Anion Gap as a Predictor of Trauma Outcomes in the Older Trauma Population: Correlations with Injury Severity and Mortality

The relationship among traumatic injury, the associated metabolic/physiologic responses, and mortality is well established. Tissue hypoperfusion and metabolic derangement may not universally correlate with initial clinical presentation. We hypothesized that anion gap (AG) could be a useful gauge of trauma-related physiologic response and mortality in older patients with relatively lower injury acuity. We retrospectively analyzed data from 711 trauma patients older than 45 years. Parameters examined included demographics, injury characteristics, laboratories, morbidity, and mortality. Univariate and survival analyses were performed using PASW 18. A step-wise correlation exists between increasing Injury Severity Score and AG. Although AG less than 8 to 15 was not associated with a significant increase in mortality, greater mortality was seen for AG greater than 16 with further stepwise increases for AGs greater than 22. Anion gap correlated moderately with serum lactate and poorly with base excess. Increasing AG also correlated with morbidity and greater incidence of intensive care admissions. The presence of any complication increased from 28.6 per cent for patients with AG 12 or less to 45.5 per cent for patients with AG 22 or greater (P < 0.04). These findings support the contention that “low acuity” trauma patients with high AGs may not appear acutely ill but may harbor significant underlying metabolic and physiologic disturbances that could contribute to morbidity and mortality. Higher AG values (i.e., greater than 16) may be associated with worse clinical outcomes.