Potassium disorders

High and low potassium [K]. 20 mins.

Rob Hunter, Consultant Nephrologist. Part of Renal in the Edinburgh MBChB.

Hyperkalaemia

Severe hyperkalaemia is a medical emergency because it can cause life-threatening cardiac dysrhythmia. The commonest causes are acute or chronic kidney failure and drugs inhibiting the renin-angiotensin system.
Hyperkalaemia gif by Edinburgh nephro alumnus Dr Cilien Kearns, @artibiotics

Management involves:

• stabilising cardiac conduction (with intravenous calcium salts)
• shifting potassium into cells (a temporary holding measure)
• enhancing potassium removal from the body (in the urine or using renal replacement therapy)

For mild-to-moderate hyperkalaemia, it is important to weigh the benefits of potassium-lowering therapy against the iatrogenic risks. These risks include hypoglycaemia (after insulin therapy) and decompensated heart failure (after stopping RAS inhibitors).

Hyperkalaemia video – 15 mins – covers …

Core resources

• Hyperkalaemia in hospital  UK Renal Association 1-page algorithm 2020 (pdf, 2.9Mb)
• Hyperkalaemia in primary care  UK Renal Association 1-page algorithm 2020 (pdf 0.7Mb)
• Hyperkalaemic cardiac arrest  UK Renal Association 1-page algorithm 2020 (pdf 0.4 Mb)
• Hyperkalaemia (Edren textbook)
• Low potassium diet for patients (edren.org/info)
• Case …

Hypokalaemia

Hypokalaemia may be due to shift of potassium into cells, potassium loss in the urine or loss from the gut (vomiting or diarrhoea).

• SHIFT INTO CELLS
  • catecholamines / beta-agonists
  • insulin
  • re-feeding syndrome
  • hypokalaemic periodic paralysis
  • metabolic alkalosis
• RENAL POTASSIUM LOSS
  • with metabolic alkalosis
    • vomiting, diuretics, Gitelman, Bartter, mineralocorticoid XS, apparent mineralocorticoid XS
  • with metabolic acidosis
    • renal tubular acidosis types I & II
    • DKA
  • with variable acid-base
    • Mg-depletion
    • non-reabsorbable anion (e.g. high-dose IV penicillins)
• GASTROINTESTINAL POTASSIUM LOSS
  • • with normal acid-base
      • anorexia, tea & toast diet, laxative abuse
    • with metabolic acidosis
      • diarrhoea, villous adenoma

The urine potassium concentration or 24 hr urine potassium excretion can be helpful in distinguishing between renal and extra-renal causes of hypokalaemia. Urine potassium is

• Low (< 20 mM on a spot sample or < 15 – 20 mmoles per day) in extra-renal causes
• High (> 20 mM on a spot sample or > 15 – 20 mmoles per day) in renal causes.

One important thing to remember here is that vomiting actually promotes renal potassium loss, so expect a high urine potassium concentration after vomiting.

Core resources

• Case …

Additional reading

• Electrolyte disorders, a general approach (this site)
• More advanced resources … coming