Acetylsalicylic Acid (Aspirin) Poisoning

Clinical assessment

Based on history of ingestion (type, amount, time - note delayed absorption with enteric-coated preps). Characteristic clinical features (tinnitus, hyperpnea, altered mental status, hyperthermia). Assessment of acid-base status is crucial.

Investigations

• Serum Salicylate Level: Essential. Obtain level at presentation and serially every 2-4 hours until peaking and declining. Peak level may be delayed 4-6 hours or longer with enteric-coated or massive ingestions. Use Done nomogram for acute ingestions only (less reliable now, interpret level with clinical picture and acid-base status). Level >30mg/dL (2.2mmol/L) usually symptomatic; >80-100mg/dL (5.8-7.2mmol/L) often severe.
• Arterial Blood Gas (ABG) or Venous Blood Gas (VBG with electrolytes): CRITICAL for assessing acid-base status (respiratory alkalosis, metabolic acidosis, mixed disorder) and guiding therapy (bicarbonate).
• Electrolytes: Check potassium (often low), calculate anion gap (usually elevated in metabolic acidosis).
• Blood Glucose: Check frequently, especially in children and those with altered mental status (risk of neuroglycopenia).
• Renal Function Tests (Urea, Creatinine).
• Complete Blood Count (CBC), Coagulation Studies (INR) - less common acute effects.
• Urine pH: Monitor during alkaline diuresis.
• Chest X-ray: Assess for pulmonary edema.

Diagnostic criteria

Clinical presentation consistent with salicylate toxicity + History of exposure + Elevated serum salicylate level + Characteristic acid-base disturbance (especially metabolic acidosis).

Non-pharmacological management

• Stabilization: ABCDE approach. Airway management if comatose/seizing. High-flow oxygen.
• Fluid Resuscitation: Aggressive IV fluid resuscitation with isotonic crystalloids (e.g., Normal Saline, Ringer's Lactate) to correct dehydration, maintain renal perfusion, and aid elimination. Avoid fluid overload, especially if pulmonary edema suspected.
• GI Decontamination:
• - Activated Charcoal (Oral/NGT): Give ASAP (50g adult, 1g/kg child). Effective in reducing absorption.
• - Multiple-Dose Activated Charcoal (MDAC): Consider 25-50g q4h. Enhances elimination by interrupting enterohepatic/enteric recirculation. Requires protected airway and bowel sounds.
• - Gastric Lavage: May be considered if massive, life-threatening ingestion presenting within 1 hour (benefit uncertain vs risk). Salicylates delay gastric emptying, so potentially useful up to 4 hours per UCG (use cautiously).
• Cooling Measures: Tepid sponging, cooling blankets for hyperthermia.
• Avoid Intubation if Possible: Hyperventilation is compensatory; sedation/paralysis for intubation can worsen acidosis if ventilation not matched. If intubation necessary, maintain hyperventilation.
• Enhanced Elimination (Hospital/RR): Haemodialysis: Most effective method for removal. Indications: Severe poisoning (high levels >80-100 mg/dL or >7.2mmol/L), Altered mental status (coma, seizures), Pulmonary edema, Renal failure, Severe/worsening acidosis unresponsive to bicarbonate, Clinical deterioration despite supportive care.

Pharmacological treatment

• Glucose Supplementation: IV Dextrose to prevent/treat hypoglycemia and neuroglycopenia (brain may have low glucose despite normal serum levels). Add Dextrose to maintenance IV fluids.
• Urinary Alkalinization: IV Sodium Bicarbonate: CRITICAL for moderate-severe poisoning. Enhances renal salicylate excretion and helps shift salicylate out of CNS. Indications: Symptomatic patients, significant metabolic acidosis, high salicylate levels. Regimen: Initial bolus 1-2 mEq/kg IV, followed by continuous infusion (e.g., 150 mEq NaHCO3 in 1L D5W, run at 1.5-2 times maintenance fluid rate). Target: Urine pH 7.5-8.5 AND Serum pH ~7.45-7.55. Requires: Close monitoring of urine pH, serum pH (ABG/VBG), serum electrolytes (especially Potassium - supplement K+ aggressively as needed, alkalosis worsens hypokalemia). Contraindicated in severe renal failure, pulmonary/cerebral edema.
• Potassium Replacement: Correct hypokalemia aggressively (IV KCl), essential for effective alkaline diuresis.
• Seizures: Treat with Benzodiazepines (Diazepam/Lorazepam) IV. Avoid phenytoin.

Monitoring

Frequent monitoring of: Vital signs (HR, BP, RR, Temp, SpO2), Mental status (GCS), Acid-base status (serial ABG/VBG), Serum electrolytes (esp. K+), Blood glucose, Renal function, Urine output and pH, Serial salicylate levels (until clearly falling and non-toxic). Monitor for pulmonary edema.