Trauma Survival Margin Analysis: A Dissection of Trauma Center Performance through Initial Lactate

Abstract

Measurement of trauma center performance presently relies on W-score calculation and comparison to national data sets. A limitation to this practice is a skewing of the W score, as it determines overall performance of a trauma population that is often heavily weighted by patients of low acuity. The University of Virginia relative mortality metric (RMM) was formulated to provide higher resolution in identifying areas of performance improvement within subpopulations of a trauma center using traditional Trauma Injury Severity Score methodology. Lactic acidosis has been established as a risk factor for mortality in the setting of trauma. This study aims to compare survival margin, defined as the area between actual and predicted mortality curves, in patients with either normal or elevated initial lactate. W score and RMM were calculated and compared in these cohorts. Whereas the W score suggested increased survival within the high initial lactate group, the RMM demonstrated the expected finding of increased survival margin in the normal lactate cohort. The RMM is a potentially valuable tool for trauma centers to monitor and improve performance. In addition, these findings validate the use of lactate as a triage and risk adjustment tool in the trauma setting.

The Evolution of Trauma Care: Relative Mortality Analysis at a Level 1 Trauma Center over Two Decades

“…One of the issues with the W-score is that it fails to distinguish between patients of differing probabilities of survival (POS), thus the outcomes in using such a metric may be skewed. 4 This poses a problem with most trauma centers because they are traditionally dominated by patients with a high POS (POS > 0.94). 4,5 At some trauma centers, an increase in mortality has been seen because of the increase in higher acuity patients.…”

“…4 This poses a problem with most trauma centers because they are traditionally dominated by patients with a high POS (POS > 0.94). 4,5 At some trauma centers, an increase in mortality has been seen because of the increase in higher acuity patients. 6 This stresses an even greater need for a way to account for potentially skewed data.…”

“…The relative mortality metric (RMM) was developed at the University of Virginia and compares actual and expected survivors across an equally represented spectrum of patients. 4 Patients are compared by subpopulation with similar anticipated mortality. Previous studies using the RMM have demonstrated that it may be superior to the W-score in certain settings, such as initial lactate on mortality.…”

“…Previous studies using the RMM have demonstrated that it may be superior to the W-score in certain settings, such as initial lactate on mortality. 4 One disadvantage of the metric is that it requires large, diverse populations for analysis with a large percentage of severely injured patients because there must be sufficient patients in each POS bin to have reliable results.…”

“…Developed at our institution, the RMM and its specifics can be found in Kassar et al 4 It uses nonlinear binning and optimally subdivides patients by their POS, allowing maximal resolution and statistical confidence. The RMM produces both a numerical and graphical visualization of data.…”