A 6-year-old in ketoacidosis shows arterial blood gas: pH 7.22, PaCO2 28 mmHg, bicarbonate 11 mEq/L, sodium 136 mEq/L, chloride 98 mEq/L. Calculate the anion gap and identify the disturbance.
- A Anion gap 38 mEq/L: mixed respiratory and metabolic acidosis
- B Anion gap 13 mEq/L: normal anion gap metabolic acidosis
- C Anion gap 27 mEq/L: high anion gap metabolic acidosis ✓
- D Anion gap 22 mEq/L: respiratory alkalosis with metabolic compensation
Correct answer: C. Anion gap 27 mEq/L: high anion gap metabolic acidosis
Explanation
The anion gap equals sodium minus chloride minus bicarbonate: 136 minus 98 minus 11 equals 27 mEq/L, clearly elevated above the normal range of roughly 8 to 16, confirming high anion gap metabolic acidosis from accumulating ketoacids. The low PaCO2 of 28 mmHg represents appropriate respiratory compensation by Kussmaul breathing, not a separate respiratory disorder. Ignoring the gap and reading only pH and bicarbonate leads to the wrong classification of a normal gap acidosis, and option A mislabels compensatory hyperventilation.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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