This patient's encephalopathy, high anion gap, and elevated osmolal gap are most consistent with methanol (wood alcohol) or ethylene glycol (antifreeze) ingestion. This patient's anion gap is 30 mEq/L (30 mmol/L), and the upper limit of normal is typically 10 mEq/L (10 mmol/L). The osmolal gap is the difference between calculated and measured plasma osmolality. Plasma osmolality (mOsm/kg H₂O) is calculated as follows:

2 × serum sodium (mEq/L) + plasma glucose (mg/dL)/18 + blood urea nitrogen (mg/dL)/2.8

The measured osmolality is 325 mOsm/kg H₂O. The calculated osmolality is 295 mOsm/kg H₂O. The osmolal gap is 30 mOsm/kg, and the normal range is less than 10 mOsm/kg. Methanol is converted to formic acid, which is toxic to the retina of the eye. Ethylene glycol is converted by alcohol dehydrogenase to oxalic acid, which crystalizes in renal tubules and causes kidney injury. Conversion to toxic metabolites and clearance of these alcohols is greatly diminished by ethanol or intravenous fomepizole. All alcohols can be removed rapidly with dialysis.

Patients with isopropyl alcohol poisoning present with intoxication and an elevated osmolal gap, but they do not have an increased anion gap acidosis as is seen in this patient.

Salicylate toxicity is another cause of increased anion gap acidosis, encephalopathy, and vomiting. However, it does not cause elevation of the osmolal gap, as is seen in this patient.

Serotonin syndrome is a cause of fever and encephalopathy, but it typically manifests with agitation, muscle rigidity, and hyperreflexia, none of which are present in this patient. Serotonin syndrome also would not explain this patient's increased anion gap acidosis and osmolal gap. This patient's fever is most likely related to an aspiration event.