SALICYLATES (ASPIRIN) Poisoning

SALICYLATES (ASPIRIN) Poisoning

SALICYLATES (ASPIRIN)

Salicylate ingestion at doses greater than 150, 250 and 500 mg aspirin/kg body weight produces mild, moderate and severe poisoning respectively. Salicylate poisoning can also occur with ingestion of oil of wintergreen or when salicylic ointment (e.g. verruca remover) is applied extensively to skin. Aspirin overdose commonly produces nausea, vomiting, tinnitus and deafness. Direct stimulation of the respiratory centre produces hyperventilation. Peripheral vasodilatation with bounding pulses and profuse sweating occurs in moderately severe poisoning. Petechiae and subconjunctival haemorrhages can occur due to reduced platelet aggregation but this is self-limiting. Signs of serious salicylate poisoning include metabolic acidosis, renal failure and central nervous system (CNS) effects such as agitation, confusion, coma and fits. Rarely, pulmonary and cerebral oedema occur. Death can occur as a consequence of CNS depression and cardiovascular collapse. The development of a metabolic acidosis is a bad prognostic sign, because acidosis results in increased salicylate transfer across the blood-brain barrier.

It is important to measure a plasma salicylate concentration in all but the most trivial overdose. This is best undertaken at 6 hours or later after ingestion because of continued absorption of the drug. The salicylate concentration needs to be interpreted in conjunction with the clinical features and acid-base status of the patient. Any significant metabolic acidosis should be treated with intravenous sodium bicarbonate (8.4%), and the volume given titrated to give an arterial H+ of 32-40 (pH of 7.4-7.5). Patients are often very dehydrated, and fluid loss from vomiting and sweating must be replaced, although injudicious use of intravenous fluids may precipitate pulmonary oedema. The use of multiple doses of activated charcoal (p. 207) in salicylate poisoning is controversial, but this approach is currently recommended until the salicylate concentration has peaked. Urinary alkalinisation (Fig. 9.2) is indicated for adult patients with salicylate concentrations of 600-800 mg/l. Haemodialysis is very effective at removing salicylate and correcting acid-base and fluid balance abnormalities and should be considered when serum concentrations are above 800 mg/l in adult patients and above 700 mg/l in the elderly. Other indications for haemodialysis in acute salicylate overdose are metabolic acidosis resistant to correction, severe CNS effects such as coma or convulsions, pulmonary oedema and acute renal failure.

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