Hypokalaemia

Introduction

Hypokalaemia is a condition where there is a low Potassium level in the plasma. It is a plasma potassium less than 3.5 millimoles per Litre. Normal plasma potassium level is any value between 3.5-5 millimoles per litre.
Hypokalaemia is the most common electrolyte abnormality in hospitalised patients; mostly caused by drugs and GI disease.

Causes

Things mostly associated with increase in potassium loss

Increased renal loss:

  • Diuretics and salt-waste and secondary hyperaldosteronism
  • Increased distal delivery of non reabsorbable anions (vomiting, DKA, renal tubular acidosis)
  • Amphotericin B
  • Cushing’s syndrome,
  • Bartter’s syndrome

Increased non-renal loss:

  • GIT loss (diarrhoea, integumentary sweat)
  • Redistribution into cells: Metabolic alkalosis
  • Drugs:
    • Insulin
    • β-adrenergic agonists
    • α-adrenergic antagonists
  • Decreased intake: Starvation

Clinical features

Vary between patients and depend on the level of potassium loss
Serum K<3mmoles/Litre:

  • Fatigue
  • Myalgia
  • Weakness of the lower extremities

More severe hypokalaemia results in

  • Progressive weakness
  • Hypoventilation
  • Complete paralysis
  • ECG changes are due to ventricular depolarisation
  • Flattening/inversion of the T wave
  • Aprominent Uwave
  • ST segment depression
  • Prolonged QT interval
  • Severe depletion results in prolonged PR interval
  • Decreased voltage and widening of the QRS complex

Investigations

  • Electrocardiography
  • Electrolytes, Urea and Creatinine
  • Acid-base status
  • Identifying the underlying disease

Treatment objectives

  • Correction of potassium deficit
  • Minimize/stop on-going loss

Drug treatment

Oral route preferred)
Potassium chloride

  • Doses depend on deficits, on-going losses and renal status

Intravenous potassium (given in an infusion)

  • Do not exceed 20 mmoles/L
  • Add daily requirement of potassium and correct over 3 days

Calculation of potassium requirement

  • = Deficit × body weight (kg) × 0.4

Caution

  • Oral potassium supplements should be
    taken in an erect position or sitting upright and with plenty of water to avoid
    oesophageal erosions