Episode 58: Toxic alcohols with Jerry Snow

We look at evaluating the patient with encephalopathy and unexplained anion gap, including the workup and treatment of toxic alcohol poisoning, with guest Dr. Jerry Snow (@ToxicSnowEM), medical toxicologist and director of the toxicology fellowship at Banner University Medical Center in Phoenix.

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Takeaway lessons

* A toxicologic exposure should be suspected, even without a clear story, based on the prehospital scene. EMS or family reports of chemicals, pill bottles, etc should be elicited. Prescribed medications should be questioned, as well as any other meds that could be available to the patient, such as older meds, current and older meds prescribed to family members, and supplements.

* Physical exam maneuvers high-yield for tox diagnosis include the pupillary exam, skin exam (diaphoretic vs dry), and examination of muscle tone and deep tendon reflexes.

* Laboratory clues of tox diagnoses include an elevated anion gap in the absence of common causes (lactate, ketones, uremia), as most of the remaining causes of a gap are toxins.

* Elevated osmolal gaps should also be investigated, although considered an insensitive test for most toxins. A serum chemistry, as well as salicylate and acetaminophen levels, should be sent routinely. An ECG should be checked for findings like interval prolongation and morphology changes.

* “Normal” osmolality varies too much for a low osm gap to be useful, but a clearly elevated gap is diagnostically helpful, particularly when its presence/absence is compared with the presence/absence of an anion gap.

* The most common source of methanol ingestion in the US is windshield wiper fluid; it’s also present in poorly-distilled homemade moonshine, hand sanitizer, model car fuel, food-warmer fuel, lacquer and paint thinner, and many others. For ethylene glycol, the most common US source is automotive antifreeze. In both cases, these are usually intentional ingestions.

* Toxic alcohol levels, namely methanol and ethylene glycol levels, are send-out tests in most centers and result too slowly to be useful in the early stages. You will need to treat empirically based on suspicion and perhaps based on osmolar gap.

* Urine tox screens rarely change management, and may lead to missed diagnoses due to anchoring. Many substances are not tested, and positive tests (e.g. for opioids or benzodiazepines)—even for substances that may explain the clinical picture—can be false positives. Even true positives do not rule out the presence of another medical or even a second toxicologic cause. Correlate cautiously with the clinical picture (e.g. opioid toxicity may not explain encephalopathy in a patient with normal pupils and hyperventilation), or simply don’t send it to begin with.

* Acute iron overdose can cause anion gap acidosis, GI symptoms including bleeding, and shock and an overal critically ill presentation.

* Ethanol has fallen out of favor for treatment of toxic alcohols, although it does work; it is logistically challenging, requiring frequent lab checks to ensure therapeutic levels, central venous access, and other fuss; complications are much higher than with fomepizole. It’s good for low-resource settings that may not have the more expensive fomepizole, however,