Toxicology dogmalysis: the osmolal gap

I've been checking the serum osmolal gap on patients with toxic ingestion for years. However, the osmolal gap has yet to crack a case for me. There have been lots of patients with elevated osmolal gaps due to uremia or ketoacidosis. Meanwhile, the cases of ethylene glycol or methanol intoxication which I have encountered have been diagnosed based on other features (e.g., history of antifreeze ingestion, anion gap acidosis, crystalluria).

Diagnostics: Toxic Alcohols

The term “toxic alcohols” refers to a group of substances which, when metabolized, form toxic metabolites that can lead to organ dysfunction or death. Of the many toxic alcohols, the most commonly ingested and therefore most clinically relevant are methanol, ethylene glycol, propylene glycol, and isopropanol.

Episode 129.0 – Toxic Alcohols

Suspect a toxic alcohol in any patient with a large osmol gap or a large anion gap metabolic acidosis and consider treating these patients empirically.

Ethylene glycol & methanol poisoning

Osmolal gap has traditionally been used as a screening test for toxic alcohol ingestion. However, this chapter will argue that it should be abandoned. This is a bit controversial, but there is a considerable amount of evidence that the osmolal gap is unhelpful. Furthermore, many toxicologists have been saying this for a long time.

Methanol or Ethanol Poisoning? Correct Diagnosis Influences Treatment

Methanol intoxication may regularly be seen endemically or sometimes epidemically because alcohol may contain methanol in countries where alcohol consumption is prohibited or the price of the commercially available alcohol is high.

Toxic Alcohol Ingestion

Serum toxic alcohol concentrations, while ultimately necessary to confirm the diagnosis and guide ongoing management, are unlikely to be available within the first few hours of a suspected toxic alcohol ingestion, therefore diagnosis is based on the history, clinical features and surrogate biochemical markers such as blood gases, osmolar gap and anion gap.

Toxic Alcohols

When it comes to understanding why toxic alcohols are poisonous, we must look at their metabolism. Beyond intoxication and CNS depression, toxic alcohols in of themselves do not possess significant toxicity. The toxicity of these compounds comes from their organic acid metabolites. They result in the hallmark anion gap metabolic acidosis while also having unique end organ effects.

Toxic Alcohols

Plasma Osmolal Gap... Note: this tool is not helpful in late presentations as the metabolized forms of the different alcohols do not contribute to the osmolal gap. The calculated gap will be falsely low in late-stage poisoning.

Toxic Alcohols – Minding the Gaps

Alcohol is everywhere, and inevitably inebriated people show up at your ED with a myriad of medical and psychiatric problems – we’re all familiar with these patients. Or they are simply very drunk. And most of them just need to sober up and can be sent home.