Normal Anion Gap Metabolic Acidosis
Normal anion gap metabolic acidosis is also termed "hyperchloremic" metabolic
acidosis, and results from loss of water and bicarbonate with consequent
concentration of the remaining chloride. The classic cause in children
is diarrhea. In severe diarrhea, bicarbonate concentrations of up
to 50mEq/L are seen in the copious diarrheal fluids.
Other possible causes of normal anion gap metabolic acidosis include:
-
Exposure of ileal mucosa to urine (as either the intentional result of
a surgical procedure or in the event of fistula).
-
Renal tubular acidosis
of various types.
-
Administration of carbonic anhydrase inhibitors
-
Expansion of ECF with chloride-rich fluid (eg, NS) with dilution of bicarbonate
(expansion acidosis)
-
Administration of HCl or metabolic equivalents (ammonium chloride, arginine
hydrochloride, etc.)
Unmeasured cations can falsely narrow the anion gap, making an otherwise
widened gap appear normal. For example, if ammonium were present
in high concentration it could disguise an increased
anion gap metabolic acidosis.
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Last modification: April 30, 1998
