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CDHB

Aspirin (and other salicylates)

• Acute poisoning: classical symptoms of vomiting, tinnitus, hyperventilation (initial respiratory alkalosis) followed by metabolic acidosis. Severe toxicity may result in coma and seizures.
• Chronic poisoning (over 12 hours) has a higher morbidity and mortality - no GI effects, often profound dehydration, acidosis, CNS depression, ARDS, coagulopathy. (The progressive acidosis increases the volume of distribution of aspirin and high tissue level of salicylates can occur despite relatively low plasma levels).
• Risk assessment:
  • Approx 150 mg/kg causes vomiting.
  • 150-300 mg/kg mild/moderate toxicity.
  • >300 mg/kg moderate/severe toxicity.
  • >500 mg/kg potentially lethal.
• Blood concentration - nomogram helpful in acute poisoning only. Measure serum salicylate concentration at 6 hours or more post ingestion. Nomogram may dangerously under-estimate toxicity in chronic poisoning if previous salicylate taken within 24 hours, if taken over a prolonged period, or if enteric coated aspirin taken.
• Venous or arterial blood gas. An abnormal pH may be a better indication of toxicity than salicylate levels, particularly if the time since ingestion is uncertain.

Salicylate Toxicity

Salicylate Toxicity

Note: Salicylates are present in a number of over the counter preparations, e.g., methyl salicylate in oil of Wintergreen.

Treatment

• If 6 hours post ingestion, concentration low and symptoms absent then patient may be discharged after appropriate psychiatric intervention.
• Consider activated charcoal if less than 1-2 hours post-ingestion and >150 mg/kg of aspirin has been taken. Admit for observation. Monitor salicylate levels and pH between 8-12 hours to detect delayed toxicity. Charcoal can be repeated if levels continue to rise after 4 hours.
• IV fluids - all patients with significant salicylate poisoning are dehydrated.
• Check blood glucose, Na, K, creatinine, INR and APTT.
• If metabolic acidosis is present or if significant symptoms, then alkalinize urine - sodium bicarbonate 1 mmol/kg boluses IV until pH greater than 7.5, then 1000 mL of 5% glucose, plus 100 mmol of sodium bicarbonate + 40 mmol potassium chloride and the rate adjusted according to regular measurements of pH, potassium, sodium and hydration to maintain an alkaline urinary pH.

  Note: Urine output - aim for 2-3 mL/kg/hr. pH, and serum potassium need to be monitored closely (every 1-2 hours).

• If salicylate level greater than 5 mmol/L or if very unwell, then consider haemodialysis (contact Nephrologist on call). Transfer to ICU.

Topic Code: 1593