Global changes in mortality rates in polytrauma patients admitted to the ICU—a systematic review

A systematic review of all published literature according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was conducted [7]. We aimed to identify all studies that reported on mortality in polytrauma patients (injury severity score (ISS) > 15) admitted to the ICU. On the 26th of February 2020, we systematically searched the PubMed, Cochrane library, and Embase databases. The search terms “polytrauma”, “ICU”, and “mortality” plus their plural forms and synonyms were used. The complete search strings are provided in Appendix 1. Duplicates were removed using an online screening program (Rayyan [8]), and all remaining articles were independently screened by JvB and MN based on the title and abstract. Potentially relevant papers were selected, and full texts were obtained. When correspondence details of the authors were available, they were contacted in case the full text could not be obtained online or from our university library. Articles were excluded when no full text was available; when title, abstract, or full text was not in English, German, French, Spanish, or Dutch; when only a specific subset of trauma patients was researched, e.g., solely severe thoracic trauma; when all included patients suffered from a specific condition e.g., sepsis; and when it concerned reviews or conference abstracts. The references of included papers were screened using the same criteria, as well as the references of relevant and related reviews.

Elements from the Critical Appraisal Skills Programme (CAPS), the Methodological Index for Non-Randomized Studies instrument (MINORS), and the Risk of Bias in Non-Randomized Studies of Interventions (ROBINS-I) tool were used to assess the methodological quality of eligible articles [9‐11]. Elements included in this assessment comprised clarity and relevance of the study aim, study design, and different types of bias, e.g., selection, detection, and reporting bias. An example of selection bias is when patients were not consecutively included. An example of reporting bias is when the authors did not describe clearly how the cause of death was determined. Suppressing or revealing information selectively is an example of reporting bias. Similar to the MINORS instrument, a score of 0, 1, or 2 points was awarded for each criterion: 0 points were assigned when an item was not reported, 1 point when an item was reported but inadequately, and 2 points when an item was adequately reported, leading to a maximum of 12 points per study.

Data on all-cause mortality, cause-specific mortality, mechanism of injury, and geographical location were extracted from the included articles. The end of data collection from each included study was used (instead of the year of publication) for all analyses to place the data in the right time frame. Cause-specific mortality was stratified in brain injury, thoracic injury, abdominal injury, death by exsanguination, multiple organ dysfunction syndrome (MODS, definitions used by the included articles are shown in Table 1), acute respiratory distress syndrome (ARDS, Table 1), sepsis (Table 1), and death from a cardiac cause. Other causes were categorized as “miscellaneous”. Mechanism of injury was stratified in blunt and penetrating trauma. A second, more detailed analysis for trauma mechanism was performed by using the following categories: traffic accidents, falls from height, workplace accidents, suicide, assault, penetrating injury, and miscellaneous.

Trends in all-cause mortality and cause-specific mortality over time were visualized and analyzed using Poisson regression models (R Core Team (2015). R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://​www.​R-project.​org/​). A p value < 0.05 was considered statistically significant.

The initial search identified 2704 articles (Fig. 1). One additional article was obtained through personal knowledge of one of the authors. We excluded 429 duplicates after which 2276 articles remained. These were screened by JvB and MN based on their title and abstract. Full texts were then obtained whenever possible. In total, 30 articles were found eligible for this review [12‐32]. All references and citations from these 30 articles were screened and identified in Web of Science. However, this did not result in additional relevant articles.

An overview of the study characteristics is provided in Table 2. Thirty studies published between 1985 and 2018 were included in this review with a total of 82,272 patients. Inclusion criteria varied per study and ranged from multiple criteria, such as a minimum ISS or age, to no additional criteria apart from “polytrauma patients” and “admission to the ICU.” Also, the number of included patients varied widely from 20 to 31,154 patients, as well as the study duration with a minimum of 1.5–2 years in the study of Dereeper et al. [15] and a maximum of 30 years for the study of Probst et al. [28]. Most studies were carried out in Europe, and especially Germany was well represented ([12‐14, 17, 28, 29, 31, 33‐37] 12 out of 19 European studies [12‐17, 22, 23, 25, 26, 28, 29, 31‐36, 38] were German). Four studies took place in Asia [18, 20, 21, 37], three in the USA [19, 27, 39], two in South America [40, 41], and two in Australia [24, 30].

An overview of the quality of the included studies is given in Table 3. All studies apart from one [21] clearly described their study design. Most studies were retrospective, although data was sometimes collected prospectively in a trauma registry. There was no indication for selection bias in all 30 studies except for three [33, 34, 37]. Either patients were not consecutively included or the inclusion process was not clearly described in these articles. Five studies did not clearly describe how they obtained data on the cause of death [12, 13, 20, 21, 25]. Eleven studies scored the maximum number of points [19, 22, 23, 27, 29‐32, 41‐43]. The lowest score was five points [37].

All 30 papers reported all-cause mortality rates in their study population (Table 1). Seven studies stratified their total study duration in smaller time spans and reported mortality rates for each time span [13, 17, 22, 25, 28, 29, 31]. All available information was included in our analysis of all-cause mortality.

All-cause mortality rates in polytrauma patients admitted to the ICU was observed to decrease over time (Fig. 2). We note that there was substantial variation between studies. For example, the study by Mazandarani et al. [37] showed a relatively high mortality (31%) considering its time period (2012), whereas Goins et al. reported a relatively low mortality (6%) for its time period (1988) [27]. Mortality decreased with approximately 1.8% per year (95% confidence interval (CI) 1.6–2.0%, p < 0.001).

Fifteen of the included articles reported data on the individual causes of death [12‐17, 19‐23, 32, 34, 36, 41]. One paper provided date from five independent time periods leading to a total of 19 data points [17]. Multiple organ dysfunction syndrome (MODS) was reported as the main cause of death in several studies until the end of the last century [13, 14, 17]. At the turn of the century, this altered and brain injury often became the leading cause of death. Figure 3 shows the relative contributions (cause-specific mortality as a percentage of all ICU mortality in trauma patients admitted to the ICU). The relative contribution to ICU mortality of MODS, ARDS, and sepsis decreased over time: relative decreases per year of 1.9% (95% CI 1.2–2.7%), 8.4% (95% CI 6.0–10.6%), and 1.7% (95% CI 0.5–2.9%), respectively. In conjunction with this decrease, an increase was observed for the relative contribution to ICU mortality of brain injury and hemorrhage: relative increases per year of 2.5% (95% CI 1.9–3.0%) and 1.9% (95% CI 1.0–2.9%), respectively.

Thirteen of the 30 included articles provided data on mechanism of injury sustained by their study population [12, 14‐16, 20‐22, 26, 27, 36, 37, 39, 40]. There have been no changes in the ratio of blunt and penetrating trauma over time (Fig. 4a). Traffic accidents were the most prevalent trauma mechanism reported in all articles, although there has been a decrease of approximately 25% in almost 25 years (Fig. 4b). Falls and workplace accidents were often reported as the second most common trauma mechanism. Assault, suicide attempts, accidental injuries, and penetrating injuries (stab wounds as well as gunshot wounds) were all less common causes of trauma, but were similarly prevalent throughout all years.

The included articles were divided into subgroups representing the continent of the study population. First, differences in all-cause mortality between continents were analyzed for studies published after 2000 to reduce temporal influences (Table 1, Europe n = 17, South America n = 2, North America n = 2, Asia n = 3) (Fig. 4). Weighted averages based on the study population of each study resulted in 14.4% all-cause mortality for Europe, 22.6% for South America, 9.6% for North America, and 18.5% for Asia. Further analyses on geographical differences, such as blunt/penetrating trauma and the most prevalent cause of death, can be found in Appendix 2.