Hypokalaemia management

Definition

Hypokalaemia is defined as a plasma potassium concentration of <3.5 mmol/L.

Common clinical features include:

• Weakness

• Constipation

• Paralysis

• Bradycardia

• Reduced tendon reflexes

Investigations

Recommended investigations include:

• Point-of-care ECG

• Serum electrolytes

• Serum creatinine and urea

• Bedside ultrasound, where indicated

Additional investigations should be guided by the patient's clinical presentation.

Non-pharmacological treatment

• Perform both primary and secondary assessment and provide appropriate interventions.

• Administer oxygen if the patient is hypoxic or has increased work of breathing.

• Connect the patient to a monitor and obtain vital signs.

• Establish intravenous access.

Pharmacological management

Management depends on the severity of hypokalaemia.

Mild hypokalaemia (3.0–3.5 mmol/L)

Potassium chloride (PO)

• Adults: 20–40 mEq every 8 hours, dissolved in 100–150 mL of water.

• Children: 2 mEq/kg every 8 hours, diluted in oral fluids or food.

If hypokalaemia is associated with diarrhoea, administer:

Oral rehydration salts (ORS)

• 5 mL/kg/hour.

Moderate hypokalaemia (2.5–2.9 mmol/L)

Potassium chloride (IV)

• Adults: 10 mEq/hour.

• Children: 0.5 mEq/kg/hour.

Dilute in 25–50 mL of:

• 0.9% sodium chloride, or

• Dextrose normal saline (DNS), or

• 5% dextrose.

Administer via a peripheral vein.

Do not exceed 10 mEq/hour.

Severe hypokalaemia (<2.5 mmol/L)

Both oral and intravenous potassium replacement are recommended.

Oral replacement

Potassium chloride (PO)

• Adults: 28 mmol (K⁺) per hour, if tolerated, dissolved in 100–150 mL of water.

• Children: 2 mEq/kg every 8 hours.

OR

Intravenous replacement

Potassium chloride (IV)

• Adults: 20 mEq diluted in 100 mL of intravenous fluid and infused over 1 hour via a cubital fossa vein.

• Continue measuring serum potassium every 1–2 hours until serum potassium is >2.8 mmol/L.

• Children: 1 mEq/kg/hour.

The calculated hourly potassium dose should be multiplied by 12.5 mL to determine the dilution volume using:

• Normal saline (NS)

• Dextrose normal saline (DNS)

• 5% dextrose (D5%)

Do not exceed 10 mEq/hour.

Role of magnesium

Serum magnesium should be assessed.

If magnesium is low, administer:

Magnesium sulphate 50% (IV)

• Adults:

  • Initially administer 4 mL, diluted to 10 mL with 0.9% sodium chloride, infused over 20 minutes.

  • Follow with potassium chloride infusion.

  • Then administer magnesium sulphate 50% at 0.12 mL/kg/day.

• Children:

  • 0.1 mL/kg/dose, infused over 2 hours.

Hypokalaemia during cardiac arrest (adults)

Potassium chloride (IV)

• 10 mEq over 5 minutes.

• The dose may be repeated once if required.

Important notes

• Twenty (20) mEq of potassium increases serum potassium by approximately 0.25 mEq/L.

• Aim to replace approximately 25% of the potassium deficit within the first 6 hours.

• Potassium chloride must never be administered by intramuscular injection or intravenous push.

• Slow-K 600 mg tablet is equivalent to 8 mEq of potassium.

• Potassium chloride injection 7.5%: 1 mL = 1 mEq.

ECG changes in hypokalaemia

Typical ECG findings include:

• Increased P-wave amplitude

• Prolonged PR interval

• ST-segment depression

• QT interval prolongation

• Flattened or inverted T waves

• Prominent U waves