Salicylate overdose

The mixed respiratory alkalosis and metabolic acidosis in a sweaty, confused patient point towards salicylate overdose. The development of pulmonary oedema suggests severe poisoning and is an indication for haemodialysis

Salicylate overdose leads to a mixed respiratory alkalosis and metabolic acidosis. Early stimulation of the respiratory center leads to a respiratory alkalosis whilst later the direct acid effects of salicylates (combined with acute renal failure) may lead to an acidosis. In children metabolic acidosis tends to predominate

Features

• hyperventilation (centrally stimulates respiration)
• tinnitus
• lethargy
• sweating, pyrexia*
• nausea/vomiting
• hyperglycaemia and hypoglycaemia
• seizures
• coma

Treatment

• general (ABC, charcoal)
• urinary alkalinization is now rarely used - it is contraindicated in cerebral and pulmonary oedema with most units now proceeding straight to haemodialysis in cases of severe poisoning
• haemodialysis

Indications for haemodialysis in salicylate overdose

• serum concentration > 700mg/L
• metabolic acidosis resistant to treatment
• acute renal failure
• pulmonary oedema
• seizures
• coma

** Salicylates cause the uncoupling of oxidative phosphorylation leading to decreased adenosine triphosphate production, increased oxygen consumption and increased carbon dioxide and heat production