Increased Anion Gap Metabolic Acidosis

The normal gap in children under 3 years is about 12 (10-14) mEq/L and above that age is 14 (10-18) mEq/L.  A good mnemonic for the common causes of increased anion gap metabolic acidoses is MUDPILES.

The increased anions can either be made endogenously or result from exogenous administration, usually ingestion.  Endogenous anions can be organic acids such as amino acids, pyruvic acid, or lactic acid or  inorganic salts.  Excessive serum amino acids build up in a number of inborn errors of metabolism and are likely to present as a life-threatening acidosis at the time of birth or shortly after the first feeding (for example, maple syrup urine disease, isoleucine defects such as proprionic acidemia, methylmalonic acidemia).  Under anoxic conditions, cells forced into anaerobic metabolism will produce lactic acid.  In insulin deficiency (eg, starvation) ketoacidosis occurs when fatty acids are incompletely oxidized, leading to increased serum beta-hydroxybutyric acid and acetoacetic acid.  This is the basis of diabetic ketoacidosis.  If the kidneys are not working properly, the body will not be able to rid itself of its endogenous  inorganic acids such as sulfate and phosphates.  Finally, ingestion of a number of compounds such as polyethylene glycol (antifreeze), any kind of alcohol (methanol, ethanol), or salicylates will increase the gap.  In many of these ingestions, the osmolar gap will also be increased.
 

Acid-Base

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