Chloride-Responsive Metabolic Alkalosis — RACP Adult Medicine MCQ

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ModerateNephrologyChloride-Responsive Metabolic AlkalosisRACP Adult Medicine

A 55-year-old man with a nasogastric tube on continuous suction after bowel surgery develops metabolic alkalosis (pH 7.52, HCO₃⁻ 38 mmol/L). Na⁺ 138, K⁺ 2.8, Cl⁻ 88 mmol/L. Urine chloride is <15 mmol/L. What is the most likely cause?

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Correct answer: D — NG suction/vomiting (chloride-responsive)

Metabolic alkalosis with low urine chloride (<20 mmol/L) is chloride-responsive — caused by loss of HCl from NG suction or vomiting. Volume contraction stimulates aldosterone, perpetuating bicarbonate retention and potassium wasting. Treatment: IV normal saline (chloride replacement) + KCl replacement. The urine chloride distinguishes responsive (<20) from resistant (>20) metabolic alkalosis.

Reference: eTG – 2024 – Acid-Base Disorders; KDIGO 2024