MCQ: Vomiting | Excessive Thirst

Clinical Scenario:

A 7-year-old boy is brought to the emergency department with 8 hours of repeated vomiting, excessive thirst and progressively rapid breathing. Over the last 2 hours, he has become irritable and confused. He is dehydrated and tachycardic. There is no history of diabetes mellitus.

Laboratory investigations show:

  • Glucose: 108 mg/dL (6.0 mmol/L)
  • pH: 7.47
  • PaCO₂: 21 mmHg
  • HCO₃⁻: 15 mmol/L
  • Anion gap: 24 mmol/L
  • Serum lactate: mildly elevated
  • Urine ketones: trace

Which of the following is the most likely diagnosis?

A. Diabetic ketoacidosis
B. Ethylene glycol poisoning
C. Salicylate poisoning
D. Sepsis with lactic acidosis
E. Starvation ketoacidosis

Correct answer & Explanation:

Correct answer: C. Salicylate poisoning

Explanation

Salicylate poisoning can closely mimic diabetic ketoacidosis (DKA), with vomiting, dehydration, tachypnea, altered mental status and an increased anion gap. The key distinction is the acid–base pattern.

Salicylates directly stimulate the respiratory center, producing primary respiratory alkalosis. At the same time, they interfere with cellular metabolism and promote organic acid accumulation, producing high-anion-gap metabolic acidosis. Therefore, the combination of low PaCO₂ with low bicarbonate is an important clue to salicylate toxicity.

In this child, the normal blood glucose and only trace ketonuria make DKA unlikely. Ethylene glycol poisoning can cause high-anion-gap metabolic acidosis but does not characteristically produce this prominent respiratory alkalosis.

A suspected salicylate overdose should prompt measurement of serum salicylate concentration, serial assessment of acid–base status and electrolytes, and appropriate supportive management. Urinary alkalinization with intravenous sodium bicarbonate is an important treatment in significant salicylate poisoning.

You can also practice another MCQ on Cannabis intoxication.

References

  1. O’Malley GF, O’Malley R. Aspirin and other salicylate poisoning. Merck Manual Professional Edition. Updated April 2025.
  2. Proudfoot AT, Krenzelok EP, Vale JA. Position paper on urine alkalinization. J Toxicol Clin Toxicol. 2004;42(1):1-26. doi:10.1081/CLT-120028740.
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