Hypokalaemia

From Ganfyd

Severe Hypokalaemia [K+] < 2.5 mmol/l should be treated urgently. Hypokalaemia exacerbates digoxin toxicity. Consult local guidelines on precise emergency management.

Potassium is the major intracellular cation.

• Hypokalaemia is regarded as a plasma [K⁺] < 3.5 mmol/l
• Severe hypokalaemia is regarded as a plasma [K⁺] < 2.5 mmol/l and should be treated urgently.
• Hypokalaemia can be as arrhythmogenic as hyperkalaemia.

Comprehensive review in ^[1]

Clinical

Symptoms

Symptoms can be non-specific and can be unrecognised.

• Asymptomatic
• Weakness
• Lethargy
• Reduced tone
• Tetany
• Depression

Investigations

Plasma [K⁺] < 3.5 mmol/l

Hypokalaemia/hypokalaemia ECG will show changes

• U waves
• Reduced amplitude T waves

Causes

• Reduced dietary intake (e.g. following surgery, ileus, obstruction)
• Redistribution (e.g. respiratory alkalosis, insulin)
• GI loss
  • Vomiting and Diarrhoea
  • Bowel obstruction
  • Mucus secreting villous adenoma
• Renal loss
  • K⁺ losing diuretics
  • Conn's syndrome
  • Cushing's syndrome
  • Osmotic losses in diabetic ketoacidosis

Treatment

Urgency depends on clinical symptoms, the K⁺ level and the patient. Approach is to:

• Eliminate cause
• Replace Potassium, either i.v. or oral as appropriate
• Patient may also have a low Magnesium. K+ level will not rise until [Mg] levels has been normalised.

Practical Points

Enough potassium must be given to meet both basal requirements (~1mmol/kg/day) and deficit. As a rough guide, every 1 mmol below the normal range corresponds to a deficiency of 100-200mmol K⁺.

1. Oral
   • Sando-K = 12mmol K⁺ per tablet
   • Kloref = 6.7mmol K⁺ per tablet
   • Various fruits contain potassium and may be preferrable to the above.^[2]
2. IV therapy
   • through standard fluid bags (usu max. 40mmol per bag)
   • on the general ward, max. 10mmol per hour
   • if central line and cardiac monitoring available, up to 10-20mmol/hour, though such rapid replacement is rarely required.

References