In this month’s Best Case Ever on EM Cases Dr. Ross Claybo and Dr. Keerat Grewal tell the story of a patient with a complicated anion gap metabolic acidosis. We discuss how to sort through the differential diagnosis with a better mnemonic than MUDPILES, the controversy around administering sodium bicarbonate for metabolic acidosis, the indications for fomepizole and the value of taking time to to build a therapeutic relationship with your ED patients.

 

Podcast: Play in new window | Download (Duration: 20:45 — 19.0MB)

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Podcast production and sound design by Anton Helman. Show notes by Anton Helman, March 2017

The MUDPILES mnemonic for anion gap metabolic acidosis is out of date

Why?

  • Metabolic acidosis due to paraldehyde overdose is exceedingly rare
  • Iron and isoniazid are just two of many drugs and toxins that cause hypotension and lactic acidosis (isoniazid can also generate a component of ketoacidosis).
  • Three “newer” anion-gap-generating acids have been recognised recently:
    • D-lactic acid, which can occur in some patients with short bowel syndromes.
    • 5-oxoproline (or pyroglutamic acid) associated with chronic acetaminophen use.
    • Propylene glycol infusions – solvent used for several IV medications including lorazepam and phenobarbital.

 

The GOLDMARK mnemonic for anion gap metabolic acidosis is more useful

GOLDMARK mnemonic for anion gap metabolic acidosis
Glycols (ethylene glycol & propylene glycol)

Oxoproline (metabolite of acetaminophen)

L-lactate

D-lactate (acetaminophen, short bowel syndrome, propylene glycol infusions for lorazepam and phenobarbital)

Methanol

ASA

Renal Failure

Ketoacidosis (starvation, alcohol and DKA)

Download PDF of GOLDMARK mnemonic

 

Osmolar Gap common differential diagnosis

Ketoacids (DKA, AKA, starvation ketosis)

Alcohols

Sepsis

Ischemia

 

Sodium bicarbonate for metabolic acidosis: Still controversial

The indcations for sodium bicarb for metabolic acidosis are controversial with no evidence in the human literature that it decreases mortality. The —traditional treatment is based on adverse effects of metabolic acidosis on animal subjects at pH less than 7.1 including acute decrease in cardiac contractility, arteriole dilatation and hypotension, decreased O2 delivery to tissues, arrhythmias and decreased immunity. This needs to be weighed against the potential adverse effects of sodium bicarbonate administration, which include increased CSF intracellular acidosis, volume overload, increased osmolarity and decreased ionized Ca.

Drs Helman, Claybo and Grewal have no conflicts of interest to declare

References

Mehta AN, Emmett JB, Emmett M. GOLD MARK: an anion gap mnemonic for the 21st century. Lancet. 2008;372(9642):892.

Forsythe SM, Schmidt GA. Sodium bicarbonate for the treatment of lactic acidosis. Chest. 2000;117(1):260-7.

 

Other FOAMed Resources on Anion Gap Metabolic Acidosis

Rob Orman and Sean Nordt discuss the nuances of working up an anion gap metabolic acidosis on ERCAST