Anion gap, anion gap corrected for albumin, base deficit and unmeasured anions in critically ill patients: implications on the assessment of metabolic acidosis and the diagnosis of hyperlactatemia.
BACKGROUND
Base deficit (BD), anion gap (AG), and albumin corrected anion gap (ACAG) are used by clinicians to assess the presence or absence of hyperlactatemia (HL). We set out to determine if these tools can diagnose the presence of HL using cotemporaneous samples.


METHODS
We conducted a chart review of ICU patients who had cotemporaneous arterial blood gas, serum chemistry, serum albumin (Alb) and lactate(Lac) levels measured from the same sample. We assessed the capacity of AG, BD, and ACAG to diagnose HL and severe hyperlactatemia (SHL). HL was defined as Lac > 2.5 mmol/L. SHL was defined as a Lac of > 4.0 mmol/L.


RESULTS
From 143 patients we identified 497 series of lab values that met our study criteria. Mean age was 62.2 +/- 15.7 years. Mean Lac was 2.11 +/- 2.6 mmol/L, mean AG was 9.0 +/- 5.1, mean ACAG was 14.1 +/- 3.8, mean BD was 1.50 +/- 5.4. The area under the curve for the ROC for BD, AG, and ACAG to diagnose HL were 0.79, 0.70, and 0.72, respectively.


CONCLUSIONS
AG and BD failed to reliably detect the presence of clinically significant hyperlactatemia. Under idealized conditions, ACAG has the capacity to rule out the presence of hyperlactatemia. Lac levels should be obtained routinely in all patients admitted to the ICU in whom the possibility of shock/hypoperfusion is being considered. If an AG assessment is required in the ICU, it must be corrected for albumin for there to be sufficient diagnostic utility.
Chawla
Lakhmir S
LS
Department of Critical Care Medicine and Anesthesiology, George Washington University Medical Center, Washington, DC, USA. lchawla@mfa.gwu.edu
Shih
Shirley
S
Davison
Danielle
D
Junker
Christopher
C
Seneff
Michael G
MG
D000136:Acid-Base Equilibrium; D000140:Acidosis, Lactic / Q000097:blood* / Q000175:diagnosis* / Q000453:epidemiology; D000328:Adult; D000368:Aged; D000418:Albumins / Q000032:analysis*; D000838:Anions / Q000097:blood*; D001774:Blood Chemical Analysis / Q000379:methods; D015331:Cohort Studies; D003422:Critical Care; D016638:Critical Illness; D003937:Diagnosis, Differential; D004219:District of Columbia / Q000453:epidemiology; D005260:Female; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012372:ROC Curve
D000418:Albumins; D000838:Anions; D019344:Lactic Acid