An 18-month-old with 3 days of profuse watery diarrhoea shows ABG values: pH 7.24, PaCO2 34 mmHg, bicarbonate 13 mEq/L, sodium 135 mEq/L, potassium 3.4 mEq/L, chloride 113 mEq/L. What type of acid-base disturbance is present?

• A High anion gap metabolic acidosis due to lactic acid accumulation
• B Respiratory acidosis with inadequate renal compensation
• C Metabolic alkalosis with compensatory hypoventilation
• D Normal anion gap metabolic acidosis due to fecal bicarbonate loss ✓

Explanation

The anion gap is 135 minus 113 minus 13, which equals about 9 mEq/L, well within the normal range of 8 to 12. Diarrhoea causes direct loss of bicarbonate in stool with retention of chloride, giving a hyperchloremic, normal anion gap metabolic acidosis. Option A would require a large unmeasured anion such as lactate, which would widen the gap above 12, and the chloride here is high rather than low, excluding alkalosis.

Reference: Nelson Textbook of Pediatrics, 22nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.