Salicylate Toxicity Acid-Base — RACP Adult Medicine MCQ

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ModerateClinical PharmacologySalicylate Toxicity Acid-BaseRACP Adult Medicine

A 35-year-old woman presents with dyspnoea and bilateral crackles. ABG shows pH 7.52, PaCO₂ 20 mmHg, PaO₂ 65 mmHg, HCO₃ 16 mmol/L. Serum salicylate level is 4.5 mmol/L (toxic). What is the characteristic acid-base pattern of salicylate toxicity?

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Correct answer: B — Mixed respiratory alkalosis AND metabolic acidosis

Salicylate toxicity produces a characteristic mixed acid-base disturbance: respiratory alkalosis (direct stimulation of the medullary respiratory centre causes hyperventilation → low PaCO₂) AND a high anion gap metabolic acidosis (salicylate impairs oxidative phosphorylation, generating lactate and ketoacids, plus salicylate itself is an unmeasured anion). The respiratory alkalosis typically predominates early; as toxicity progresses, the metabolic acidosis worsens. Treatment includes IV sodium bicarbonate (to alkalinise urine and enhance renal salicylate excretion) and haemodialysis for severe toxicity.

Reference: eTG – 2025 – Toxicology