Acute Care 24: Causes of Anion and Non-Anion Gap Acidosis
Presence
of an increased anion gap signifies a base deficit and a metabolic
acidosis. Normal anion gap is 12 ± 2-4 mEq/L. Anion gap acidosis means
the value is above the normal
-
Anion gap = NA+ -[Cl- +HCO3-]=unmeasured anions – unmeasured cations
-
Normal sodium value = 140 mEq/L ± 4 mEq/L
-
Normal chloride = 100 if the sodium is 140 (roughly Na+ divided by 1.4).
-
An abnormal chloride level is a red flag for some sort of acid/base abnormality, even if HCO3- is normal.
- Normal HCO3- = 22 - 26 mEq/L
To recall causes of anion
gap acidosis, use the mnemonic
MUDPILES:
M—Methanol
U—Uremia
D—Diabetic
ketoacidosis
P—Paraldehyde
I—Iron or
isoniazide, inhalants (CO, CN, H2S)
L—Lactic acid
E—Ethanol
(ketoacidosis), ethylene glycol
S—Salicylates,
solvents (toluene), starvation (ketoacidosis)
To recall causes of
non-anion gap acidosis, use the mnemonic
USED CARP:
U—Ureteroenterostomy
S—Small
bowel fistula
E—Extra
chloride
D—Diarrhea
C—Carbonic
anhydrase inhibitors
A—Adrenal
insufficiency
R—Renal
tubular acidosis
P—Pancreatic
fistula