The Purple Book

Hypokalaemia

Definitions

• Mild 3.1 – 3.5 mmol/L
• Moderate 2.5 – 3.0 mmol/L
• Severe <2.5 mmol/L

Causes

• Gastrointestinal loss of potassium:
  • Diarrhoea, vomiting
  • Laxative use
• Increased renal loss of potassium:
  • Diuretic treatment
  • Hypomagnesaemia
  • Mineralocorticoid excess
  • Exogenous mineralocorticoid excess (eg. steroids, liquorice, RTA type I,II)
  • Increased urine flow (osmotic diuresis)
• Drugs:
  • Loop or thiazide diuretics
  • Laxatives
  • Insulin
  • Steroids
  • Beta-agonists (e.g. salbutamol)
  • Xanthines (e.g. theophylline)

Symptoms

• Often asymptomatic
• Symptoms include:
  • Muscle cramps/pain with rhabdomyolysis
  • Weakness and fatigue
  • Palpitation and syncope
  • Cardiac arrhythmias
  • Delirium / hallucinations

Tests

• Bloods: U&E and Magnesium
• If clinical concerns: TFTs
• If muscle pains: CK
• ECG if available and potassium <3mmol/L

Management

Identify and treat the underlying cause

• Magnesium
  • Hypomagnesaemia and hypokalaemia commonly co-exist.
  • Rx of hypokalaemia unlikely to be successful without the correction of hypomagnesaemia

• Oral potassium supplements*
• Oral supplementation is well absorbed, but large doses limited by nausea and vomiting
• Mild: Sando-K (12mmol each) – 1 tablet three times a day
• Moderate: sando-K 2 tablets three times a day
• Prescribe for a max of 3 days then review
• Other K+ supplements only after discussion with renal

Provide advice on potassium rich foods e.g bananas, apricots, dark chocolate
For longer term management of recurrent hypokalaemia discuss with medical team