How to define severely injured patients?—An Injury Severity Score (ISS) based approach alone is not sufficient

  • Thomas Paffrath
    Correspondence
    Corresponding author at: Department of Orthopaedic and Trauma Surgery, University of Witten/Herdecke, Cologne-Merheim Medical Center (CMMC), Ostmerheimer Str. 200, D-51109 Cologne, Germany. Tel.: +49 221 89 07 13 116; fax: +49 221 89 07 35 80.
    Affiliations
    Department of Orthopaedic and Trauma Surgery, University Witten/Herdecke, Cologne-Merheim Medical Center (CMMC), Cologne, Germany

    Committee on Emergency Medicine, Intensive Care and Trauma Management (Sektion NIS) of the German Trauma Society (DGU), Germany
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  • Rolf Lefering
    Affiliations
    Institute for Research in Operative Medicine (IFOM), University Witten/Herdecke, Cologne, Germany
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  • Sascha Flohé
    Affiliations
    Department of Trauma and Hand Surgery, University Hospital Duesseldorf, Duesseldorf, Germany

    Committee on Emergency Medicine, Intensive Care and Trauma Management (Sektion NIS) of the German Trauma Society (DGU), Germany
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  • Affiliations
    Committee on Emergency Medicine, Intensive Care and Trauma Management (Sektion NIS) of the German Trauma Society (DGU), Germany

      Abstract

      Introduction

      Multiple injured patients, polytrauma or severely injured patients are terms used as synonyms in international literature describing injured patients with a high risk of mortality and cost consuming therapeutic demands. In order to advance the definition of these terms, we analysed a large trauma registry. In detail, we compared critically ill trauma patients first specified on a pure anatomical base according to the ISS or NISS, second in the original “polytrauma definition” with two body regions affected and finally all of them combined with a physiological component.

      Patients and methods

      Records that were collected in the TraumaRegister DGU® of the German Trauma Society (Deutsche Gesellschaft für Unfallchirurgie, DGU) between 1993 and 2011 (92,479 patients) were considered for this study. All patients with primary admission from scene with a minimum hospital stay of 48 h and an Injury Severity Score (ISS) ≥ 16 were included. Pre-hospital and early admission data were used to determine physiological risk factors and calculate individual risk of death using the Revised Injury Severity Classification (RISC).

      Results

      45,350 patients met inclusion criteria. The overall hospital mortality rate was 20.4%. The predicted mortality according to the RISC-Score was 21.6%. 36,897 patients (81.4%) had injuries in several body regions. The prevalence of the five physiological risk factors varied between 17% (high age) and 34% (unconsciousness). There were 17,617 patients (38.8%) without any risk factor present on admission, while 30.6% (n = 13,890) of the patients had one and 30.5% (n = 13,843) had two or more factors present. Patients with ISS ≥ 16 but no physiological risk factor present had a very low mortality rate of 3.1% (542 of 17,617). With an increasing number of physiological factors there was an almost linear increase in mortality up to an 86% rate in patients with all five factors present. The ‘polytrauma’ definition of Butcher and colleagues with AIS ≥ 3 in at least two different body regions would apply to only 56.2% of patients in the present group with ISS ≥ 16. The mortality in this subgroup is only marginally higher (21.8%; 5559 of 25,494) than in the group of patients with only one severely affected body region (18.5%; 3675 of 19,875).

      Conclusions

      In our opinion the principle of sharpening an anatomically based definition by a defined physiological problem will help to specify the really critically ill trauma patients.

      Keywords

      Introduction

      Multiple injured patients, polytrauma or severely injured patients are terms used as synonyms in international literature describing injured patients with a high risk of mortality and cost consuming therapeutic demands. Since the early 1970s scoring systems have been used to describe the above-mentioned patients. The most frequently trauma score used is the Injury Severity Score (ISS), first published by Baker et al. [
      • Baker S.P.
      • O’Neill B.
      The injury severity score: an update.
      ]. The ISS describes injury severity purely on the basis of anatomical findings defined in the Abbreviated Injury Scale (AIS). The AIS in its most recent version (version 2005, update 2008) lists about 2000 different injuries in nine body regions. The severity of each individual injury is graded on a scale from 1 to 6 points where 1 point describes minor injuries, and 6 points are given for untreatable, mostly lethal injuries. In order to calculate the ISS, each AIS score is assigned to one out of six different body regions. The ISS is calculated as the sum of the squares of the highest AIS code in each of the three most severely affected body regions [
      • Lossius H.M.
      • Rehn M.
      • Tjosevik K.E.
      • Eken T.
      Calculating trauma triage precision: effects of different definitions of major trauma.
      ]. In most clinical studies the cohort of critically ill trauma patients is defined by ISS ≥ 16 points found in the Major Trauma Outcome Study (MTOS) associated with a mortality risk of 10% [
      • Champion H.R.
      • Copes W.S.
      • Sacco W.J.
      • Lawnick M.M.
      • Keast S.L.
      • Bain Jr., L.W.
      • et al.
      The Major Trauma Outcome Study: establishing national norms for trauma care.
      ].
      Recently, trauma centres demand a defined caseload not only in the United States but also in some European countries [
      • Deutsche Gesellschaft für Unfallchirurgie
      Weißbuch Schwerverletztenversorgung.
      ]. The American College of Surgeons Committee on Trauma (ACS COT) requires a minimum of 1200 annual trauma admissions at each of the 110 American College of Surgeons (ACS) verified Level I facilities in the United States. Of these, 20% (240 patients) should have an Injury Severity Score (ISS) of at least 16 points. In this context the ISS ≥ 16 definition serves as an injury severity measure for caseload requirements.
      Because of several well-known problems in calculating mortality based on ISS the New Injury Severity Score (NISS) modified the calculation by using the three most severe injuries regardless of body region [
      • Osler T.
      • Baker S.P.
      • Long W.
      A modification of the injury severity score that both improves accuracy and simplifies scoring.
      ]. Based on this modification the prognostic value of predicting survival rate could be improved especially for penetrating trauma and isolated head injury [
      • Lavoie A.
      • Moore L.
      • LeSage N.
      • Liberman M.
      • Sampalis J.S.
      The New Injury Severity Score: a more accurate predictor of in-hospital mortality than the Injury Severity Score.
      ,
      • Tay S.-Y.
      • Sloan E.P.
      • Zun L.
      • Zaret P.
      Comparison of the New Injury Severity Score and the Injury Severity Score.
      ]. Based on these findings an NISS ≥ 16 is recommended in the Utstein template [
      • Ringdal K.G.
      • Coats T.J.
      • Lefering R.
      • Di Bartolomeo S.
      • Steen P.A.
      • Røise O.
      • et al.
      The Utstein template for uniform reporting of data following major trauma: a joint revision by SCANTEM, TARN, DGU-TR and RITG.
      ] as inclusion criteria for major trauma.
      Alternatively a variety of additional approaches exist to define the severity of trauma patients especially in central Europe. The term “Polytrauma” was coined by Tscherne et al. [
      • Tscherne H.
      • Oestern H.J.
      • Sturm J.A.
      Stress tolerance of patients with multiple injuries and its significance for operative care.
      ] as “Multiple injuries, of which one, or their combination, is life threatening”. The frequently used term “severely injured patients” with a threshold of ISS ≥ 16, however, does not necessarily demand the presence of more than one injury. An isolated AIS grade 4 or 5 injury would fulfil this definition as well. Such an inconsistent description of trauma patients is a problem: e.g. for inclusion criteria in clinical studies, epidemiological evaluation of trauma databases, minimal caseload definition for trauma centres or economical calculation. The idea behind the existing definitions is to identify trauma patients with high risk of mortality. But is anatomical injury severity sufficient for this purpose? Different studies have pointed out the limited prognostic value of anatomical scores alone, such as the ISS and NISS, in terms of mortality prediction [
      • Haider A.H.
      • Villegas C.V.
      • Saleem T.
      • Efron D.T.
      • Stevens K.A.
      • Oyetunji T.A.
      • et al.
      Should the IDC-9 Trauma Mortality Prediction Model become the new paradigm for benchmarking trauma outcomes?.
      ,
      • Tohira H.
      • Jacobs I.
      • Mountain D.
      • Gibson N.
      • Yeo A.
      Systematic review of predictive performance of injury severity scoring tools.
      ]. Therefore, more sophisticated prognostic scores, such as the Revised Injury Severity Classification (RISC-Score) [
      • Lefering R.
      Development and validation of the revised injury severity classification score for severely injured patients.
      ] or the TRISS method [
      • Boyd C.R.
      • Tolson M.A.
      • Copes W.S.
      Evaluating trauma care: the TRISS method. Trauma Score and the Injury Severity Score.
      ] added physiological risk factors (e.g. unconsciousness, shock, or acidosis) and age in order to increase the prognostic value. In the light of this finding, it sounds logical to include such parameters into a definition of “severely injured patients” in order to meet the above-mentioned demands.
      Several groups suggested that at least two anatomical regions had to be injured to be defined a critically ill trauma patient. Their intention was to define the term “polytrauma” – a term used especially in central Europe. The term does not really exist in the English language but there is a considerable amount of literature using the term “polytrauma” or “polytraumatized”. Actually, it is more or less a linguistic discussion whether the prefix “poly” with an ancient Greece origin should be translated with “many” in the sense of “several injuries” or “much” in the context of life threateningly injured. This is also reflected in the different explanations of the term “polytrauma” in textbooks: e.g. some authors specify the word “polytrauma” according to the presence of two or more body regions injured [
      • Oestern H.J.
      • Dürig M.
      Polytrauma.
      ,
      • Tscherne H.
      • Regel G.
      • Sturm J.A.
      • Friedl H.P.
      Degree of severity and priorities in multiple injuries.
      ]; others include into their definition an ISS ≥ 16 points as a potential life threat; others again add the systemic reaction with dysfunction of primarily undamaged organ systems to their definition [
      • Wanner G.A.
      • Trentz O.
      Klinische Akutversorgung des Polytraumatisierten.
      ]. Butcher et al. intended to sharpen the definition of the term. Therefore, they used trauma registry data to define “polytrauma” as an injured patient with AIS ≥ 3 points in at least two different body regions [
      • Butcher N.
      • Balogh Z.J.
      AIS > 2 in at least two body regions: a potential new anatomical definition of polytrauma.
      ]. This definition corresponds to ISS ≥ 18 but still excludes an isolated grade 5 injury or multiple injuries of the same body region. It remains debatable, whether the principle demand of more than one body region to be injured is actually helpful to define trauma patients with high mortality as well as to predict the requirement of therapeutic care and resources. An international consensus meeting in 2012 first tried to specify the term “polytrauma” by combining the concept of injuries in different body regions and physiological risk factors [
      • Pape H.-C.
      Classification of patients with multiple injuries – is the polytrauma patient defined adequately in 2012?.
      ,
      • Pape H.-C.
      • Lefering R.
      Grading of injury severity – What should be the prerequisites to separate multiply injured patients from those in critical condition and polytrauma?.
      ].
      Osler et al. [
      • Osler T.
      • Baker S.P.
      • Long W.
      A modification of the injury severity score that both improves accuracy and simplifies scoring.
      ] introduced a different approach when they published the New ISS (NISS) as it considered multiple injuries within the same body region. As this approach was more precise in predicting mortality the European recommendation for documentation advises the NISS ≥ 16 as an inclusion criteria for trauma registries.
      In order to advance the definition of the term, we analysed a large trauma registry with the purpose of classifying critically ill trauma patients with a high risk of mortality. In detail, we compared critically ill trauma patients first specified on a pure anatomical base according to the ISS or NISS, second in the original “polytrauma definition” with two body regions affected and finally all of them combined with a physiological component.

      Patients and methods

       The TraumaRegister DGU®

      The TraumaRegister DGU® was founded in 1993. The aim of this multi-centre database is an anonymous and standardised documentation of severely injured patients. Data are collected prospectively in four consecutive time phases from the site of the accident until discharge from hospital: (A) pre-hospital phase, (B) emergency room and initial surgery, (C) intensive care unit and (D) discharge. The documentation includes detailed information on demographics, injury patterns, comorbidities, pre- and in-hospital management, course on intensive care unit, relevant laboratory findings including data on transfusion and outcome of each individual. The inclusion criteria are admission to hospital via emergency room with subsequent ICU/ICM care or arrival at the hospital with vital signs but death before admission to ICU.
      The infrastructure for documentation, data management, and data analysis is provided by AUC – Academy for Trauma Surgery (AUC – Akademie der Unfallchirurgie GmbH), a company affiliated to the German Trauma Society. The scientific leadership is provided by the Committee on Emergency Medicine, Intensive Care and Trauma Management (Sektion NIS) of the German Trauma Society. The participating hospitals submit their data anonymously into a central database via a web-based application. Scientific data analysis is approved according to a peer review procedure established by Sektion NIS.
      The participating hospitals are primarily located in Germany (90%), but a rising number of hospitals of other countries contribute data as well (at the moment hospitals from Austria, Belgium, China, Finland, Luxembourg, Slovenia, Switzerland, The Netherlands, and the United Arab Emirates). Currently, approximately 25,000 cases from more than 600 hospitals are entered into the database per year. The participating in TraumaRegister DGU® (data set of approximately 100 entries) is voluntary. Nevertheless for hospitals associated with TraumaNetzwerk DGU® a basic data set (reduced QM data set of approximately 40 entries) is obligatory for reasons of quality assurance. Records that were collected between 1993 and 2011 (92,479 patients) were considered for this study. Patients for this study were selected according to the following criteria:
      • Primary admission to the hospital (no transfers in).
      • No transfers out within 48 h.
      • Injury Severity Score (ISS) ≥ 16.
      Patients transferred in were excluded due to missing pre-hospital data, and patients transferred out early were excluded since final outcome was not available. Pre-hospital and early admission data were used to determine physiological risk factors and calculate individual risk of death using the Revised Injury Severity Classification (RISC) [
      • Lefering R.
      Development and validation of the revised injury severity classification score for severely injured patients.
      ]. A total 45,350 patients fulfilled the above-mentioned criteria and were included for further analysis.

       Data analysis

      Patients were divided in subgroups according to the number of injured body regions and the number of physiological risk factors present. The body regions are identical to those used for the ISS score. A body region was considered injured if there was at least an injury of AIS severity grade 2 (or higher). Physiological risk factors were those that are known to increase the risk of death substantially. Table 1 describes the five factors considered in this analysis. The decision of being categorised as a risk factor or not is guided by doubling the mortality rate. Only measurements available from the pre-hospital or the early admission phase were considered for these factors. Prognostic relevant events occurring later in the course of treatment, e.g. multiple organ failure or sepsis, were disregarded here. The overall number of risk factors present on admission (range 0–5) was calculated by simply adding the individual findings. In case that a certain risk factor was not available due to missing values, this factor was assumed not to be present.
      Table 1Definition of risk factors.
      Risk factorDefinition
      High age≥70 years
      AcidosisBase excess < −6
      UnconsciousnessGCS 3–8 (pre-hospital)
      HypotensionSystolic blood pressure ≤ 90 mm Hg (pre-hospital or on admission)
      CoagulopathyAt least one of the following:

      Quick's value < 60% or

      Partial thromboplastin time (PTT) ≥ 40 s or

      INR ≥ 1.4

       Statistical analysis

      Data were analysed with the Statistical Package for the Social Sciences (SPSS; version 22, IBM Inc., Armonk, NY, USA). Incidences are represented as the number of cases and percentages, and measured values are represented as means and standard deviations. The present study is in line with the publication guideline of the TraumaRegister DGU® and registered as TR-DGU project ID 2012-044.

      Results

      The overall hospital mortality rate in patients with ISS ≥ 16 was 20.4%. In 90.4% of cases (n = 40,979) the predicted mortality according to the RISC-Score was 21.6%, compared to the observed mortality rate of 20.0%. The majority of patients (n = 36,897, 81.4%) had injuries in several body regions (Table 2). The group of patients with only one injured body region (referred to as “monotrauma”) may still have multiple injuries, however, all in the same body region. Injuries of five (2.9%) or six (0.2%) body regions are very rare.
      Table 2Descriptive data of patients with one and more than one body region affected.
      Risk factorOne body regionTwo or more body regions
      Number of cases8454 (18.4%)36,896 (81.4%)
      Age (mean, SD)51.3 (23.2)44.0 (20.6)
      Male sex (%)70.6%73.1%
      Penetrating trauma (%)7.6%3.3%
      ISS (mean, SD)22.8 (11.5)30.1 (12.2)
      Head injury (AIS ≥ 3)68.7%52.7%
      Chest injury (AIS ≥ 3)16.7%67.0%
      Abdominal injury (AIS ≥ 3)5.6%23.8%
      Injury of extremities (AIS ≥ 3)8.1%42.7%
      No risk factor present (%)36.8%39.3%
      Hospital mortality30.1%18.1%
      The definition of the five physiological risk factors is given in Table 1. The corresponding mortality rates when the risk factor is present or not are given in Table 3. The prevalence of the five risk factors varied between 17% (high age) and 34% (unconsciousness). There were 17,617 patients (38.8%) without any risk factor present on admission, while 30.6% (n = 13,890) of the patients had one and 30.5% (n = 13,843) had two or more factors present. Table 4 provides descriptive data of these subgroups.
      Table 3Hospital mortality rate with and without the presence of physiological risk factors.
      Risk factorMortality if not presentMortality if presentPrevalence
      High age16.2%40.6%17.0%
      Acidosis14.3%40.6%22.4%
      Unconsciousness8.9%42.9%34.2%
      Hypotension13.9%37,4%28.2%
      Coagulopathy11.6%40,2%24.3%
      Table 4Descriptive data of patients with none, one, or more than one risk factor present on admission.
      Risk factorNo risk factor presentOne risk factor presentTwo or more risk factors present
      Number of cases17,617 (38.8%)13,890 (30.6%)13,843 (30.5%)
      Age (mean, SD)40.1 (16.0)47.9 (22.7)49.5 (24.1)
      Male sex (%)77.5%70.9%68.2%
      Penetrating trauma (%)3.6%3.8%5.0%
      ISS (mean, SD)24.2 (8.1)27.8 (10.8)35.5 (15.2)
      Head injury (AIS ≥ 3)41.1%60.5%69.3%
      Chest injury (AIS ≥ 3)58.2%54.4%60.1%
      Abdominal injury (AIS ≥ 3)18.8%16.8%26.0%
      Injury of extremities (AIS ≥ 3)35.4%33.2%40.3%
      Only one body region affected (%)17.6%19.918.6%
      Hospital mortality3.1%16.0%46.7%
      Patients with ISS ≥ 16 but no physiological risk factor present had a very low mortality rate of 3.1% (542 of 17,617). Fig. 1 shows mortality rates for subgroups according to the number of body regions affected and the presence or absence of physiological risk factors on admission. With an increasing number of physiological factors there was an almost linear increase in mortality, as shown in Fig. 2. Patients with all five physiological risk factors present on admission had a mortality rate of 86%. An AIS ≥ 2 points in two different body regions and an overall ISS ≥ 16 is considered as “polytrauma”. Mortality increased with the number of physiological risk factors in the same almost linear way in the subgroup “polytrauma – two body regions” as well as in the remaining group “monotrauma” (Fig. 3).
      Figure thumbnail gr1
      Fig. 1Subgroups according to the number of body regions affected (one versus two or more) and the presence of physiological risk factors on admission (none versus one or more). The total number of patients with ISS ≥ 16 is 45.350.
      Figure thumbnail gr2
      Fig. 2Influence of number of risk factors present on hospital mortality in all patients with ISS ≥ 16.
      Figure thumbnail gr3
      Fig. 3Influence of number of risk factors present on hospital mortality in patients with one (‘monotrauma’) ore more than one ‘polytrauma’) body regions affected.
      The ‘polytrauma’ definition of Butcher et al. [
      • Butcher N.
      • Balogh Z.J.
      AIS > 2 in at least two body regions: a potential new anatomical definition of polytrauma.
      ] with AIS ≥ 3 in at least two different body regions would apply to only 56.2% of patients in the present group with ISS ≥ 16. The mortality in this subgroup is only marginally higher (21.8%; 5559 of 25,494) than in the group of patients with only one severely affected body region (18.5%; 3675 of 19,875).

      Discussion

      Multiple trauma patients are a very heterogeneous patient group. For numerous reasons, a further specification of these patients is desirable. Several groups suggested to include the presence of at least two injured anatomical regions in the definition of the critically ill trauma patients according to the original sense of the use of the term “polytrauma” as it was introduced by Tscherne et al. As suggested before we assumed a severe injury beginning at an AIS ≥ 2 points. From the whole group of all trauma patients with an ISS ≥ 16 points, 81% (n = 36,896) fulfilled the specification of two ISS regions injured with more than 2 AIS points. Interestingly, the mortality rate of this subgroup (“polytrauma – two body regions”) was even lower (18.7%) than in the whole group with an ISS ≥ 16 points (20.4%). Nonetheless, the fact that the subgroup “polytrauma – two body regions” had a lower overall mortality than the whole group drew the attention to the remaining subgroup that consists predominantly of isolated severe injuries of one body region and is further referred to as “monotrauma”. This group made almost 19% of all ISS ≥ 16 patients in this data analysis. It consists of an AIS 4 or 5 points injury of one body region and no additional or only minor (1 or 2 points) injury of a second ISS region. Interestingly enough, exactly this “neglected” group has the highest mortality rate and the highest RISC-Score of all groups (31% mortality rate and predicted rate of 28.9%). Regardless of this high mortality rate, the further specification of very critical patients by adding the “physiological risk factors” shows a good correlation between mortality and the present number of “physiological risk factors” (Fig. 3).
      There is a certain concern in some regions that the “monotrauma” group consists of predominantly isolated severe blunt brain injuries, which have some difference from other trauma patients both in terms of resources and prognosis. Indeed more than two third (68.7%) of the patients in the “monotrauma” group have an AIS brain > 3 points. However, severe blunt brain injury in multiple trauma is so common that in the whole group with ISS ≥ 16 the frequency of severe head injuries (AIS brain > 3) is also present in more than half of the patients (52.7%).
      The specification of a severely injured patient on a purely anatomical background includes a major amount of patients who are not at major risk to die. Therefore, we described severe trauma patients with different physiological risk factors as an attempt to further specify the severely injured patient in addition to a pure anatomical description. In fact, most of these risk factors are part of predictive scores such as the RISC-Score. The presented data line out that the possibility to specify severely injured patients by characteristics exists in addition to a pure anatomic description. If all risk factor are missing, the mortality of trauma patients with an ISS ≥ 16 is only at 3.1%.
      Three main questions can be discussed in this context. First, can severely injured patients be summed up in a single definition? Second, why should severely injured patients be specified in a more detailed manner in addition to already existing pure anatomical descriptions? And finally, what are the possibilities to accomplish this?
      Trauma indeed can affect all body regions and all organs in an endless amount of combinations. Regardless of this variety, there seems to be a typical response to multiple trauma irrespective of the location. Multiple trauma causes a global immune response that can be observed clinically as systemic inflammatory response syndrome (SIRS) [
      • Malone D.L.
      • Kuhls D.
      • Napolitano L.M.
      • McCarter R.
      • Scalea T.
      Back to basics: validation of the admission systemic inflammatory response syndrome score in predicting outcome in trauma.
      ]. The degree of inflammatory response correlates with the anatomical severity of the injury [
      • Ertel W.
      • Keel M.
      • Marty D.
      • Hoop R.
      • Safret A.
      • Stocker R.
      • et al.
      Significance of systemic inflammation in 1,278 trauma patients.
      ,
      • Napolitano L.M.
      • Ferrer T.
      • McCarter R.J.
      • Scalea T.M.
      Systemic inflammatory response syndrome score at admission independently predicts mortality and length of stay in trauma patients.
      ,
      • Sakamoto Y.
      • Mashiko K.
      • Matsumoto H.
      • Hara Y.
      • Kutsukata N.
      • Yokota H.
      Systemic inflammatory response syndrome score at admission predicts injury severity, organ damage and serum neutrophil elastase production in trauma patients.
      ]. Considering this, some authors included the SIRS in a further specification of multiple trauma patients [
      • Butcher N.E.
      • Balogh Z.J.
      The practicality of including the systemic inflammatory response syndrome in the definition of polytrauma: experience of a level one trauma centre.
      ]. However, the degree of SIRS after trauma cannot be determined on admission of the patient. In contrast, our suggested physiological risk factors have been shown to be precise predictors for mortality and are already available within the first hour.
      There are a variety of perspectives in the field of defining a severely injured patient. In Germany, official police reports specify that the severely injured patient stays over 24 h in hospital after trauma. Such a definition certainly does not meet any medical demands. As inclusion criteria for all kind of clinical or experimental trials, the characterisation of severely injured patients by anatomical description of the injury severity (ISS ≥ 16) is frequently applied. However, the purely anatomical description has a clear disadvantage. As we pointed out in the present investigation more than one third of these patients (ISS ≥ 16) have no serious deteriorations of any vital signs on admission to the hospital and reveal a very low mortality rate but are considered severely injured patients. Especially in interventional trials, which only use an anatomical specification of “severely injured”, these patients will act as confounders. It can also be assumed that the anatomical description of trauma severity does not only depend on the accidental impact itself but may also be influenced by the diagnostic algorithm. The very frequent application of whole body multislice CT-scan gives a complete overview of all injuries. Some of these injuries might not have been diagnosed a decade ago in the era of conventional radiological trauma patient work-up [
      • Salim A.
      • Sangthong B.
      • Martin M.
      • Brown C.
      • Plurad D.
      • Demetriades D.
      Whole body imaging in blunt multisystem trauma patients without obvious signs of injury: results of a prospective study.
      ]. This is especially true for pulmonary contusions, which are specified as grade 3 injuries in case of unilateral manifestation and grade 4 in bilateral occurrence in the AIS 2005 version. Many of these injuries probably would not be diagnosed without the liberal use of a CT-scanner.
      Besides a clear definition of the “severely injured” for scientific reasons there are also organisational demands that require a reasonable specification of these patients. Severely injured patients are treated in qualified trauma centres in most countries. In many regions these centres are graded in different levels according to their infrastructural capacities and their caseload. In the United States, for example, a minimal caseload of 240 patients with ISS > 16 points is demanded by the ACS for a level 1 trauma centre. But there is no clear evidence for the determination of this precise number. Data concerning minimal caseload vary a lot [
      • Caputo L.M.
      • Salottolo K.M.
      • Slone D.S.
      • Mains C.W.
      • Bar-Or D.
      The relationship between patient volume and mortality in American trauma centres: a systematic review of the evidence.
      ].
      Several reasons to sharpen a definition of severely injured patients exist. In order to select those patients with a very high risk or with a very high demand of medical care, the anatomic description has to be extended for organisational reasons. The presence of injuries in several body regions is one way to accomplish this purpose that has been suggested by several authors [
      • Butcher N.
      • Balogh Z.J.
      AIS > 2 in at least two body regions: a potential new anatomical definition of polytrauma.
      ,
      • Butcher N.
      • Balogh Z.J.
      The definition of polytrauma: the need for international consensus.
      ]. We were able to point out that such a prerequisite for a definition neglects many critically injured patients, especially those with very severe single body region traumas. This “monotrauma” group revealed the highest mortality of all patients with ISS ≥ 16 points and thus, will be neglected, if only patients with two body regions injured are included in such a definition.
      A specified definition of severely injured patients by adding the physiological risk factors has some limitations in terms of general applicability and acceptance. The specification of a severely injured patient by adding physiological risk factors partly depends on laboratory values, for example, to demonstrate the presence of a coagulopathy. However, values like coagulation parameters or the base deficit are only available with a certain time delay and are not necessarily analysed in all settings. In addition, these parameters are not collected in all trauma registries. The international consensus-derived Utstein trauma template does not include variables of the coagulation system [
      • Ringdal K.
      • Lossius H.
      • Jones J.M.
      • Lauritsen J.M.
      • Coats T.J.
      • Palmer C.S.
      • et al.
      Collecting core data in severely injured patients using a consensus trauma template: an international multicentre study.
      ]. Therefore, for international purposes the proposed specification of severely injured patients still needs verification in other large trauma databases and some of the “physiological risk factors” may need modifications or substitution variables. In our opinion the principle of sharpening an anatomically based definition by a defined physiological problem will help to specify the really critical trauma patients.

      Conflict of interest

      Dr. Thomas Paffrath is deputy head of the Committee on Emergency Medicine, Intensive Care and Trauma Management of the German Trauma Society (Sektion NIS) where he leads the TR-DGU steering group together with Professor Rolf Lefering. The authors declare that they had no conflict of interest.

      Acknowledgements

      We greatly appreciated the constructive discussion with P. Giannoudis, A.P. Peitzmann, Z.J. Balogh, B. Bouillon, S. Ruchholtz and H.C Pape leading to the idea of this evaluation.

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