“Dr., this patient X has hypokalaemia, potassium 2.5. Can I fast correct with IV KCl 2g stat?”

Introduction

• Normal range of serum potassium: 3.5 – 5.1 mmol/L
• Severity of hypokalaemia:
  • Mild: 3.1 – 3.5 mmol/L -> oral potassium supplement, then repeat RP tomorrow
  • Moderate: 2.5 – 3 mmol/L -> ECG + consider fast correction with IV KCl, then repeat serum potassium after 1 hour
    • ±IV KCl maintenance in drip / oral supplementation
  • Severe: <2.5 mmol/L -> ECG + fast correction with IV KCl, then repeat serum potassium after 1 hour
    • ±IV KCl maintenance in drip / oral supplementation

*There is no fixed rule on the treatment. Treatment must be aligned with clinical judgement.

Calculation of potassium deficit & requirement

(i) Potassium deficit

Potassium deficit (g) = [(4 – current potassium level) × 0.4 × bodyweight]/13.4]

• 1 g KCl contains 13.4 mmol potassium & 13.4 mmol chloride (as shown in the picture above)
• 1 vial = 10 mL KCl = 1 g KCl

(ii) Potassium requirement

Potassium daily requirement (g) = 1 mmol/kg/day

Example

Patient X, weight 60kg, serum potassium 2.5 mmol/L

• Deficit: [(4 – 2.5) x 0.4 x 60] / 13.4 = 2.68 g
• Daily requirement: 1 x 60 / 13.4 g = 4.47 g

• Correction of deficit: fast correct with IV KCl 2g in 200 mL NS over 2 hours
  • Repeat serum potassium post correction
• Daily requirement:
  • If the patient is on IV drip maintenance e.g. 4 pints NS / 24 hours, may add 1g KCl in each pint NS (the calculated requirement is 4.47 g per day. Hence 1g in each pint is applicable.)
  • If the patient is not on IV drip and having good oral intake, add oral potassium supplement (e.g. Tab Slow K 1.2 g TDS for 3 days), and encourage oral intake

Medications for hypokalaemia

• Intravenous – IV KCl, examples of administration:
  • IV KCl 1g in 100 mL NS over 1 hour
  • IV KCl 2g in 200 mL NS over 2 hours
• Oral:
  • Tab Slow K e.g. 1.2 g TDS
  • Mist KCl e.g. 15 mL TDS