Anión Cap as a Predictor of Trauma Outcomes in the Older Trauma Population: Correlations with Injury Severity and Mortality lOHN I. LESKOVAN, D.O.,*t CARLA F. JUSTINIANO, B.S.,t lOHN A. BACH, M.D.,tt CHARLES H. COOK, M.D.,t DAVID E. LINDSEY, M.D.,t DANIEL S. EIEERMAN, M.D.,t THOMAS I. PAPADIMOS, M.D.,t STEVEN M. STEINBERG, M.D.,+ SERGIO D. BERGESE, M.D.,t STANISLAW R A. STAWICKL M.D.,t DAVID C EVANS, M.D.t
From the *St. Vincent Mercy Medical Center, Toledo, Ohio; f Department of Surgery, Division of Trauma, Critical Care, and Burn, and the ^Department of Anesthesiology, The Ohio State University College of Medicine, Columbus, Ohio; ^Riverside Methodist Hospital, Columbus, Ohio 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 stepwise 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.
M
ORE THAN 2.8 MILLION people are hospitalized for traumatic injuries each year with attributable mortality of more than 180,000 deaths.' Significant proportions of preventable trauma mortalides are associated with hemorrhagic shock and the accompanying severe metabolic and physiologic disturbances.' Hypoperfusion and metabolic derangement seen in acute trauma do not universally correlate with initial clinical presentadon. Consequendy, estimating the degree of hypoperfusion and shock remains challenging.^ Serum markers of metabolic acidosis may be used to provide prognostic information and help guide the overall clinical treatment plan.^
In the trauma populadon, previous reports have shown that isolated measurements of serum pH, total CO2, base excess, or lactate have been used to quantify the level of shock and predict trauma outcomes and mortality."^^ However, these chnical indicators all have potendal limitadons.^^^ Data remain limited with regard to the use of anion gap (AG) and resuscitadon end points in the setting of acute trauma, although some evidence suggests that AG may be predictive of poor prognosis after trauma or metabolic stress in the aging populadon.'° Evidence condnues to be limited in this unique subset of padents with regard to correladons between clinical indicators and the actual degree of hypoperfusion. Although we do Presented at the 7th Annual Academic Surgical Congress, Las not routinely measure lactate or base deficit as a result Vegas, Nevada, February 14-16, 2012. of relatively low injury severity in older d-auma victims. Address correspondence and repdnt requests to David C. Evans, ^ Q measurements are available for most of these padents M.D., Department of Surgery, Division of Trauma, Critical Care,
and Bum, The Ohio State University College of Medicine, Suite 634, 395 West 12th Avenue, Columhus, OH 43210. E-mail: david.
[email protected].
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^^ ^ reported part of the Standard serum chemistry panel. This Study seeks to determine if admission AG predicts outcomes in the older trauma population.
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THE AMERICAN SURGEON
Methods and Materials
Study patients were identified from our American College of Surgeons-verified Level I trauma center institutional trauma database (January 2006 to October 2009). Based on our previously published data, we examined clinical data for patients aged 45 years and older, the age cutoff at which the number of comorbid conditions and chronic medication use increases noticeably and trauma mortality begins to rise."- '^ Exclusion criteria included incarceration, pregnancy, and death before leaving the trauma resuscitation area. All AG determinations performed during initial trauma evaluation were based on standardized chemistry panel. This panel consists of serum sodium, potassium, chloride, bicarbonate, blood urea nitrogen, creatinine, and glucose. All samples were processed in the hospital's central laboratory. These specimens were performed using the Beckman Coulter analyzer with standard methodology. The AG was derived from the equation in Figure 1. Detailed analysis of medical records was performed including examination of the following additional variables: patient demographics. Injury Severity Score (ISS) and other injury characteristics, admission vital signs, surgical intensive care unit (SICU) length of stay, ventilator days, complications, comorbidity-polypharmacy score,'^ mortality, discharge disposition, and functional assessment scores (Functional Outcome Measures for locomotion, expression-communication, and self-feeding)'"* on discharge. Descriptive statistics, ^ test. Student's t test, and analysis of variance were used to analyze the data. Results
A total of 711 patients aged 45 years and older were included (395 male, 316 female). Mean age for the group was 63.5 ± 13.7 years. Mean ISS for the group was 9.02 ± 8.82 (range, 1 to 75). Because it is our pattern of practice to obtain lactate and/or base excess determinations only in the most acutely injured patients, a limited sample of patients with concomitant AG and lactate/base excess was available. In that group, AG measurements correlated moderately with serum lactate (n = 33, r = 0.568, P < 0.01) and poorly with base excess (n = 57, r = 0.163, P > 0.05). Overall, increases in AG were associated with stepwise increases in ISS (Fig. 2). Elevated mortality was seen for AG 16 to 22 with further doubling of mortality for AGs greater than 22. This relation between AG and moriality was significant (x^, P < 0.01; Fig. 3). Increasing AG also correlated with morbidity and increased proportion of intensive care admissions (both, P < 0.05). Overall, the presence of one or more complications was seen in 28.6 per cent of patients with AG
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November 2013
Na + K unmeasured cations (UC) = (CL' + HCO3) + unmeasured anions (UA) Na+K- (Ct+ HCOi) = (UA-UC) and (UA-UC) is equal lo AG
FIG. 1. Mathematical formula for anion gap (AG) calculation.
