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Potassium disorders: hyperkalaemia and hypokalaemia
In hyperkalaemia the order is fixed — protect the heart (calcium), move potassium into the cells (insulin plus glucose, or salbutamol) and remove it from the body; in hypokalaemia look for the source of the loss and always correct magnesium too.
Why it matters in the exam
Potassium questions appear in almost every exam, usually with an ECG tracing. In hyperkalaemia the candidate must recognise peaked T waves, a long PR interval, loss of the P wave and a wide QRS, and choose the first step: when the ECG is abnormal, the first step is intravenous calcium — it does not lower potassium but stabilises the myocardial membrane. Then insulin with glucose, and then removal (loop diuretics, potassium binders, dialysis). Further questions deal with drugs that raise potassium (ACEi, ARB, MRA, trimethoprim, heparin) and with pseudohyperkalaemia from haemolysis of the sample.
Hypokalaemia shows U waves, flat T waves and ST depression, with muscle weakness. Questions test the cause: diuretics, vomiting (through alkalosis and urinary loss), diarrhoea, hyperaldosteronism (hypertension with hypokalaemia), and shift into cells after insulin. The candidate should know that a low urine potassium points to a loss outside the kidney and a high one to a renal loss, and that hypokalaemia will not correct while a magnesium deficit remains. Rate limit: through a peripheral vein usually no more than 10 mmol per hour.
Key points
- Hyperkalaemia on the ECG: peaked T, long PR, wide QRS.
- Order of treatment: calcium gluconate 10% 30 mL, insulin 10 units with glucose 25 g, then removal.
- Dialysis when the hyperkalaemia is refractory or in severe kidney failure.
- Hypokalaemia: U waves, and always correct magnesium.
- Intravenous through a peripheral vein: usually up to 10 mmol per hour.
Summary table
| Situation | Signs / ECG | Treatment | Note |
|---|---|---|---|
| Hyperkalaemia with ECG changes | Peaked T, long PR, wide QRS | Calcium gluconate 10% 30 mL intravenously | Stabilises the heart, does not lower potassium; may be repeated |
| Shift into cells | Potassium 6.0 or more | Insulin 10 units + glucose 25 g; nebulised salbutamol 10–20 mg | Monitor glucose for hours afterwards |
| Removal from the body | After stabilisation | Furosemide, sodium zirconium cyclosilicate or patiromer, dialysis | Dialysis if refractory or in severe kidney failure |
| Hypokalaemia | U waves, flat T, weakness | Oral KCl; intravenous up to 10 mmol per hour in a peripheral vein | Correct magnesium |
| Urine potassium | Low: gut loss; high: renal loss | Check blood pressure and acid-base | Hypertension + hypokalaemia → think of aldosterone |
A free exam question
מה הממצא האפשרי שסביר ביותר שיימצא בבדיקת דם בחולים שמקבלי ם את התרופות הבאות ליתר לחץ דם? (the question as examined, in Hebrew)
- א. Ramipril – Metabolic acidosis
- ב. Doxazocin – Hyperkalemia
- ג. Hydralazine – Anti Histone
- ד. Bisoprolol – Hyperphosphatemia
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Sources
- UK Kidney Association Clinical Practice Guideline: Treatment of Acute Hyperkalaemia in Adults, 2023 — Emergency treatment: cardiac protection, shifting and removal of potassium
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Fluid and Electrolyte Disturbances: Potassium
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.