Hyperkalaemia

Question 1

What is it?

Answer 1

Hyperkalaemia is a high serum potassium. It is important to remember the investigations and management of hyperkalaemia as it is a common exam and real-life scenario. The main complication is cardiac arrhythmias such as ventricular fibrillation. These can be fatal.

Question 2

Causes?

Answer 2

Conditions

Acute kidney injury
Chronic kidney disease
Rhabdomyolysis
Adrenal insufficiency
Tumour lysis syndrome

Medications

Aldosterone antagonists (spironolactone and eplerenone)
ACE inhibitors
Angiotensin II receptor blockers
NSAIDs
Potassium supplements

Question 3

Investigations?

Answer 3

Urea and Electrolytes
Hyperkalaemia is diagnosed on a formal urea and electrolytes (U&E) blood test.

Pay attention to creatinine, urea and eGFR. Acute or chronic renal failure is important as they will need discussion with the renal team and consideration of haemodialysis.

Haemolysis (breakdown of red blood cells) during sampling can result in a falsely elevated potassium. The lab might indicate that they have noticed some haemolysis and require a repeat sample to confirm the correct potassium result.

ECG Signs
An ECG is required in all patients with a potassium above 6 mmol/L. It is worth memorising the ECG changes in hyperkalaemia:

Tall peaked T waves
Flattening or absence of P waves
Broad QRS complexes

Question 4

Management?

Answer 4

Follow the local policy and protocol for treating hyperkalaemia. Get help from an experienced doctor. Patients with significant hyperkalaemia will need close ECG monitoring to detect changes and arrhythmias. Patients with significant renal impairment should be discussed with the renal physicians.

Patients with a potassium ≤ 6 mmol/L with otherwise stable renal function don’t need urgent treatment and may just require a change in diet and medications (i.e. stopping their spironolactone or ACE inhibitor).

Patients with a potassium ≥ 6 mmol/L and ECG changes need urgent treatment.

Patients with a potassium ≥ 6.5 mmol/L regardless of the ECG need urgent treatment.

The mainstay of treatment is with an insulin and dextrose infusion and IV calcium gluconate:

Insulin (e.g. actrapid 10 units) and dextrose (e.g. 50mls of 50%) drives carbohydrates into cells and takes potassium with it, reducing the blood potassium.
Calcium gluconate stabilises the cardiac muscle cells and reduces the risk of arrhythmias.

Other options for lowering the serum potassium:

Nebulised salbutamol temporarily drives potassium into cells.
IV fluids can be used to increase urine output, which encourages potassium loss from the kidneys (but don’t fluid overload patients with renal failure).
Oral calcium resonium draws potassium out of the gut and into the stools. It works slowly and is suitable for milder cases of hyperkalaemia.
Sodium bicarbonate (IV or oral) may be considered on the advice of a renal specialist in acidotic patients with renal failure. It drives potassium into cells as the acidosis is corrected.
Dialysis may be required in severe or persistent cases associated with renal failure.