The most appropriate additional management intervention in this patient is intravenous sodium bicarbonate therapy. He has findings typical of ethylene glycol intoxication, with evidence of central nervous system depression presumably due to the alcohol, an increased anion gap metabolic acidosis of 28 mEq/L (28 mmol/L), an osmolal gap of 27 mOsm/kg H₂O, and kidney failure likely resulting from deposition of calcium oxalate crystals in the renal tubules. Because the laboratory confirmation of ethylene glycol intoxication may take days, empiric therapy for patients with likely ethylene glycol intoxication is recommended pending confirmation. Treatment usually consists of intravenous hydration, fomepizole (a competitive inhibitor of alcohol dehydrogenase), and hemodialysis to clear both the parent alcohol as well as the toxic metabolites. Intravenous sodium bicarbonate therapy is also recommended in suspected ethylene glycol or methanol ingestion when the blood pH is below 7.30. This is because the toxic metabolites of ethylene glycol (glycolate, glyoxylate, and oxalate) and methanol (formate) penetrate tissues more effectively when in the neutral state, which is increased by an acidic blood pH. Bicarbonate is given to normalize the blood pH and maximize formation of the ionized forms of the associated toxic metabolites.

Both ethylene glycol and methanol are completely absorbed from the gastrointestinal tract, with peak serum levels occurring within 1 to 2 hours of ingestion. Therefore, gastric decontamination, such as with activated charcoal, is not usually performed unless the timing of a large ingestion is known and decontamination can be performed within 1 hour.

Intravenous ethanol was traditionally used as a competitive inhibitor of alcohol dehydrogenase; it is effective because this enzyme has greater affinity for ethanol than for ethylene glycol or methanol. However, fomepizole has been found to be a superior therapy to ethanol, is easier to administer, and has fewer side effects. Although ethanol is a reasonable second-line therapy, there is no benefit to coadministration of fomepizole and ethanol.

Given the patient's possible ingestion of ethylene glycol with an associated low blood pH, not providing bicarbonate therapy would be inappropriate.