A 28-year-old woman is admitted to a tertiary care hospital in Mumbai with a 2-hour history of nausea, vomiting, abdominal pain, and altered consciousness. She had ingested an unknown quantity of antifreeze fluid 4 hours prior. Laboratory investigations reveal: pH 7.22, HCO₃⁻ 10 mEq/L, anion gap 18, serum calcium 6.2 mg/dL (low), and urine microscopy shows needle-shaped crystals. Serum osmolality is 310 mOsm/kg. What is the most appropriate immediate intervention?