Dr. Michael McCrea, our Associate Program Director, recently gave us a lecture about toxic alcohols. Here are the learning pearls from that lecture:
The first thing to learn with respect to toxic alcohols are the:
Gaps
Anion Gap = [Na] - ([Cl] + [HCO3]), Normal </= 12 Causes of elevated anion gap: "CAT MUDPILES". Among these are both methanol and ethylene glycol (note: ethanol and isopropyl alcohol themselves do not elevate the anion gap)
Osmolar Gap = Measured osmolarity - Calculated osmolarity, Normal </=12 Calculated osmolarity = 2[Na] + [Glucose]/18 + [BUN]/2.8, Normal 285-295 Causes of elevated osmolar gap: "ME DIE" mnemonic Tip: multiply the osmolar gap by the conversion factor* to estimate the amount of toxic alcohol in mg/dL
The anion gap and osmolar gap can give you valuable information about what substance has been ingested, and roughly how much.
Methanol
Sources: windshield washer fluid, solvents, sterno cooking fuel, moonshine, pesticide
Toxic metabolite, Formic Acid, causes symptoms
Elevated anion gap AND osmolar gap
Symptoms: inebriation, blindness (directly toxic to the optic disc and optic nerve), "snowstorm" vision. Basal ganglia hemorrhages.
Toxic level is >20mg/dL
Treatment: - Folate: cofactor for formic acid metabolism. Goal is to get rid of the toxic metabolite quickly. - Give 1-2mEq/kg of Sodium Bicarbonate if pH<7.3 - Ethanol: oral or IV to achieve ethanol level of 100-150mg/dL • Oral: 0.8mg/kg 20% EtOH solution in diluted orange juice, then 80mg/kg/hr • IV: 10mL/kg 10% EtOH solution in D5W over 60 minutes, then 1mL/kg/hr of 10% EtOH solution (titrate to serum ethanol levels) - Fomepizole: 8000x affinity for alcohol dehydrogenase • IV: 15mg/kg, then 10mg/kg every 12 hours for 4 doses, then 15mg/kg every 12 hours
Indications for dialysis: - Intractable acidosis - Acute renal failure - ANY visual symptoms - Methanol >50mg/dL
Ethylene Glycol
Sources: radiator antifreeze
Toxic metabolites: - Glycolic Acid: exerts its toxicity through oxalic acid - Glyoxylic Acid: exerts its toxicity through oxalic acid - Oxalic Acid: causes hypocalcemia and QTc prolongation; binds with calcium to form calcium oxalate crystals that precipitate in the kidneys causing renal failure
Elevated anion gap AND osmolar gap
Symptoms: inebriation, neurologic effects (coma, seizures, cranial nerve deficits), cardiovascular effects (tachycardia, hyperventilation, ARDS, heart failure), oliguria, flank pain
Toxic level is >20mg/dL
Treatment: - Thiamine: 100mg IV daily until symptoms or acidosis resolves; facilitates breakdown of toxic metabolite - Pyridoxine (Vitamin B6): 10-25mg IV daily; facilitates breakdown of toxic metabolite - Sodium bicarbonate, Ethanol, and Fomepizole as above
Indications for dialysis (similar to methanol above): - Intractable acidosis - Acute renal failure - ANY visual symptoms - Ethylene glycol >50mg/dL
Extra Pearls
Common elements for both methanol and ethylene glycol: - Elevated anion gap - Elevated osmolar gap - Toxic level is >20mg/dL - Dialysis level is >50mg/dL, other dialysis indications are similar
Buzz words: - Methanol: formic acid; blindness or "snowstorm" vision; treat with folate and ethanol or fomepizole, +/-Sodium bicarb - Ethylene glycol: antifreeze; oxalic acid, glyoxylic acid, glycolic acid; treat with thiamine, pyridoxine, and ethanol or fomepizole, +/-Sodium bicarb
FOUR things give elevated anion gap AND elevated osmolar gap - Methanol - Ethylene Glycol - Alcoholic ketoacidosis if ethanol is still high - Diabetic ketoacidosis if glucose is very high
References and other resources to check out:
Episode 43 - Alcohols by Lauren Westafer and Jeremy Faust on FOAMCast.org
Toxic Alcohol Ingestion by Edward Burns on Life in the Fast Lane
Hassanian-Moghaddam H, Zamani N. A Brief Review on Toxic Alcohols. Iranian Journal of Kidney Diseases. 2016;10:344-50.