ICU · Electrolytes

Electrolyte Disorders in Critical Illness — Sodium, Potassium, Calcium, Magnesium and Phosphate

Also known as Dysnatraemia · Hyponatraemia · Hypernatraemia · Hyperkalaemia · Hypokalaemia · Electrolyte disturbances

Electrolyte disorders are among the commonest and most immediately dangerous derangements in critical illness, and their correction is governed less by the absolute concentration than by the speed and direction of change. This topic builds the examiner's framework around the two highest-yield cations — sodium and potassium — and a concise account of calcium, magnesium and phosphate. For sodium, the central ideas are that hyponatraemia is a disorder of water handling classified by osmolality and volume status, that the dangerous consequences are cerebral oedema (acute) and osmotic demyelination (over-correction), and that the rate of correction is the single most important decision. For potassium, the central ideas are that hyperkalaemia with ECG change is an emergency treated in a fixed sequence, and that hypokalaemia is a product of redistribution or total-body deficit. The evidence base is anchored on the Adrogué NEJM reviews of dysnatraemia, the Verbalis expert-panel hyponatraemia recommendations, the Kovesdy and Palmer potassium reviews, and the Ayuk hypomagnesaemia review, with the calcium and phosphate content resting on the standard ICU texts.

Checked against its sources on 1 Sept 2026