Hyperkalaemia: Causes and Mechanisms

• Hyperkalaemia occurs when serum potassium levels exceed 5.2mM.
• It results from either excessive potassium release from cells or impaired excretion.

Causes of Hyperkalaemia

• Vascular causes include transfusion of stored blood and massive blood transfusions.
• Some patients have familial pseudo-hyperkalaemia, which is inherited.
• Trauma such as acute kidney injury is a common cause.
• Rhabdomyolysis and tissue necrosis lead to potassium release and hyperkalaemia.
• Excessive exercise can also cause hyperkalaemia.
• Hyperkalaemia can be caused by autoimmune diseases.
• Metabolic disorders like acidosis and diabetic ketoacidosis can cause hyperkalaemia.
• Iatrogenic causes include medications; potassium-sparing drugs (amiloride, spironolactone), ACE inhibitors, NSAIDs, heparin, and cyclosporine.
• Neoplasms like tumour lysis, leukaemia and infectious mononucleosis can cause hyperkalaemia
• Degenerative diseases such as Addison's and Gordon's syndrome can cause hyperkalaemia.

Clinical Features

• A serum potassium level above 7mM is a medical emergency.
• Concerning signs include a fast irregular pulse, chest pain, palpitations, and light-headedness.
• Muscle weakness is a sign of hyperkalaemia.
• Associated with acidosis is Kussmaul respiration.
• Decreased cardiac excitability leads to eventual asystole (cardiac arrest).
• Hypotension and bradycardia occur.
• ECG changes include tall tented T-waves, reduced P-wave, widened QRS complex, and a sine-wave pattern just before cardiac arrest; also, ventricular fibrillation.

Treatment

• Management of severe hyperkalaemia includes ECG monitoring and IV access.
• Protect the myocardium with 10ml of 10% calcium gluconate solution over 5 minutes to protect the myocardium from sudden arrest, repeat after 15 minutes if needed.
• Drive potassium into cells using insulin 10IU with 50ml of 50% glucose over 10-15 minutes: monitor blood glucose and potassium regularly.
• Alternatively, administer salbutamol intravenously at 0.5mg in 100ml of 5% dextrose over 15 minutes or nebulize it; this method is rarely used.
• For severe acidosis (<6.9), infuse 1.26% sodium bicarbonate instead of the hypertonic type.
• Deplete body potassium over 24 hours using polystyrene sulfonate resins to bind potassium in the gut via ion fluxes.
• Using up to 15g 3-times daily along with laxatives or 30g followed by an enema removes it.
• Haemodialysis or peritoneal dialysis is used if previous measures fail; at this point, hyperkalaemia is considered refractory and is common among end-stage kidney disease (ESKD) patients.