A key concept for the exam is to understand that salicylate overdose leads to a mixed respiratory alkalosis and metabolic acidosis. Early stimulation of the respiratory centre 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*
  • (salicylates cause the uncoupling of oxidative phosphorylation leading to decreased adenosine triphosphate production, increased oxygen consumption and increased carbon dioxide and heat production)
• nausea/vomiting
• hyperglycaemia and hypoglycaemia
• seizures
• coma

Treatment

• general (ABC, charcoal)
• urinary alkalinization with intravenous sodium bicarbonate - enhances elimination of aspirin in the urine
• haemodialysis

Indications for haemodialysis in salicylate overdose

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