MUDPILES mnemonic: the causes of high anion gap metabolic acidosis

What each letter stands for

M is methanol poisoning. U is uremia, the acid buildup of kidney failure. D is diabetic ketoacidosis, although alcoholic ketoacidosis belongs in the same family. P has carried several meanings: paraldehyde in older lists, now mostly replaced by propylene glycol or paracetamol, the name used outside the United States for acetaminophen.

I is iron, isoniazid, infection or inborn errors of metabolism, depending on the source. L is lactic acidosis, for example from shock or sepsis. E is ethylene glycol, the antifreeze poisoning. S is salicylates such as aspirin. MSD Manuals sorts the same causes into four families: ketoacidosis, lactic acidosis, kidney failure and toxic ingestions.

When nurses actually use it

The anion gap is a value calculated from sodium, chloride and bicarbonate that estimates acids the routine panel does not measure. When a client has a low bicarbonate and the gap is raised, MUDPILES gives a checklist of what added acid could be present. The nurse does not diagnose the cause, but knowing the list shapes what to look for and report.

That means checking glucose and ketones in a client with diabetes, watching perfusion and lactate in a septic client, asking about ingestions when an alert young adult has an unexplained acidosis, and tracking creatinine in kidney failure. Deep, rapid breathing, the compensation MSD Manuals describes as hyperpnea, is often the finding that first draws attention.

Where MUDPILES misleads or is incomplete

Several letters are out of date. Paraldehyde is rarely used today, and the I has drifted across iron, isoniazid and infection, so students memorize different lists. In 2008 Mehta, Emmett and Emmett proposed GOLDMARK in The Lancet as a modern replacement: Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure and Ketoacidosis.

GOLDMARK adds causes MUDPILES lacks, such as oxoproline, a metabolite linked to acetaminophen, and D-lactate. Both causes are rare at the bedside, but they show that any mnemonic is a starting list, not a complete one. Learn MUDPILES as a quick recall list for a raised gap, then learn the normal gap causes it cannot reach.

The biggest gap is scope. MUDPILES only covers high anion gap acidosis. Diarrhea and intestinal fistulas cause metabolic acidosis with a normal anion gap, also called hyperchloremic acidosis, and they never appear in the mnemonic. A student who reaches for MUDPILES with every low bicarbonate will miss an everyday bedside cause.

A worked exam scenario on anion gap

Hypothetical scenario, not a real exam item: a client with type 1 diabetes has had profuse diarrhea for three days. The ABG shows a low pH and low bicarbonate, the anion gap is normal, and blood glucose is only mildly raised. Which explanation fits best: diabetic ketoacidosis, salicylate toxicity, or bicarbonate loss through the gut?

Bicarbonate loss through the gut fits best. Diabetic ketoacidosis is the tempting answer because the client has diabetes and D sits in MUDPILES, but ketoacids raise the anion gap. Salicylates also raise the gap. A normal gap points away from the MUDPILES list altogether, so the nursing focus becomes fluid and electrolyte replacement as ordered while the team confirms the cause.

Sources and further reading

MSD Manual Professional Version: Metabolic Acidosis. High anion gap causes (ketoacidosis, lactic acidosis, kidney failure, toxic ingestions including methanol and ethylene glycol), normal gap causes such as diarrhea and fistulas (hyperchloremic acidosis), and compensatory hyperpnea.

Mehta AN, Emmett JB, Emmett M. GOLD MARK: an anion gap mnemonic for the 21st century. The Lancet, 2008 (PubMed record). The GOLDMARK mnemonic, its authors and its 2008 Lancet publication as a proposed update to MUDPILES.

MSD Manual Professional Version: Acid-Base Disorders. Stepwise acid-base interpretation and the definition of acidosis as acid accumulation or alkali loss.