A 17-year-old is brought in having ingested an unknown quantity of aspirin tablets. He has tinnitus and hyperventilation. Which blood gas pattern is classically expected early on?
Answer and explanation
Correct answer: D. Respiratory alkalosis, then metabolic acidosis with a raised anion gap
- Step 1: Salicylates stimulate the respiratory centre and uncouple oxidative phosphorylation.
- Step 2: Early hyperventilation gives respiratory alkalosis, followed by high anion gap metabolic acidosis as toxicity progresses.
Answer
Respiratory alkalosis, then metabolic acidosis with a raised anion gap.
Why not the others: Metabolic alkalosis with hypokalaemia from vomiting: Metabolic alkalosis does not describe salicylate toxicity. Isolated respiratory acidosis with a normal anion gap: Respiratory acidosis is not the early pattern. Normal blood gas until the next day: Blood gases are abnormal early.
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