Initial pH, base deficit, lactate, anion gap, strong ion difference, and strong ion gap predict outcome from major vascular injury*

Abstract

This study determines whether acid-base data obtained in the emergency department correlate with outcome from major vascular injury. Observational, retrospective record review of trauma patients requiring vascular repair (torso or extremity, January 1988 to December 1997). Data included age, Injury Severity Score, injury mechanism, survival, laboratory profiling, calculated anion gap, strong ion difference, and strong ion gap. Patients were divided into survivors and nonsurvivors with comparison by Student’s t-test; significance was assumed for p ≤ .05. Multivariate logistic regression was used for further analysis of univariate predictors of mortality, and receiver operator characteristic curves were generated for mortality from each variable. Urban level I trauma facility. Trauma patients requiring vascular repair of torso or extremity injury. None. Both nonsurvivors (n = 64) and survivors (n = 218) were similar with respect to age (31 ± 9 vs. 31.5 ± 10.5, p = 0.15) and injury mechanics (81% penetrating in survivors vs. 83% penetrating in nonsurvivors, p = .71). Non-survivor Injury Severity Score exceeded that of survivors (27.5 ± 7.8 vs. 12.4 ± 9.4, p < .001). Nonsurvivor pH (7.06 ± 0.15 vs. 7.34 ± 0.08, p < .001) and apparent strong ion difference (31.38 ± 4.39 vs. 37.53 ± 3.86, p < .001) were significantly lower, whereas nonsurvivor standard base excess (−17.9 ± 5.1 vs. −2.9 ± 4.4 mEq/L, p < .001), lactate (11.1 ± 3.6 vs. 3.6 ± 1.5 mmol/L, p < .001), anion gap (28.2 ± 4.1 vs. 15.6 ± 3.1, p < .001), and strong ion gap (10.8 ± 3.2 vs. 2.4 ± 1.8, p < .001) were higher. All but one nonsurvivor had initial emergency department pH ≤7.26, standard base excess ≤ −7.3 mEq/L, lactate ≥5 mmol/L, and strong ion gap ≥5 mEq/L. All of the acid-base descriptors were strongly associated with outcome, but the strong ion gap discriminated most strongly with an area under the receiver operator characteristic of 0.991 (95% confidence interval, 0.972– 0.998). The initial emergency department acid-base variables of pH, base deficit, lactate, anion gap, apparent strong ion difference, and strong ion gap discriminate survivors from non-survivors of major vascular injury. The strong ion gap is most strongly predictive of mortality following major vascular trauma.