Aspirin overdose commonly causes which acid-base disturbance?

• A. Respiratory alkalosis
• B. Metabolic acidosis
• C. Mixed respiratory alkalosis and metabolic acidosis
• D. Metabolic alkalosis

Answer: (C)

Aspirin overdose causes a two-pronged disruption of acid-base balance. It stimulates the respiratory center, leading to hyperventilation and a drop in carbon dioxide, which produces respiratory alkalosis. At the same time, salicylates impair cellular metabolism and increase the production of organic acids (like lactate and ketoacids), creating a high anion gap metabolic acidosis. These opposing effects can occur together, giving a mixed picture of both respiratory alkalosis and metabolic acidosis. A single disturbance—pure respiratory alkalosis or pure metabolic acidosis—doesn't capture the full, typical pattern seen with salicylate toxicity, and metabolic alkalosis is not expected. The pattern may evolve, with respiratory alkalosis more prominent early and metabolic acidosis developing or worsening as toxicity progresses.