A patient with a history of renal problems generalised weakness, palpitations and chest pain. His serum potassium levels are measured and come back at 8.2 mmol/L. An ECG is performed, and it shows some very alarming changes.

1. What is the definition of hyperkalaemia?
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Hyperkalaemia is defined as a plasma potassium greater than 5.5 mmol/L.

2. List 5 non-drug related causes of hyperkalaemia.
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The non-drug causes of hyperkalaemia include:

  • Renal failure
  • Excess potassium supplementation
  • Addison’s disease (adrenal insufficiency)
  • Congenital adrenal hyperplasia
  • Renal tubular acidosis (type 4)
  • Rhabdomyolysis
  • Burns and trauma
  • Tumour lysis syndrome
  • Acidosis
3. List 5 drugs that can cause hyperkalaemia.
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Drugs that can cause hyperkalaemia include:

  • ACE inhibitors
  • Angiotensin receptor blockers
  • NSAIDs
  • Beta-blockers
  • Digoxin
  • Suxamethonium
4. What are the main clinical features of hyperkalaemia?
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The clinical features of hyperkalaemia are highly variable and can be very non-specific. They include:

  • Weakness and fatigue
  • Bradycardia (due to heart block)
  • Palpitations
  • Chest pain
  • Shortness of breath
  • Tachypnoea (due to respiratory muscle weakness)
  • Muscle weakness
  • Flaccid paralysis
  • Depressed or absent tendon reflexes
5. What ECG changes are associated with hyperkalaemia?
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Hyperkalaemia is associated with very distinctive ECG changes that progressively change as the K+ level increases:

  • K+ >5.5 mmol/l – peaked T waves (usually earliest sign of hyperkalaemia), repolarisation abnormalities
  • K+ >6.5 mmol/l – P waves widen and flatten, PR segment lengthens, P waves eventually disappear
  • K+ >7.0 mmol/l – Prolonged QRS interval and bizarre QRS morphology, conduction blocks (bundle branch blocks, fascicular blocks), sinus bradycardia or slow AF, development of a sine wave appearance (a pre-terminal rhythm)
  • K+ >9.0 mmol/l – Cardiac arrest due to asystole, VF or PEA with bizarre, wide complex rhythm.

 

ECG showing features of hyperkalaemia, including narrow-based, peaked T-waves and prolonged QT interval, image sourced from Wikipedia
Courtesy of Jason E. Roediger CC BY-SA 3.0

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