PE
      • Sangosanya AT
      • Cheng JD
      • Gestring ML
      Mechanism of injury and special consideration criteria still matter: an evaluation of the National Trauma Triage Protocol.
      ,
      • Haider AH
      • Chang DC
      • Haut ER
      • Cornwell 3rd, EE
      • Efron DT
      Mechanism of injury predicts patient mortality and impairment after blunt trauma.
      In summary, adequate HEMS dispatch is a complex task and relies primarily on a shared understanding of the emergency condition between the caller and the dispatching staff, ideally working on the basis of a validated dispatch tool. Our findings suggest a review of the current guidelines and ongoing efforts into the education of triaging staff seem of importance for the appropriate use of HEMS.

       Strengths and Limitations

      An important strength of this study is its nationwide population-based design including data from all HEMS units operating during the study period. Furthermore, the registries used in the study are considered of high quality including a high degree of data completeness.
      • Alstrup K
      • Petersen JA
      • Barfod C
      • Knudsen L
      • Rognås
      • Møller TP
      The Danish helicopter emergency medical service database: high quality data with great potential.
      ,
      • Schmidt M
      • Schmidt SA
      • Sandegaard JL
      • Ehrenstein V
      • Pedersen L
      • Sørensen HT
      The Danish National Patient Registry: a review of content, data quality, and research potential.
      ,
      • Mainz J
      • Hess MH
      • Johnsen SP
      The Danish unique personal identifier and the Danish Civil Registration System as a tool for research and quality improvement.
      This study also has some limitations. One is the observational study design. Moreover, the assessment of prehospital patients is a complex task and may be influenced by multiple factors; therefore, interrater variability is inevitable. This especially applies for the NACA score.
      Another limitation is the lack of information caused by missing CRSs. This can bias the results because the missing data can represent patients either more or less critically ill/injured than those with a registered CRS. Also, we did not have the opportunity to assess possible preventable deaths or follow-up on patients discharged from the scene, although such an evaluation could add valuable knowledge about the on-scene treatment, decision making, and triage. Lastly, because the study included highly specialized prehospital critical care teams, the study's generalizability may be limited to other HEMS with similar staffing, settings, and case mix.

       Perspective and Future Studies

      This study is 1 of the very few to compare 2 patient groups in a complete national HEMS population, and, therefore, the results may add considerable knowledge to the existing literature. Improving our knowledge of the Danish HEMS population is important to optimize HEMS dispatch and use.
      Further evaluations should include an investigation of the cause of death among trauma and nontrauma patients and research into what could be the reason for the doubled mortality rate among trauma patients from day 1 to day 30. Moreover, in a small country like Denmark, immediate dispatch appears to be crucial to fully use the advantages potentially associated with HEMS. Therefore, future research using live video footage streaming from the scene via smartphone, as tested feasible in a recent English study,
      • Ter Avest E
      • Lambert E
      • de Coverly R
      • et al.
      Live video footage from scene to aid helicopter emergency medical service dispatch: a feasibility study.
      could add to the complex understanding of HEMS dispatch.
      The suggested overtriage of HEMS to minor trauma cases could imply that the dispatch criteria based on the mechanism of injury may be imprecise, especially as safety technologies in vehicles are developed and updated continuously. Thus, the dispatch criteria may deserve a thorough evaluation in order to improve the use of HEMS even further.

      Conclusion

      This national study demonstrated that the trauma patients were younger, had a lower degree of comorbidity, and a lower proportion of critical emergencies, as well as a lower mortality. However, slightly more trauma patients were escorted to a university hospital, and they were more often in need of ICU treatment, although this was not reflected by a longer hospital stay.
      The different demographic profile, hospital course, and mortality could partly reflect differences in thresholds for HEMS tasking for trauma patients compared with nontrauma patients, suggesting that educational efforts and a review of the current dispatching guidelines could be of importance when trying to improve the use of HEMS in Denmark.

      Appendix. Supplementary materials

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