Salicylate poisoning - Overdose and poisoning

Salicylate poisoning

Definition

Accidental or deliberate overdose of salicylate (aspirin).

Aetiology

Ingestion of salicylates is usually accidental in toddlers; it is now rare as paracetamol and ibuprofen have become the household analgesic and antipyretic agents of choice. Deliberate self-harm with aspirin is also unusual.

Pathophysiology

Salicylates have a direct effect on the central respiratory drive increasing both the rate and depth of ventilation. This hyperventilation leads to respiratory alkalosis, which is compensated for by renal excretion of bicarbonate and potassium. Salicylates also uncouple oxidative phosphorylation in skeletal muscle with consequent accumulation of pyruvic, lactic and acetoacetic acids. The combination of the metabolic and renal effects result in a metabolic acidosis. The increase in metabolic rate can lead to hyperpyrexia and the antiplatelet effects of salicylate increases the risk of bleeding.

Clinical features

Patients may appear asymptomatic even in the presence of significant overdose. In moderate overdose patients may present with deep respiratory movements and tinnitus as early signs, and later with, deafness, hyperpyrexia, vasodilation and tachycardia. In severe overdose disorders of consciousness occur progressing to coma especially in children.

Complications

Cerebral oedema and pulmonary oedema, which may be exacerbated by forced diuresis.

Investigations

Blood glucose, blood gases, U&Es, prothrombin time and bicarbonate levels should be measured. Treatment is based on plasma salicylate levels (>500 mg/L (3.6 mmol/L) in adults, >300 mg/L (2.2 mmol/L) in children) taken 2 hours in symptomatic patients and 4 hours in asymptomatic patients following ingestion.

Management

Activated charcoal may be considered in conscious patients within 1 hour of ingestion and consumption above 120 mg/kg. Patients may require protection of the airway, correction of hypoglycaemia and hypokalaemia, and then any metabolic acidosis with intravenous sodium bicarbonate.

Haemodialysis is used if plasma salicylate level is 700 mg/L (5.1 mmol/L), renal or cardiac failure, convulsions or if there is severe metabolic acidosis.