MUDPILES or GOLDMARK for the unmeasured anions
Expansion
MUDPILES:
- M - Methanol
- U - Uraemia
- D - Diabetic ketoacidosis
- P - Paraldehyde, Propylene glycol
- I - Iron, Isoniazid
- L - Lactic acidosis
- E - Ethylene glycol
- S - Salicylates
The more modern GOLDMARK reflects what is actually seen: Glycols, Oxoproline (from chronic paracetamol), L-lactate, D-lactate (short bowel), Methanol, Aspirin, Renal failure, Ketoacidosis.
In practice, the overwhelming majority are lactate, ketones and renal failure, so measure those three first.
Ketoacidosis has three forms: diabetic, alcoholic (with a normal or low glucose, after a binge followed by vomiting and starvation) and starvation (mild).
Lactic acidosis: type A from tissue hypoperfusion or hypoxia, being shock, sepsis, ischaemia and severe anaemia; type B without hypoperfusion, from metformin, liver failure, malignancy, thiamine deficiency, beta agonists and some antiretrovirals.
The osmolar gap is the next step when the anion gap is unexplained:
Calculated osmolality = 2 x sodium + urea + glucose
A gap over 10 mosmol/kg between measured and calculated suggests an unmeasured osmole, classically methanol or ethylene glycol, and also ethanol, mannitol or propylene glycol. Early in toxic alcohol poisoning the osmolar gap is high and the anion gap normal; later the reverse, as the parent alcohol is metabolised to acid.
Normal anion gap (hyperchloraemic) acidosis is a different list, remembered as gastrointestinal bicarbonate loss (diarrhoea, fistula, ileostomy), renal tubular acidosis, carbonic anhydrase inhibitors, and large volume saline infusion.