Hyperkalaemia

Plasma potassium levels are regulated by a number of factors including aldosterone, acid-base balance and insulin levels. Metabolic acidosis is associated with hyperkalaemia as hydrogen and potassium ions compete with each other for exchange with sodium ions across cell membranes and in the distal tubule.

Causes of hyperkalaemia:

• acute kidney injury
• drugs*: potassium sparing diuretics, ACE inhibitors, angiotensin 2 receptor blockers, spironolactone, ciclosporin, heparin**
• metabolic acidosis
• Addison's disease
• rhabdomyolysis
• massive blood transfusion

Foods that are high in potassium:

• salt substitutes (i.e. Contain potassium rather than sodium)
• bananas, oranges, kiwi fruit, avocado, spinach, tomatoes

*beta-blockers interfere with potassium transport into cells and can potentially cause hyperkalaemia in renal failure patients - remember beta-agonists, e.g. Salbutamol, are sometimes used as emergency treatment

**both unfractionated and low-molecular weight heparin can cause hyperkalaemia. This is thought to be caused by inhibition of aldosterone secretion

The "K-BANK" Mnemonic • K – K-sparing Diuretics: Spironolactone, Eplerenone, Amiloride, Triamterene. • B – Beta-blockers: These interfere with the Na+/K+-ATPase pump, preventing potassium from entering cells. • A – ACE Inhibitors & ARBs: (Ramipril, Lisinopril, Losartan). These are the most common culprits in clinical practice because they suppress aldosterone. • N – NSAIDs: Drugs like Ibuprofen and Naproxen inhibit prostaglandin synthesis, which in turn reduces renin and aldosterone secretion. • K – Known Others: * Heparin: (As discussed earlier, it inhibits aldosterone). ◦ Digoxin: (In acute toxicity, it blocks the Na+/K+ pump). ◦ Trimethoprim: (A very common "hidden" cause; it acts like the diuretic Amiloride). ◦ Ciclosporin/Tacrolimus: (Calcineurin inhibitors).

The "Hidden" Exam Trap: Trimethoprim The examiners love to give you a patient with a stable chronic kidney disease (CKD) who is started on antibiotics for a UTI and suddenly develops a potassium of 6.2mmol/L. • The Culprit: Trimethoprim. • The Mechanism: It blocks the epithelial sodium channels (ENaC) in the distal tubule, exactly like the diuretic Amiloride.

ECG changes