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

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.

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).

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).

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.