Hyperkalaemia

• Hyperkalaemia is defined as plasma potassium ≥ 5.5 mmol/L
• Severe hyperkalaemia is >6.5 mmol/L
• Severe hyperkalaemia is a medical emergency due to the risk of life-threatening arrhythmias. Hyperkalaemia is one of the reversible causes of cardiac arrest. Prompt treatment is vital, especially in patients who have ECG changes
• Renal causes of hyperkalaemia:

  • Kidneys are responsible for 90% of potassium excretion
  • AKI
  • CKD
• Iatrogenic causes of hyperkalaemia:

  • ACE inhibitors e.g. Ramipril
  • ARBs e.g. candesartan
  • Potassium sparing diuretics e.g. spironolactone
  • Digoxin
  • NSAIDs
  • Trimethoprim
  • Potassium supplements
• Tissue damage sustained secondary to trauma or burns results in the release of significant volumes of potassium from damaged cells
• In diabetic ketoacidosis (DKA), potassium shifts from the intracellular to the extracellular space due to a lack of insulin, resulting in hyperkalaemia
• Aldosterone promotes the excretion of potassium by the kidneys.

  In Addison’s disease, the adrenal glands cannot produce adequate aldosterone levels, which results in reduced renal excretion of potassium
• Pseudohyperkalaemia can occur for a wide variety of reasons, including:

  • Haemolysis (e.g. prolonged tourniquet time, prolonged sample transport time, use of incorrect blood bottles)
  • Blood sample being taken from a limb receiving IV fluids containing potassium
  • Leukocytosis and thrombocytosis
• Signs and symptoms of hyperkalaemia:

  • Typically vague - general weakness and fatigue
  • Palpitations
  • Chest pain
  • SOB
  • Depressed or absent tendon reflexes
• Bedside investigations:

  • 12 lead ECG - identify any ECG changes
  • Blood gas - rapidly check serum potassium and exclude DKA
  • Capillary blood glucose - exclude hyperglycaemia/DKA
• ECG changes in hyperkalaemia:

  • early sign - tall tented T waves
  • Prolonged PR interval
  • Flattened P waves
  • Wide QRS complexes
  • Sine wave pattern - late sign
  • Arrhythmias - usually bradycardia due to hyperkalaemia induced AV block
• Laboratory investigations:

  • U&Es - repeat sample should be sent
  • FBC - exclude haemolysis
  • Cortisol - exclude Addison's disease (cortisol would be low)
  • Digoxin - to exclude toxicity in patients taking digoxin
• A potassium level of ≥6.5 mmol/L and/or a hyperkalaemia-associated ECG changes requires urgent treatment
• There are 4 components to the management of severe hyperkalaemia:

  • Prevent further accumulation of potassium
  • Stabilise the cardiac membrane (if ECG changes present)
  • Shift potassium intracellularly (reduce serum potassium)
  • Remove potassium from the body
• Preventing further accumulation of potassium:

  • Stop any IV fluids containing potassium
  • Suspend any medication that can increase serum potassium
  • Suspend any potassium supplements
• Stabilising the cardiac membrane if ECG changes present:

  • IV calcium
  • 10ml 10% calcium chloride
  • 30ml 10% calcium gluconate
  • Stabilises the myocardium temporarily for 30-60 minutes
  • Does not reduce serum potassium levels
• Shifting potassium intracellularly:

  • Insulin-glucose infusion: insulin shifts potassium from the extracellular to the intracellular compartment. Glucose helps maintain capillary blood glucose levels.
  • Salbutamol: promotes the movement of potassium into cells
• Removing potassium from the body:

  • Calcium polystyrene sulfonate resin - can remove potassium via the GI tract but this is slow and causes constipation
  • Correction of the underlying cause - kidneys should then resume their normal function of excreting adequate volumes of potassium via the urine
  • Haemodialysis - last resort if patient failed to respond to other therapies
• Rhabdomyolysis is another cause of hyperkalaemia