To the best of our knowledge, this study is the first to apply SI and MSI in the context of injury mechanisms resulting from traffic collisions.
Berger et al. found that SI ≥ 1.0 exhibited the highest specificity as a predictor for both 28-day mortality and hyperlactatemia in cases of sepsis presenting to the ED [13]. Dissimilar from our results, Montoya et al. found that mortality was correlated with an SI > 0.9 in patients with acute polytrauma [14]. However, their study included both penetrating and blunt injuries, which differed significantly from the injuries included in the present study. We realize that different groups of patients will have different reference values when using SI and that it is highly valuable to allow frontline healthcare providers to assess the severity of conditions and be more vigilant in caring for different patients [13, 15, 16]. Our study population was derived from traffic collisions, in which all patients had blunt injury mechanisms. Therefore, mortality outcomes correlated with an SI > 1.11 may only be particularly applicable to this population.
In this study, SI > 0.84 upon arrival in the initial level of care for individuals involved in traffic collisions serves as a predictor for the need of blood transfusion, as determined by the Youden index. A similar approach to the SI cutoff value was reported by Marenco et al. [17], wherein they investigated significant factors associated with the requirement for massive transfusion (MT) and emergency surgery in patients with trauma within the civilian population, identifying an SI cutoff point of 0.8. In a previous retrospective analysis involving 8111 civilian patients with blunt trauma admitted to a Level 1 trauma center, SI > 0.9 was correlated with a substantially elevated likelihood of requiring MT [18]. In a recent retrospective study by El-Menyar et al., which included 8710 civilian patients with trauma admitted to a Level 1 trauma center, SI > 0.8 on arrival emerged as a significant predictor for MTP, requirement for laparotomy, and in-hospital mortality [19].
Through a comprehensive review of existing studies, we defined the need for blood transfusion as administration of four units of PRBCs within 24 h. This rationale behind this definition was partly influenced by our hospital's transfusion practices, which align closely with the onset of changes in vital signs in grade II hemorrhagic shock, indicating the need for blood transfusion. In other studies, such as those by DeMuro et al., bleeding was defined as the receipt of two units of PRBCs [20]. Conversely, many studies have defined MT as administration of 10 units of PRBCs [17, 21]. We adopted an intermediate approach, setting the threshold at 4 PRBC units. With a Youden index falling between 0.8 and 0.9 and an OR over nine-fold, we can confidently assert that SI > 0.84 predicts the need for blood transfusion.
Crawford et al. reported that with each 0.1 unit rise in SI, the odds of requiring ESI increased by 21% in surgical patients. The SI was higher for blunt injuries than for penetrating injuries (0.95 vs. 0.73) [22]. Given that our patient population comprised exclusively of blunt trauma cases, our analysis aligned perfectly with the previous blunt trauma subgroup results, with the same value of 0.95. We can infer that penetrating injuries may cause more noticeable wounds, leading to a higher likelihood of surgery, even before hemodynamic changes occur. In contrast, blunt trauma may not exhibit obvious signs of bleeding or the need for surgical investigation of the open wound, prompting the need for surgery only after a certain degree of blood loss and the onset of hemodynamic changes, resulting in higher SI. We posit that employing SI at the bedside could prove invaluable in low-resource settings by providing early notification to clinicians regarding patients with initially stable vital signs but with a heightened probability of needing ESI or facing mortality.
Upon reviewing the literature related to SI and TAE, studies primarily focused on cases with known severe localized bleeding, such as in the facial area. These studies used SI to assess the severity of bleeding but did not provide any direct data for using SI as a predictive tool for the necessity of TAE [23, 24]. In contrast, our results demonstrated acceptable predictive power for using SI to determine the need for TAE. However, the use of SI and MSI for TAE prediction should be subjected to further statistical analyses and the development of more precise research methodologies.
Finally, ICU admission was correlated with SI > 0.74 in our study. In comparison, SI ≥ 0.85 was indicative of ICU admission in a retrospective analysis conducted at a single center by Keller et al. [25]. Another study demonstrated that SI ≥ 0.9 upon initial arrival at the ED served as a predictor for both in-hospital mortality and ICU admission [26]. However, the study population included general patients in the ED, instead of patients with trauma. Toccaceli et al. found that an SI threshold value of 1.05 demonstrated the highest predictive efficacy for ICU admission in patients with multiple traumas [27]. Comparing our own results for patients involved in traffic collisions, the SI in these previous studies vary to some extent, possibly because of the different populations or different mechanisms of injury. Additionally, the results may have been influenced by our medical strategies and the relatively high availability of ICUs.
MAP best represents the tissue perfusion status, and MSI reflects both stroke volume and systemic vascular resistance [11]. MSI serves as a crucial predictor of mortality, surpassing the individual predictive capacity of HR, SBP, and SI, with an optimal cutoff value exceeding 1.3 [28]. In contrast, a multicenter study examining data from 45,880 patients with trauma across 20 EDs reported no discernible differences in the predictive capacity of SI and MSI for in-hospital mortality [29]. Herein, we aimed to investigate whether MSI was more accurate than SI in its predictive value and found that MSI did not exhibit superior discriminatory ability compared to SI in predicting outcomes, such as mortality, blood transfusion, ESI, TAE, or ICU stay in our cohort.
When managing cases involving traffic collisions, patients who are admitted to the ED are in a race against time to receive treatment. At our Level I trauma center, we noted a recurring occurrence wherein patients often experienced a substantial delay in receiving treatment, even after undergoing comprehensive evaluation and completing all requisite imaging and diagnostic procedures. In this context, SI and MSI are uncomplicated scoring systems suitable for bedside applications that can provide quick and reliable treatment decision-making to expedite this process.
This study had some limitations. First, because of the retrospective study design, there was a potential for selection bias, and our sample population, compared with that of various international studies [17–19, 22], was relatively small. Second, our hospital did not implement an MTP, instead relying on routine methods, such as transfusion guidelines. Therefore, the criteria for transfusion in our study were relatively lenient compared to those requiring MTP activation. Finally, we did not strictly define the type of surgery used; therefore, some surgeries that were not life-related may have been included in the data analysis, resulting in inaccurate results. In the future, as the dataset becomes more extensive, it will be feasible to categorize the surgical procedures into distinct types. Our data appear to be significant for a Taiwanese population and allows us to draw conclusions that apply to our local situation.