Anion and Osmolar Gaps

Formulas
	⁃	AG = NA - Cl - HCO3 (normal 8-12 unless albumin is low)
	⁃	Osm Calculated = 2Na + BUN/2.8 + glu/18 + EtOH/4.6
	⁃	Osm Gap = Osm measured - Osm Calculated (normal less than 10)

AG Acidosis (MUDPILES CROK)
	•	Methanol 
	⁃	vision changes and movement disorder
	⁃	Treat with ethanol or fomepizole therapy
	•	Uremia
	•	DKA 
	•	Paraldehyde or Phenformin or Propylene glycol
	⁃	Paraldehyde is discontinued psych and seizure medication and used in some industries as a solvent. Strong mouth odor.
	⁃	Phenformin - cousin to metformin that is off the market due to lactic acidosis
	⁃	Propylene glycol
	⁃	commonly used solvent for ativan, phenobarbital, etc
	⁃	Metabolized to lactate (d and l) 
	•	Iron or Isoniazid
	•	Lactate (including d-lactate in short gut syndrome)
	•	Ethanol or Ethylene Glycol
	⁃	Ethylene Glycol
	⁃	Typically as osmolar gap
	⁃	Calcium oxalate crystals in urine
	⁃	Treat with ethanol or fomepizole therapy
	•	Salicylates
	•	Others
	⁃	Cyanide (elevated venous oxygenation)
	⁃	Rhabdo
	⁃	Oxoproline (chronic tylenol use in malnutrition females)
	⁃	Ketosis from starvation (rare)

Osm Gap
	⁃	Very common
	⁃	“alcohols, sugars, lipids, proteins”
	⁃	Alcohol
	⁃	Ethanol, methanol, ethylene glycol, acetone, isopropyl alcohol, prophylene glycol
	⁃	Sugars
	⁃	Mannitol and sorbitol
	⁃	Lipids
	⁃	Hypertriglyceridemia
	⁃	Proteins
	⁃	Walderström’s or other causes of hypergammaglobinemia

Differentiation Among Ingestions
	⁃	Methanol, Ethylene glycol, and Propylene Glycol
	⁃	Classically reported as AG acidosis with osmolar gap without lactate (early)
	⁃	Can have lactate due to organ failure or lab error
	⁃	May present as late with lactic acidosis with no osmolar gap
	⁃	Ethylene glycol: Urine fluorescence and oxalate crystals should be explored but are poor markers
	⁃	Propylene Glycol is over used instead of ethylene glycol in antifreeze and is safer if ingested.
	⁃	Propylene Glycol toxicity is rarely seen except when in high doses drips when used as carrier (such as ativan)
	⁃	If considered, STAT measurements
	⁃	Treatment
	⁃	Stabalization, bicarb, fomepizole, HD, folic acid, thiamine, pyridoxine
	⁃	HD required for high anion gap acidosis or organ failure
	⁃	HD considered empirically for high AG acidosis with OSM gap
	⁃	Isopropyl alcohol and Acetone
	⁃	Osmolar gap without AG acidosis
	⁃	No vision changes or renal failure
	⁃	Isopropyl converts to acetone in the blood
	⁃	Urine and blood ketones detected but B hydroxybutyrate negative
	⁃	Typically supportive therapies