Hypokalaemia

“A low serum potassium of <3.5mmol/L”

Risk Factors

• Eating Disorders
• AIDS
• Alcoholism
• Bariatric Surgery

Aetiology

• Increased Potassium uptake
• Increased Potassium excretion
• Decreased Potassium intake
• Increased Potassium shift from extracellular to intracellular

Pathophysiology

• Increased Potassium Excretion (loss)
  • Drugs – diuretics (thiazides, loop), laxatives, glucocorticoids, fludrocortisone, penicillin, amphotericin, aminoglycosides
  • GI losses – diarrhoea, vomiting, ileostomy, intestinal fistula
  • Renal – renal tubular acidosis, diuretics, increased mineralocorticoid activity, polyuria, dialysis
  • Endocrine disorders – hyperaldosteronism, Cushing’s syndrome
• Increased Potassium Uptake
  • Insulin/glucose therapy
  • Increase in beta-adrenergic activity e.g. salbutamol, theophylline, head injury
  • Metabolic alkalosis
  • Hypothermia
  • Increased blood cell production
  • Toxins
• Decreased Potassium Intake
  • Diet
• Increased sweat loss – Magnesium depletion associated with increased renal potassium loss

Clinical Presentation

• Most patients asymptomatic and symptoms are non-specific (muscular/cardiac)
• Nervous system – cells are unable to become depolarised due to increased RMP (flaccid paralysis, weakness, muscle cramps)
• Constipation
• Respiratory difficulties

Investigations

• Bloods:
  • Urea and Electrolytes – Creatinine ratio
  • Potassium Levels – Check multiple values
• Imaging: n/a
• Special:
  • Urinary Potassium
    • To establish urinary loss vs transcellular shift
    • >30mmol = inability of kidney to concentrate potassium
  • ECG
    • ST segment depression
    • T wave flattering
    • U waves

Management

• Mild Hypokalaemia
  • Potassium supplements
  • Potassium-sparing diuretics (Spironolactone)
• Severe Hypokalaemia
  • Oral and IV KCl administration with normal saline at 10mmol/hr

Complications

• Cardiac Arrhythmias
• Rhabdomyolysis
• Ascending Paralysis