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Low and high potassium: ECG watch, IV potassium safety and the patients at risk

  • Assessment

Too much or too little potassium can stop the heart: the nurse knows who is at risk, watches the rhythm and never gives IV potassium as a push.

Updated

What it is

Potassium is the main electrolyte inside cells and is essential for the heart, nerves and muscles. The kidneys remove the excess, so kidney failure, some blood pressure medicines, supplements and salt substitutes can raise it; vomiting, diarrhoea, diuretics, laxatives and low magnesium can lower it. Both extremes can cause dangerous arrhythmias and cardiac arrest, often with few warning symptoms. The nurse identifies patients at risk, follows the results, watches the heart rhythm, gives potassium and the other treatments exactly as ordered and per protocol, and treats IV potassium as a high-alert medicine.

Reference values

  • Serum potassium reference range: about 3.5 to 5.1 mEq/L (MedlinePlus, Open RN); use your laboratory's range.
  • High potassium: kidney failure, ACE inhibitors, angiotensin receptor blockers, mineralocorticoid antagonists, supplements, salt substitutes, burns, crush injury, haemolysis, acidosis.
  • Low potassium: diuretics, vomiting, diarrhoea, laxative overuse, low magnesium, insulin, eating disorders.
  • Replacement and treatment amounts: according to the order and the institutional protocol.

What you need

  • Cardiac monitor or 12-lead ECG as ordered.
  • Infusion pump.
  • Latest potassium, kidney function, magnesium and glucose results.

How to measure it (and why)

  1. Identify patients at risk (kidney disease, diuretics, vomiting or diarrhoea, potassium supplements) — they need closer result checks.
  2. Read each potassium result against the range and the trend, and report abnormal values — symptoms may come late.
  3. Ask about palpitations, weakness, cramps and tingling and check the pulse — they are the bedside clues.
  4. Start cardiac monitoring or get an ECG as ordered — both extremes cause arrhythmias.
  5. Before replacing potassium, review kidney function and urine output with the order — failing kidneys retain potassium.
  6. Give IV potassium only diluted, by infusion pump, at the ordered rate, never as a push — a bolus can stop the heart.
  7. Apply the institution's high-alert medicine checks to IV potassium — an error can be fatal.
  8. When insulin with glucose is given to lower potassium, check glucose as often as the protocol requires — hypoglycaemia is a risk.
  9. Recheck potassium when ordered and record the result and the response — it shows whether treatment worked.
  10. Teach diet and medicine changes as ordered, including avoiding salt substitutes if potassium is high — they contain potassium.

How to read it

  • High potassium with ECG changes is an emergency: treatment may include IV calcium to protect the heart, insulin with glucose, potassium binders or dialysis, as ordered.
  • A large drop in potassium can cause abnormal heart rhythms, especially in people with heart disease.
  • Low magnesium is one of the causes of low potassium, so magnesium is checked as well.
  • Very low potassium can cause life-threatening paralysis.

Next step: when to call for help

  • Call for any potassium result outside the range, especially a new or rising one.
  • Call at once for an arrhythmia or ECG change, palpitations, chest pain, a slow or irregular pulse or fainting.
  • Call for new muscle weakness, difficulty breathing or paralysis.
  • Stop and check if an IV potassium infusion is running faster than ordered, and call.
  • Collapse or no pulse: call for help and start resuscitation.

Test yourself

Think of the answer, then tap the question to see it.

Why is IV potassium never given as an IV push?

Because a bolus can stop the heart; it is given diluted, by infusion pump, at the ordered rate and per protocol.

Which patients are at risk of high potassium?

Those with kidney failure, on ACE inhibitors, ARBs or mineralocorticoid antagonists, on supplements or salt substitutes, or after burns or crush injury.

What does the nurse check when insulin with glucose is given to lower potassium?

Blood glucose, as often as the protocol requires, because hypoglycaemia is a risk.

Why is the heart rhythm monitored in potassium imbalance?

Because both high and low potassium can cause dangerous arrhythmias and cardiac arrest, often with few symptoms.

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Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order.

Sources: Nursing Fundamentals (Open RN), 15.4 Electrolytes (Open RN, Wisconsin Technical College System (CC BY 4.0), LibreTexts, 2021); Nursing Fundamentals (Open RN), 15.6 Applying the Nursing Process (Fluids and Electrolytes) (Open RN, Wisconsin Technical College System (CC BY 4.0), LibreTexts, 2021); High potassium level, MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Low blood potassium, MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).

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