A 35-year-old woman is brought to the hospital 4 hours after ingesting an unknown quantity of antifreeze (ethylene glycol) from a container she mistook for water in her garage in Delhi. She is alert but confused, with a respiratory rate of 26/min and deep breathing. Serum creatinine is 2.8 mg/dL (baseline 0.8), and urinalysis shows calcium oxalate crystals. Arterial blood gas: pH 7.15, HCO₃⁻ 10 mEq/L, PaCO₂ 32 mmHg. What is the immediate next step in management?

Explanation

## Ethylene Glycol Poisoning: Acute Management **Key Point:** Ethylene glycol poisoning requires IMMEDIATE dual intervention: fomepizole to block toxic metabolite formation AND hemodialysis to remove both the parent compound and its toxic metabolites (glycolic acid, glyoxalic acid, oxalic acid). ### Why This Patient Needs Urgent Intervention **High-Yield:** The presence of **calcium oxalate crystals in urine + acute kidney injury + high anion gap metabolic acidosis** indicates that ethylene glycol has already been metabolized to oxalic acid, causing: - Acute tubular necrosis (ATN) - Hyperoxaluria with crystal deposition - Irreversible renal damage if not treated urgently ### Pathophysiology of Ethylene Glycol Toxicity ```mermaid flowchart TD A[Ethylene Glycol Ingestion]:::outcome --> B[Alcohol Dehydrogenase]:::action B --> C[Glycolaldehyde]:::outcome C --> D[Glycolic Acid]:::outcome D --> E[Glyoxalic Acid]:::outcome E --> F[Oxalic Acid]:::outcome F --> G[Calcium Oxalate Crystals]:::urgent G --> H[Acute Kidney Injury]:::urgent F --> I[High Anion Gap Acidosis]:::urgent A --> J[Fomepizole]:::action J --> K[Blocks ADH]:::action K --> L[Prevents Metabolite Formation]:::outcome L --> M[Preserves Renal Function]:::outcome ``` ### Three Phases of Ethylene Glycol Toxicity | Phase | Timing | Features | Mechanism | |-------|--------|----------|----------| | **Phase 1 (Neurological)** | 0–12 hours | CNS depression, ataxia, confusion, seizures | Parent compound (ethylene glycol) | | **Phase 2 (Cardiopulmonary)** | 12–24 hours | Pulmonary edema, tachycardia, hypertension | Glycolic acid accumulation | | **Phase 3 (Renal)** | 24–72 hours | Acute kidney injury, oliguria, calcium oxalate crystals | Oxalic acid deposition in tubules | **Clinical Pearl:** This patient is transitioning from Phase 1 to Phase 2–3 (4 hours post-ingestion with already elevated creatinine and crystals). She is at imminent risk of irreversible renal failure. ### Management Algorithm ```mermaid flowchart TD A[Ethylene Glycol Poisoning Suspected]:::outcome --> B{Time since ingestion?}:::decision B -->|< 6 hours| C[Fomepizole STAT]:::action B -->|Any time| D[Check: Osmolal gap, Anion gap, Cr, Urinalysis]:::action C --> E[Hemodialysis if:]:::decision E -->|Severe acidosis| F[pH < 7.25]:::urgent E -->|Renal failure| G[Cr > 2.0 or oliguria]:::urgent E -->|Metabolites present| H[Glycolic acid detected]:::urgent E -->|Crystals| I[Calcium oxalate in urine]:::urgent F --> J[Initiate Hemodialysis]:::action G --> J H --> J I --> J J --> K[Continue Fomepizole]:::action K --> L[Supportive Care + Monitoring]:::action ``` ### Fomepizole (4-Methylpyrazole) Dosing **High-Yield:** Fomepizole is the **antidote of choice** — it competitively inhibits alcohol dehydrogenase with 1000× higher affinity than ethanol. - **Loading dose:** 15 mg/kg IV over 30 minutes - **Maintenance:** 10 mg/kg IV every 12 hours for 4 doses, then 15 mg/kg every 12 hours until ethylene glycol levels <20 mg/dL or osmolal gap normalizes - **Advantage over ethanol:** No CNS depression, no hypoglycemia risk, more predictable kinetics ### Why Hemodialysis Is Mandatory Here 1. **Removes parent compound** — ethylene glycol is water-soluble and dialyzable 2. **Removes toxic metabolites** — glycolic acid, glyoxalic acid, oxalic acid 3. **Corrects severe acidosis** — pH 7.15 is life-threatening 4. **Prevents progressive renal failure** — crystals already forming 5. **Removes fomepizole** — fomepizole is also dialyzable; dosing must be adjusted during dialysis **Mnemonic: FOMEPIZOLE = "FOr MEthanol and Polyol (ethylene glycol) poisoning, ZOLE (inhibitor)"** ### Why Other Options Are Inadequate - **Activated charcoal:** Ethylene glycol is not absorbed by charcoal; ineffective - **Gastric lavage:** Only useful if within 1–2 hours of ingestion; too late here - **Sodium bicarbonate alone:** Treats acidosis symptomatically but does NOT remove the toxin or prevent renal damage; must be combined with fomepizole and dialysis **Warning:** Delaying hemodialysis in this patient risks irreversible acute kidney injury requiring long-term dialysis or transplantation. [cite:Forensic Medicine & Toxicology, Reddy 33e Ch 22; Harrison 21e Ch 472; Robbins 10e Ch 9]