Non-clinical sciences/Lab medicine · Acid–base

Metabolic alkalosis

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What it means

↑pH with ↑HCO₃. Causes: vomiting/NG loss (H⁺ and Cl⁻), loop/thiazide diuretics, mineralocorticoid excess (Conn's, Cushing's), milk-alkali. Urinary chloride separates saline-responsive (low, vomiting/diuretics) from saline-resistant (high, mineralocorticoid).

Worked example

Persistent vomiting: pH 7.52, HCO₃ 36, low urinary chloride, often with hypokalaemia.

In the exam

After a week of vomiting from pyloric obstruction a patient has pH 7.52, HCO₃ 36 and a low urinary chloride.

What settles it

Metabolic alkalosis = high HCO₃ (vomiting/diuretics); respiratory alkalosis = low CO₂ (hyperventilation).

Classically confused with

Respiratory alkalosis

Source: StatPearls — Acid-base