Definition – What is hyperkalaemia?

Hyperkalaemia is an electrolyte abnormality with potentially life-threatening consequences. Although a universal definition does not exist, the European Resuscitation Council defines hyperkalaemia as a serum potassium (K+) level ≥5.5 mmol/L.

Hyperkalaemia is further subdivided as:

• Mild: 5.5-5.9mmol/l
• Moderate: 6.0-6.4mmol/l
• Severe: >6.5mmol/l

Aetiology

• Renal disease – acute or chronic renal impairment
• Drugs – potassium sparing diuretics, ACE inhibitors, NSAID’s, cyclosporin, heparin, suxamethonium, digoxin toxicity
• Diabetic ketoacidosis
• Metabolic acidosis
• Tissue breakdown – rhabdomyolysis, tumour lysis syndrome, severe burns
• Addison’s disease
• Type 4 renal tubular acidosis (Hyporeninaemic hypoaldosteronism)
• Exogenous potassium load e.g. infusion of potassium chloride, transfusion of stored blood

Clinical features

• Asymptomatic – usually causes no symptoms and signs until high enough to cause cardiac arrest
• Symptoms tend to be non-specific and include: nausea, vomiting, diarrhoea, chest pain, palpitations, shortness of breath, muscle weakness, paraesthesia
• ECG changes: although it is variable, there is reasonable correlation between increasing severity of hyperkalaemia and ECG changes: tall tented p waves -> prolonged PR interval -> flattened or absent p waves -> wide QRS ->sine wave pattern -> ventricular tachycardia/ventricular fibrillation/asystole

Investigations

• Hyperkalaemia is diagnosed on renal biochemistry testing
• Additional essential investigations required immediately include:
  • 12-lead ECG to identify changes as described as above
  • Arterial or venous blood gas to identify metabolic acidosis and rapidly confirm the potassium result
  • Blood glucose to rule out hyperglycaemia
• Further investigations as indicated e.g. serum cortisol, digoxin level
• Rule out spurious result due to haemolysis unless ECG changes are present requiring urgent treatment

Management

• Rule out spurious cause unless ECG changes are present requiring emergency treatment
• Mild-Moderate hyperkalaemia: dietary potassium restriction, stop any causative drugs, loop diuretic to increase potassium excretion
• Severe hyperkalaemia: K > 6.5mmol/l or > 6.0mmol/l if ECG changes is a Medical emergency:
  • 1. Stabilise cardiac potential to prevent VF or asystole – IV calcium gluconate 10ml 10% IV over 10 minutes with ECG monitoring, repeat if ECG changes persist after 5 minutes
  • 2. Move potassium into cells from the extracellular fluid – IV insulin 10 units and 50ml 50% glucose over 15-30 minutes, nebulised salbutamol 5mg, if severe acidosis consider IV 1.26% sodium bicarbonate (500ml IV over 60 minutes)
  • 3. Increase renal potassium excretion – IV diuretics to encourage renal loss of potassium
  • 4. Prevent further potassium absorption – Discontinue potassium-containing infusions and oral drugs that may be contributing, give calcium resonium orally (15g three times daily) or rectally (30g)
  • 5. Treat underlying cause
  • 6. Monitor potassium levels frequently 2-4 hourly acutely and daily thereafter
  • 7. Haemodialysis or peritoneal dialysis if conservative management fails and often the required in patients with chronic kidney disease, particularly if already on dialysis.