How to define severely injured patients?—An Injury Severity Score (ISS) based approach alone is not sufficient
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. [1]. 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 [13]. 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% [7].
Recently, trauma centres demand a defined caseload not only in the United States but also in some European countries [8]. 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 [17]. Based on this modification the prognostic value of predicting survival rate could be improved especially for penetrating trauma and isolated head injury [11], [25]. Based on these findings an NISS ≥ 16 is recommended in the Utstein template [21] 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. [28] 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 [10], [26]. Therefore, more sophisticated prognostic scores, such as the Revised Injury Severity Classification (RISC-Score) [12] or the TRISS method [2] 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 [16], [27]; 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 [29]. 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 [3]. 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 [19], [20].
Osler et al. [17] 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.
Section snippets
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
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%)
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
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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