Prognostic Value of an Initial Strong Ion Gap in Critically Ill Patients at the Emergency Department

ABSTRACT

PURPOSE: This study was performed to determine whether the anion gap, the base excess, the lactate, and the strong ion gap obtained in the emergency department correlate with the prognosis and whether the strong ion gap is the most useful marker compared to the prognostic ability of the anion gap, the base excess, and the lactate. METHODS: We reviewed the records of 106 patients admitted to the intensive care unit via the emergency department. We measured the anion gap, the base excess, and the lactate and we calculated strong anion gap by using a formula. We divided the patients into survivors and nonsurvivors and compared the prognostic abilities of the four variables by using the Student's t-test and receiver operator characteristic curves. RESULTS: The mean age of the patients was 67+/-14, and the numbers of males and females were similar (58 males vs 48 females). The number of survivors was 92 (86.7%), and that of nonsurvivors was 14 (3.2%). The anion gap ( 24.8+/-8.8 vs. 16.4+/-4.8 mmol/L, p value=0.000), the base excess (-11.9+/-8.7 vs. -3.49+/-6.5 mmol/L, p value = 0.001), the lactate (9.1+/-7.7 vs. 4.5+/-3.1 mmol/L, p value = 0.011 ) and the strong ion gap (16.6+/-3.6 vs. 10.9+/-3.7, p value=0.000) of the nonsurvivors were higher. All of the four varibles were associated with the prognosis, but among them, the strong ion gap discriminated most strongly with an area under the receiver operator characteristic curve of 0.866 (95% confidence interval, 0.787 to 0.92). CONCLUSION: The initial emergency-department acid-base variables, the anion gap, the base excess, the lactate and the strong ion gap have prognostic abilities, but the strong ion gap is the variable that most strongly predicts of mortality.