My Approach to Diagnosing Acid Base Disturbances

ACID-BASE DISTURBANCES

7 Steps to diagnosing acid-base disturbances

  1. Is this acidemia or alkalemia? – Look at the pH.
  2. Is the primary disorder metabolic or respiratory?
  3. Is the degree of compensation appropriate? “A substantially reduced or excessive level of compensation is indicative of a mixed acid-base disorder”.
  4. Is the anion gap(AG) elevated or not? The Anion Gap is only needed for metabolic disorders. Note that having a high AG always means there is a primary do that has caused the high AG. Compensation doesn’t raise AG. See DDx of HAGMA and NAGMA.
  5. If the AG is high (i.e. HAGMA), one is obliged to calculate the delta-ratio (delta-delta) or delta gap to screen for the presence of additional acid-base abnormalities (called mixed metabolic acid-base disorders). One must figure out whether those anions have been solely responsible for the acidosis, or whether another (non-anion-gap) cause is hiding in the background. Also for HAGMA, test for ketones, and if they are negative, calculate the osmolal gap to help identify the other causes of HAGMA.
  6. For non-anion gap metabolic acidosis, check the urine anion gap.
  7. Identify the clinical diagnosis. What is the underlying cause(s) of each disorder? How do we address it?

HAGMA= High AG Metabolic Acidosis; NAGMA=Normal AG Metabolic Acidosis.

“Elevated AG usually represents abnormal accumulation of either endogenous or exogenous unmeasured anions and indicates a primary disorder (a metabolic acidosis), regardless of the pH or the serum bicarbonate (HCO3–)“A

 

References / Resources

A) Tsapenko, Mykola V. “Modified delta gap equation for quick evaluation of mixed metabolic Acid-base disorders.” Oman medical journal vol. 28,1 (2013): 73-4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3562975/

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