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Secondary Transfers to University Hospitals in Patients Primarily Triaged to District General Hospitals by the Danish Helicopter Emergency Medical Service: A National Population-Based Study

Open AccessPublished:October 08, 2021DOI:https://doi.org/10.1016/j.amj.2021.08.009

      Highlights

      • Patients initially triaged to a district general hospital by the helicopter emergency medicalc services (HEMS) team seldomly required a secondary transfer to a university hospital within 24 hours from the initial emergency call.
      • Cardiovascular and neurologic emergencies were the major reasons for transportation.
      • Mortality among these patients seems comparable to that in the general population of patients treated by the Danish HEMS teams.

      Abstract

      Objective

      The aim of this study was to analyze data from the Danish helicopter emergency medical service (HEMS) database, focusing on patients undergoing a secondary transfer from district general hospitals (DGHs) to university hospitals within 24 hours of the initial emergency call.

      Methods

      This is a national population-based study analyzing HEMS patients undergoing a secondary transfer between October 1, 2014, and April 30, 2018.

      Results

      Fifty-three (2.9%) of the 1,846 patients initially triaged to a DGH by the HEMS team required a secondary transfer. These 53 patients constituted 0.7% of all 7,133 patients seen by the HEMS teams during the study period. More than 60% of these patients were initially treated for either a cardiovascular or a neurologic emergency. HEMS-escorted patients had a mortality rate at day 30 of 14.3% (95% confidence interval, 4.8-38.0), and the HEMS-assisted group had a mortality rate at day 30 of 3.1% (95% CI, 0.5-20.2).

      Conclusion

      Patients initially triaged to a DGH by the HEMS teams seldomly required a secondary transfer, indicating a low degree of prehospital undertriage for direct transfer to a university hospital. Cardiovascular or neurologic emergencies were the major reasons for transportation. Mortality seems comparable with that in the general population of patients treated by the Danish HEMS teams.
      The Danish helicopter emergency medical service (HEMS) was introduced as a nationwide service on October 1, 2014, after a recommendation from the Danish Health Department.

      Enhanced emergency preparedness - planning basis for the regional health service. Available at: https://www.sst.dk/da/udgivelser/2007/styrket-akutberedskab–planlaegningsgrundlag-for-det-regionale-sundhedsvaesen. Accessed June 1, 2021.

      HEMS is a supplement to the Danish ground-based emergency medical service (EMS), aiming to 1) ensure physician-led prehospital critical care for patients regardless of their location, 2) provide rapid transport of patients from the incident scene to the most relevant hospital, and 3) provide safe and rapid interhospital transport of critically ill patients. The specialized medical team offers expert critical care on scene and a highly skilled physician-led triage of the patients to either a university hospital or a district general hospital (DGH) depending on the extent and the character of the patient's injury or illness.
      Research has shown that on-site triage of patients is a difficult and complex task.
      • Rehn M
      • Eken T
      • Krüger AJ
      • Steen PA
      • Skaga NO
      • Lossius HM.
      Precision of field triage in patients brought to a trauma centre after introducing trauma team activation guidelines.
      Undertriage may potentially delay crucial medical treatment, potentially resulting in an increased risk of adverse outcomes. On the other hand, overtriage of patients may cause unnecessary use of medical resources like HEMS and university hospital capacity.
      A recent article using data from the Danish HEMS database highlighted that 53% of HEMS dispatches resulted in a primary mission with a patient encounter.
      • 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.
      Of these, 67% were escorted to either a DGH or a university hospital by the HEMS team (HEMS-escorted patients), and 33% were treated on scene and either discharged or escorted to the hospital by the ground EMS alone (HEMS-assisted patients). Furthermore, in another recent article, we showed that a small proportion of patients primarily triaged to a DGH were secondarily transferred to a university hospital.
      • Alstrup K
      • Petersen JAK
      • Sollid S
      • Johnsen SP
      • Rognås L
      Mortality and hospitalisation in the Danish helicopter emergency medical service (HEMS) population from 2014 to 2018: a national population-based study of HEMS triage.
      The characteristics of these patients are unknown.
      The aim of this study was to describe patient characteristics in terms of demographics, comorbidity, severity of illness/injury, prehospital diagnostic group, and mortality in HEMS-escorted and HEMS-assisted patients primarily triaged to a DGH by the HEMS team but subsequently undergoing a secondary transfer to a university hospital within the first 24 hours after the initial 112 call and HEMS dispatch. Furthermore, the study aimed to describe the first International Statistical Classification of Diseases, 10th Revision (ICD-10) diagnosis assigned at the DGH and at the university hospital.

      Methods

      Study Design

      The current study is a descriptive population-based study presenting data from the national Danish HEMS database. The study included patients registered in the database from October 1, 2014, to April 30, 2018. According to the Central Denmark Region Committee on Health Research Ethics, no ethical approval was needed for the study (j.nr.: 1-10-72-4-17).

      Setting

      Denmark is a mixed urban and rural country located in northern Europe with a total areal of 42.931 km2 and approximately 5.8 million inhabitants. It has a long coastline and more than 70 islands without road connection to the mainland. The Danish health care system is publicly funded and free of charge at the point of access. Both pre- and in-hospital emergency care are available for both Danish citizens and noncitizens alike.
      • Lindskou TA
      • Mikkelsen S
      • Christensen EF
      • et al.
      The Danish prehospital emergency healthcare system and research possibilities.
      The country consists of 5 regions, each with its own prehospital organization responsible for EMS. All medical calls to the European emergency phone number 1-1-2 will lead to direct contact with the police or the fire brigade, who forwards the call to a regional emergency medical dispatch center.
      • 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.
      Medical call takers (ie, paramedics and nurses) assess the severity of the patient condition and provide guidance to the caller using the Danish Index for Emergency Care,
      • 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.
      , a Danish flowchart-based emergency medical dispatch center triage tool. This index is used in all Danish regions.
      • 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.
      Dedicated emergency dispatchers then task the different prehospital units.
      EMS field services consist of ground ambulances, ground-based prehospital critical care teams (with an anesthesiologist and a paramedic/emergency medical technician), and currently 4 HEMS teams.
      • 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.
      Each HEMS team is composed of a pilot, a specially educated HEMS paramedic, and a consultant anesthesiologist.

      Available at: https://www.akutlaegehelikopter.dk. Accessed June 1, 2021.

      In the study period, 3 HEMS units were operating from 3 sites in Denmark with an around-the-clock specialized medical service.

      Available at: https://www.akutlaegehelikopter.dk. Accessed June 1, 2021.

      The initiation of a HEMS mission can either be 1) an immediate dispatch based on the 1-1-2 call, 2) a crew request from the scene, 3) an interhospital transfer, and 4) missions to smaller islands not connected to the mainland. Interhospital transfers are characterized as secondary transfers. The remaining HEMS dispatch criteria are considered primary transfers.
      • 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.
      ,

      Available at: https://www.akutlaegehelikopter.dk. Accessed June 1, 2021.

      HEMS missions are divided into 5 categories: airlifted patients, ground-escorted patients, assisted patients, aborted missions (also known as stand-downs, most often due to information from the scene identifying that there is no need for HEMS), and rejected missions.
      • 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.
      Definitions of each patient group are shown in Table 1. The current study included airlifted, ground-escorted, and assisted patients. Airlifted and ground-escorted patients are referred to as “HEMS escorted,” and patients assisted on scene but not escorted to the hospital by the HEMS team are referred to as “HEMS assisted” in the following.
      Table 1The definition of each type of mission
      Air lifted patientsMissions where the HEMS physician escorted the patient in the helicopter to the hospital
      Ground escorted patientsMissions where the HEMS physician escorted the patient in an ambulance to the hospital
      Assisted patientsMissions where HEMS attended the patient and assisted the ground crew (ambulance and RRV) but did not escort the patient
      Aborted missionsMissions cancelled in-flight before reaching the scene
      Rejected missionsMissions where take-off from the base did not occur

      Selection of Participants

      The study included all primary HEMS missions with patients encountered by the HEMS team triaged to a DGH and secondarily transferred to a university hospital within the first 24 hours of the initial 1-1-2 call.
      Patients for whom a secondary transfer from a DGH to a university hospital was undertaken more than 24 hours after the 1-1-2 call as well as patients without or with an incomplete Danish Civil Registration System (DCRS) number were excluded from the study.

      Data Source and Variables

      Data were retrieved from 3 national patient registries including the Danish HEMS database, the DCRS, and the Danish National Patient Register.
      The HEMS database has been extensively described in a recent study.
      • Alstrup K
      • Kølsen Petersen JA
      • Barfod C
      • Knudsen L
      • Rognås L
      • Møller TP
      The Danish helicopter emergency medical service database: high quality data with great potential.
      It provides patient and/or operational information from all HEMS dispatches. From this database, we retrieved information on the mission type and the severity of illness/injury evaluated using the National Advisory Committee for Aeronautics (NACA) score modified for prehospital use assigned each patient on scene.
      • Weiss M
      • Bernoulli L
      • Zollinger A.
      [The NACA scale. Construct and predictive validity of the NACA scale for prehospital severity rating in trauma patients].
      ,
      • Darioli V
      • Taffé P
      • Carron P-N
      • et al.
      Evaluation of the discriminative performance of the prehospital National Advisory Committee for Aeronautics score regarding 48-h mortality.
      It is an 8-level subjective score ranging from 0 (no injury or disease) to 7 (death); please refer to Supplementary Table S1 for a definition of each score. Based on these definitions, we found it reasonable to divide the score into 2 categories; we considered NACA 0 to 3 as a noncritical emergency and NACA 4 to 7 as representing a (potentially) critical emergency. We also retrieved data on the prehospital diagnostic group assigned by the attending HEMS physician (“cardiovascular,” “neurology,” “trauma,” “respiratory,” “abdominal,” and “other medical conditions”).
      The DCRS contains continuously updated vital status and place of residence for all Danish residents.
      • Pedersen CB.
      The Danish Civil Registration System.
      We retrieved data regarding mortality from the DCRS.
      The Danish National Patient Register is a population-based administrative registry. It includes both administrative and patient-related data on all in-hospital as well as outpatient activity.
      • Lynge E
      • Sandegaard JL
      • Rebolj M.
      The Danish National Patient Register.
      From this registry, we obtained information on patient demography (sex and age) and comorbidity evaluated by the Charlson Comorbidity Index (CCI).
      • Charlson ME
      • Pompei P
      • Ales KL
      • MacKenzie CR.
      A new method of classifying prognostic comorbidity in longitudinal studies: development and validation.
      • Bannay A
      • Chaignot C
      • Blotière P-O
      • et al.
      The best use of the Charlson Comorbidity Index with electronic health care database to predict mortality.
      • Thygesen SK
      • Christiansen CF
      • Christensen S
      • Lash TL
      • Sørensen HT.
      The predictive value of ICD-10 diagnostic coding used to assess Charlson comorbidity index conditions in the population-based Danish National Registry of Patients.
      The CCI was divided into 4 groups: CCI 0, CCI 1 to 2, CCI 3 to 4, and CCI 5 or above.
      We further obtained data on the first assigned ICD-10 diagnoses at the DGH and the university hospital as classified by the Danish version of the World Health Organization's ICD-10
      • Lynge E
      • Sandegaard JL
      • Rebolj M.
      The Danish National Patient Register.
      ,

      World Health Organization. International Statistical Classification of Diseases and Related Health Problems, 10th Revision. Available at: https://icd.who.int/browse10/2016/en. Accessed June 1, 2021.

      ; the primary hospital destination, which was defined as the first hospital receiving the patient from the HEMS or the ambulance (DGH or university hospital); and secondary transfers to a university hospital within 24 hours from the 112 alarm.
      The DCRS number assigned each Danish individual at birth is a 10-digit unique personal identification number used in all Danish registries. We used the DCRS number to link data from the 3 registries.

      Outcomes

      Study outcomes included the percentage of patients initially seen by the HEMS teams and primarily triaged to a DGH but secondarily transferred from the DGH to a university hospital within 24 hours of the initial 1-1-2 call, the NACA score, the prehospital diagnostic group assigned by the HEMS physician, the first ICD-10 diagnosis assigned at the DGH and the university hospital, and mortality rates at day 30 and 365.

      Statistical Analyses

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

      Results

      The inclusion of patients is shown in Figure 1. During the study period, a total of 13,391 HEMS entries were registered in the HEMS database. Of these, 13,211 led to a HEMS dispatch, and 7,133 resulted in a primary HEMS mission with a patient encounter. The remaining dispatches were aborted missions (n = 3,630), rejected missions (n = 1,699), and interhospital transfers (n = 749). In total, 53 (2.9%) of the 1,846 patients initially triaged to a DGH by the HEMS team required a secondary transfer to a university hospital during the first 24 hours after the initial 1-1-2 emergency call. These 53 patients constituted 0.7% of all 7,133 patients seen by the HEMS teams during the study period. Of these 53 patients, 21 were escorted to the DGH by the HEMS team (by air or by land), and 32 were transported by ground EMS alone.
      Figure 1
      Figure 1A flowchart showing the inclusion of patients.

      Demographics and Comorbidity

      A summary of patient demographics and CCI in the group of patients secondarily transferred during the first 24 hours is shown in Table 2. The overall median age among the study population was 62 years. In the HEMS-escorted patient group, the median age was 60 years, and in the HEMS-assisted patient group, it was 63.5 years. Nearly two thirds in both patient groups were men.
      Table 2Demographics and Comorbidity for Helicopter Emergency Medical Services (HEMS)-Escorted and HEMS-Assisted Patients (N = 53)
      HEMS Escorted (n = 21)HEMS Assisted (n = 32)Total (N = 53)
      Demographics
      Sex
       Male, n (%)14 (67)20 (63)34 (64)
       Female, n (%)7 (33)12 (37)19 (36)
      Age
       Median age, years (IQR)60 (53-72)63.5 (48.5-72)62 (49-72)
       < 1 month (%)000
       0-1 year (%)000
       2-17 years (%)01 (3)1 (2)
       18-66 years (%)13 (62)18 (56)31 (58)
       > 67 years (%)8 (38)13 (41)21(40)
      Comorbidity
      CCI
       0, n (%)8 (38)19 (59)27 (51)
       1-2, n (%)7 (33)7 (22)14 (26)
       3-4, n (%)6 (29)5 (16)11 (21)
       ≥ 5, n (%)01 (3)1 (2)
      CCI = Charlson Comorbidity Index; IQR = interquartile range.
      Overall, 51% of the patients had no previous comorbidity (CCI 0). Fewer patients in the HEMS-escorted group (38%) had no comorbidity compared with 59% of patients in the HEMS-assisted group. There were more HEMS-escorted patients in the mild (CCI 1-2) and moderate (CCI 3-4) comorbidity categories compared with HEMS-assisted patients (33% vs. 22% and 29% vs. 16%, respectively).

      Severity of Illness/Injury and Prehospital Diagnostic Profile

      The distribution of NACA scores and the prehospital diagnostic groups is presented in Table 3. Overall, the most frequently used NACA score was 3 (62%) followed by a NACA score of 4 (26%). Few HEMS-escorted patients had a NACA score of 5 and 6 (14% and 10%, respectively). There were no HEMS-assisted patients with a NACA score above 4. Sixty-two percent of the HEMS-escorted patients were classified as having a critical emergency (NACA 4-7) compared with 19% of the HEMS-assisted patients.
      Table 3National Advisory Committee for Aeronautics (NACA) Score and Prehospital Diagnostic Group for Helicopter Emergency Medical Services (HEMS)-Escorted and HEMS-Assisted Patients (N = 53)
      HEMS escorted (n = 21)HEMS assisted (n = 32)Total (N = 53)
      NACA score
       0, n (%)000
       1, n (%)000
       2, n (%)01 (3)1 (2)
       3, n (%)8 (38)25 (78)33 (62)
       4, n (%)8 (38)6 (19)14 (26)
       5, n (%)3 (14)03 (6)
       6, n (%)2 (10)02 (4)
       7, n (%)000
       0-3, n (%)8 (38)26 (81)34 (64)
       4-7, n (%)13 (62)6 (19)19 (36)
      Prehospital diagnostic group
       Cardiovascular, n (%)7 (33)11 (34)18 (34)
       Neurology, n (%)7 (33)6 (18)13 (24)
       Trauma, n (%)09 (28)9 (17)
       Respiratory, n (%)4 (19)2 (6)6 (11)
       Abdominal, n (%)01 (3)1 (1)
       Other medical conditions, n (%)3 (14)3 (9)6 (11)
      The prehospital diagnostic profile differed between the 2 groups. In both groups, one third of the patients were diagnosed with a disease of the cardiovascular system. In the HEMS-escorted group, the major diagnostic categories were “neurology” (33%) and “respiratory” (19%), whereas in the HEMS-assisted group 28% of the patients were categorized as “trauma” and 18% were diagnosed within “neurology.”

      ICD-10 Diagnoses at the DGH and University Hospital

      A summary of the specific ICD-10 diagnoses assigned each patient at the DGH and the university hospital is displayed in Table 4 for HEMS-escorted patients and Table 5 for HEMS-assisted patients.
      Table 4International Statistical Classification of Diseases, 10th Revision Diagnoses at the District General Hospital (First Diagnosis) and the University Hospital (Second Diagnosis) for Helicopter Emergency Medical Services–Escorted Patients (n = 21)
      NumberFirst DiagnosisSecond Diagnosis
      1Myocardial infarction, unspecifiedMyocardial infarction, unspecified
      2Chronic obstructive pulmonary disease with exacerbation, unspecifiedChronic respiratory insufficiency
      3Cardiac arrest with successful resuscitationMyocardial infarction
      4Severe acute respiratory distress syndromeRehabilitation, unspecified
      5Cerebral hemorrhage, unspecifiedRehabilitation, unspecified
      6Unstable angina pectorisVentricular tachycardia
      7Observation for other suspected diseases and conditions, unspecifiedChronic ischaemic heart disease, unspecified
      8Cardiac lung edemaCardiac lung edema
      9Cardiac arrest with successful resuscitationChronic respiratory failure
      10Sepsis, unspecifiedGangrene
      11Cerebral haemorrhageRehabilitation, unspecified
      12Cardiac arrest with successful resuscitationCardiomyopathy, unspecified
      13Myocardial infarctionRehabilitation, unspecified
      14Cerebral hemorrhageRehabilitation, unspecified
      15Chronic obstructive pulmonary disease with acute lower respiratory infectionChronic obstructive pulmonary disease with acute lower respiratory infection
      16Observation for other suspected diseases and conditions, unspecifiedAcute vascular disorder of intestine
      17Observation for other suspected diseases and conditions, unspecifiedVentricular fibrillation and flutter
      18Sepsis, unspecifiedAbdominal abscess
      19Cerebral infarction, unspecifiedCerebral infarction due to thrombosis of precerebral arteries
      20Syncope and collapseMechanical complication of cardiac electronic device
      21Stroke, not specified as a haemorrhage or infarctionIntracranial abscess and granuloma
      Table 5International Statistical Classification of Diseases, 10th Revision Diagnoses at the District General Hospital (First Diagnosis) and the University Hospital (Second Diagnosis) for Helicopter Emergency Medical Services–Assisted Patients (n = 32)
      NumberFirst DiagnosisSecond Diagnosis
      1Chest pain, unspecifiedPneumonia due to Streptococcus pneumoniae
      2Myocardial infarction with non-ST elevation without Q-wave developmentMyocardial infarction with non-ST elevation without Q-wave development
      3Angina pectoris, unspecifiedCardiovascular disease, unspecified
      4Angina pectoris, unspecifiedAngina pectoris, unspecified
      5Observation for other suspected diseases and conditionsSubarachnoidal hemorrhage, unspecified
      6Unspecified viral encephalitisMyocardial infarction, unspecified
      7Pulmonary edema, unspecifiedMyocardial infarction with non-ST elevation without Q-wave development
      8Seizures, unspecifiedFocal idiopathic epilepsy
      9Malaise and fatigue, unspecifiedStenosis of aorta
      10Bradycardia, unspecifiedSick sinus syndrome
      11Unspecified multiple injuriesFractur of neck, part unspecified
      12Examination and observation after transport accidentAcute myocardial infarction, unspecified
      13Angina pectoris, unspecifiedAngina pectoris, unspecified
      14Observation for suspected myocardial infarctionUnstable angina pectoris
      15Myocardial infarction with non-ST elevation without Q-wave developmentAcute ischaemic heart disease, unspecified
      16Myocardial infarction with non-ST elevation without Q-wave developmentMyocardial infarction with non-ST elevation without Q-wave development
      17Syncope and collapse, unspecifiedVentricular tachycardia with ischemic heart disease
      18Chest pain, unspecifiedMyocardial infarction with non-ST elevation without Q-wave development
      19Unspecified multiple injuriesCrushing injury from unspecified fall
      20Subarachnoid hemorrhage, unspecifiedTraumatic subarachnoid hemorrhage
      21Seizure, unspecifiedHypertensive encephalopathy
      22Examination and observation after other accidentRehabilitation, unspecified
      23Examination and observation after other accidentRehabilitation, unspecified
      24Fracture of other specified cervical vertebraTraumatic rupture of cervical intervertebral disc
      25Myocardial infarction, unspecifiedRehabilitation, unspecified
      26Chronic respiratory failureRespiratory arrest
      27Examination and observation after work accidentFracture of thoracic vertebra. XI
      28Angina pectoris, unspecifiedAngina pectoris, unspecified
      29Hypoglycemia, unspecifiedOther specified diabetes with multiple complications
      30Observation for suspected myocardial infarctionOther spontaneous pneumothorax
      31Unstable angina pectorisChronic ischemic heart disease, unspecified
      32Unspecified multiple injuriesFracture of sacrum
      It appears that in the HEMS-escorted patient group, the most common diagnoses were cerebral hemorrhage, myocardial infarction, and respiratory insufficiency, whereas in the HEMS-assisted group the majority of patients were diagnosed with a myocardial infarction, angina pectoris, or a traumatic lesion.
      Supplementary Table S2 shows a summary of the different ICD-10 diagnostic chapters assigned to the 53 patients during their hospitalization at the DGH and subsequently at the university hospital.

      Mortality

      The HEMS-escorted patients had a higher cumulative mortality at day 30 and after 1 year compared with the HEMS-assisted patients (14.3% [95% CI, 4.8-38.0] and 28.6% [95% CI,14.0-53.9 vs. 3.1% [95% CI, 0.5-20.2] and 6.3% [95% CI, 1.6-22.8], respectively). Furthermore, the overall cumulative mortality after 1 year was 15.1% (95% CI, 7.9-27.9).

      Discussion

      To our knowledge, this is the first national study to report data on patient characteristics, diagnoses, and mortality in HEMS patients primarily triaged to a DGH and subsequently transferred to a university hospital within the first 24 hours after the 1-1-2 emergency call.
      Our results may indicate an appropriate on-scene triage by the HEMS physician in selecting the patients who do not need specialized treatment at a university hospital. However, the study did not investigate the number of patients who died after arrival at the DGH before a secondary transfer could be undertaken.
      It appears that only 1 patient below the age of 18 had a secondary transfer. A possible reason for this could be that there is a lack of specific pediatric expertise at DGHs; therefore, children suspected of having a severe trauma or a severe medical condition will be almost exclusively triaged to university hospitals.
      Our results show that among the patients subsequently needing a secondary transfer from a DGH to a university hospital during the first 24 hours after the initial 1-1-2 call, the HEMS physician gave a higher proportion of patients in the HEMS-escorted group a NACA score corresponding to a (potential) critical condition compared with the HEMS-assisted group. These patients also had a higher degree of chronic diseases reflected as a higher CCI. A Norwegian study by Østerås et al
      • Østerås Ø
      • Brattebø G
      • Heltne JK
      Helicopter-based emergency medical services for a sparsely populated region: a study of 42,500 dispatches.
      found that the median NACA score among the secondary transferred patients was 4, similar to our results when combining the HEMS-escorted and HEMS-assisted group. Even though our study and the Norwegian study report similar outcomes, the study by Østerås et al does not state the percentage of patients primarily transported to a DGH by HEMS and secondarily needing an interhospital transfer, making a comparison with our results difficult.
      The higher NACA score and more comorbidities among the HEMS-escorted patients were also reflected in a higher cumulative mortality rate after 30 and 365 days compared with the HEMS-assisted patients.
      In 2 recent studies describing patient characteristics and mortality for different HEMS mission types,
      • 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.
      ,
      • Alstrup K
      • Petersen JAK
      • Sollid S
      • Johnsen SP
      • Rognås L
      Mortality and hospitalisation in the Danish helicopter emergency medical service (HEMS) population from 2014 to 2018: a national population-based study of HEMS triage.
      similar findings were reported when analyzing the entire HEMS patient population.
      • Alstrup K
      • Petersen JAK
      • Sollid S
      • Johnsen SP
      • Rognås L
      Mortality and hospitalisation in the Danish helicopter emergency medical service (HEMS) population from 2014 to 2018: a national population-based study of HEMS triage.
      Christensen et al
      • Christensen EF
      • Larsen TM
      • Jensen FB
      • et al.
      Diagnosis and mortality in prehospital emergency patients transported to hospital: a population-based and registry-based cohort study.
      described mortality and diagnostic distribution among a cohort of emergency patients brought to the hospital by ambulance during the period 2007 to 2014 in the North Denmark region. The study showed mortality at day 1 and day 30 of 1.8% and 4.7%, respectively. Furthermore, the study showed that a higher CCI can be used as a predictor of mortality.
      • Christensen EF
      • Larsen TM
      • Jensen FB
      • et al.
      Diagnosis and mortality in prehospital emergency patients transported to hospital: a population-based and registry-based cohort study.
      A Danish register–based study by Mikkelsen et al
      • 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.
      investigated dispatches of a ground-based critical care team and found a 30-day mortality rate of 5.7%. Our results may indicate that for the few HEMS patients primarily triaged to a DGH but subsequently needing a secondary transfer to a university hospital, this delay does not seem to negatively influence their mortality when comparing this with the mortality of the entire HEMS patient population. Still, even these HEMS patients have considerably higher mortality rates than those reported from less selected Danish prehospital patient groups.
      • Østerås Ø
      • Brattebø G
      • Heltne JK
      Helicopter-based emergency medical services for a sparsely populated region: a study of 42,500 dispatches.
      ,
      • Christensen EF
      • Larsen TM
      • Jensen FB
      • et al.
      Diagnosis and mortality in prehospital emergency patients transported to hospital: a population-based and registry-based cohort study.
      We found a higher proportion of secondary transfers in the HEMS-assisted group (1.4%) than in the HEMS-escorted group (0.4%). Furthermore, the majority of the HEMS-assisted patients were assigned an NACA score of 3 or below, indicating a non–life-threatening condition. We noticed that the most frequent causes of a secondary transfer among these patients were an acute myocardial infarction or a traumatic lesion. In the HEMS-escorted group, patients diagnosed with a cerebral hemorrhage or an acute myocardial infarction frequently required a secondary transfer. Furthermore, a considerable number of patients in both groups were assigned a nonspecific (DZ) diagnosis in both destinations.
      Whether these secondarily transferred patients initially considered not to be in need of transfer to a university hospital direct from scene may have deteriorated into a more severe condition during transportation or within hours from arrival at the DGH are not clear. Moreover, the more refined patient evaluation available on a DGH (compared with on scene) may rely on more advanced diagnostic tools than available on scene for identifying specific traumatic injuries or cerebral lesions.

      Strengths and Limitations

      A strength of this study is the national population-based design including high data quality from a complete HEMS patient population. In addition, the Danish health care system is publicly funded and available for all Danish citizens and noncitizens, ensuring a genuine and unselected population.
      However, the study has the following limitations:
      • 1.
        The study cohort consists of a small number of patients, making it hard to draw definitive conclusions.
      • 2.
        There is a paucity in comparable national as well as international prehospital studies restricting the possibility for making comparisons with results from other HEMS systems.
      • 3.
        The registration procedure regarding the ICD-10 diagnoses might differ from one hospital to another, leading to a diagnostic inconsistency. One example could be the use of nonspecific diagnoses (DZ00-DZ99), which are frequently used in some emergency departments. Moreover, triage and patient treatment in a prehospital setting is complex and demanding, making interrater variability likely. This variability may influence the registration of data, potentially leading to bias.
      • 4.
        This study includes no information regarding the number, diagnoses, and cause of death of HEMS patients who died at a DGH. This group may include patients who died during their hospital stay from reasons not related to their prehospital triage as well as patients with critical nonsurvivable injuries/illness triaged to a DGH for palliative care and patients who died at a DGH because of being undertriaged by the HEMS physician. Analysis of these patients was beyond the scope of our study, but it seems highly unlikely that lethal undertriage should be anything but rare when undertriage resulting in a secondary transfer only occurs in 0.7% of the patients seen by HEMS.
      • 5.
        We cannot make assumptions regarding the extent of any possible overtriage (ie, patients being transported to a university hospital without actually needing the specialized care provided there).
      • 6.
        The results in this study are based on data from 1 national HEMS. Therefore, the generalizability may be limited to other prehospital critical care units with analogous staffing, dispatch criteria, case mix, and caseload.

      Perspective and Future Research

      This study is the first to describe a patient undergoing secondary transfers from a DGH to a university hospital during the first 24 hours after being treated by HEMS in a complete national HEMS patient population.
      Secondary transfer may delay crucial medical treatment for the patient, potentially leading to an increased morbidity and mortality. Therefore, an in-depth knowledge of triage systems, presumed diagnoses, and characteristics of these patients may be important for optimizing the HEMS service in the future.
      Because the number of secondary transported patients in this study is relatively low, larger studies are warranted to evaluate the reasons for these transfers. Also, studies are needed to investigate the extent of possible overtriage to university hospitals.

      Conclusion

      Patients initially triaged to a DGH by the HEMS teams seldomly required a secondary transfer to a university hospital during the first 24 hours after the initial 1-1-2 call. This indicates a low degree of prehospital undertriage for direct transfer to a university hospital. The extent of overtriage to university hospitals are unknown. Almost two thirds of the secondarily transferred patients were initially treated for either a cardiovascular or a neurologic emergency. Mortality among these patients seems comparable with that in the general population of patients treated by the Danish HEMS.

      Appendix. Supplementary materials

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