In metabolic acidosis caused by inorganic (mineral) acids such as HCl, serum potassium rises by approximately how much for each 0.1 unit fall in arterial pH?

• A 0.1 mEq/L
• B 0.6 mEq/L ✓
• C 1.5 mEq/L
• D 3.0 mEq/L

Explanation

Extracellular H+ enters cells in exchange for K+, so in mineral acidosis serum potassium rises roughly 0.6 mEq/L per 0.1 pH fall. In organic acidoses such as lactic acidosis and ketoacidosis, the organic anion crosses cell membranes with the proton, so the transcellular shift and hence the potassium rise are much smaller. This distinction explains why DKA patients may be total-body potassium depleted yet present with normal or high serum potassium.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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