Hypokalaemia

Question 1

Define mild, moderate and severe hypokalaemia

Answer 1

Mild 3.1-3.5mmol/l
Moderate 2.5 - 3.0mmol/l
Severe <2.5mmol/l

Question 2

What are causes of hypokalaemia?

Answer 2

Medication:
Diuretics - thiazide and loop diuretics that cause excess K loss
Steroids
Excessive insulin
Beta-2 agonists such as salbutamol

Excess loss:
Diarrhoea and vomiting - bowel obstruction, fistular formation, pyloric stenosis, laxative abuse
Hyperaldosteronism (Conn's syndrome)
Burns
Excessive sweating

Decreased intake:
Inadequate replacement in IV fluids while NBM
Malnutrition

Misc:
Chronic alcoholism
Cushing's syndorme
Renal tubular acidosis
Hypomagnesaemia
Chronic peritoneal dialysis

Question 3

How does hypokalaemia present?

Answer 3

Generally asymptomatic
Severe cases: muscle weakness, paraesthesia, constipation, ileus, pseudo-obstruction, hypotonia, hyporeflexia, muscle cramps, tetany, resp failure, cardiac arrhythmias

Question 4

What are ECG changes in hypokalaemia?

Answer 4

Causes cardiac excitability resulting in re-entry loops

Elongated PR interval
T wave flattening (T wave inversion)
Prominent U wave
ST depression

Can develop into VT or VF

Question 5

How should patients be investigated?

Answer 5

ECG checking for cardiac involvement - if there is, cardiac monitoring and aggressive replacement

Bloods: FBC, U&E, Ca, PO4, Mg - magnesium deficiency exacerbates K wasting by increasing K secretion

VBG for immediate potassium check

Question 6

Management of hypokalaemia?

Answer 6

Treat underlying cause and replace potassium
Mild cases without cardiac involvement - oral supplements as replacement should suffice

Moderate/severe hypokalaemia, ongoing losses, unable to take supplements orally, cardiac involvement:
IV replacement

Daily bloods should be performed and hypomagnesaemia should be corrected

Dextrose free solution should be given to minimise insulin stimulation and causing a worsening hypokalaemia.