A 5-year-old with salicylate poisoning has arterial blood gas: pH 7.50, PaCO2 26, HCO3 20, and plasma salicylate level 65 mg/dL. Urine is being alkalinized. Which acid-base pattern is characteristic of moderate-to-severe salicylate toxicity in this age group?

• A Pure high-anion-gap metabolic acidosis
• B Mixed respiratory alkalosis and high-anion-gap metabolic acidosis ✓
• C Pure respiratory alkalosis
• D Normal anion gap metabolic acidosis with compensatory respiratory alkalosis

Explanation

Salicylate toxicity produces a characteristic mixed acid-base disturbance. Salicylate directly stimulates the respiratory center causing primary respiratory alkalosis (low PaCO2). Simultaneously, salicylate uncouples oxidative phosphorylation, generates organic acids (salicylic acid, ketoacids, lactic acid), and causes high-anion-gap metabolic acidosis. In this child pH 7.50, low PaCO2 (26) and low-normal HCO3 (20) indicate a mixed picture — the respiratory alkalosis is currently dominant. This mixed pattern is specific to salicylate toxicity and contrasts with pure respiratory alkalosis (mild toxicity) or pure metabolic acidosis (severe, late-stage poisoning).

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.