Hypokalaemia: Causes and Effects

Hypokalaemia

• Hypokalaemia is caused by potassium levels below 3.5mM.

Causes of Hypokalaemia

• Vascular issues can cause hypokalaemia.
• Infection, specifically severe diarrhoea, can induce hypokalaemia.
• Trauma, including release of urinary tract obstruction and acute myocardial infarction, can lead to hypokalaemia.
• Autoimmune conditions can result in hypokalaemia.
• Metabolic factors such as the correction of megaloblastic anaemia, dietary deficiency, and alkalosis can also cause hypokalaemia.
• Iatrogenic causes include potassium-wasting diuretics like thiazides and loop diuretics.
• Excess corticosteroid administration stimulates mineralocorticoid receptors, resulting in aldosterone-like effects and hypokalaemia.
• Nephrotoxic drugs like aminoglycosides, amphotericin B, and cytotoxic drugs can cause hypokalaemia via renal injury.
• Excessive insulin administration can lead to hypokalaemia by increasing shunting of potassium intracellularly.
• β-agonists like salbutamol can shunt potassium intracellularly, causing hypokalaemia.
• Other drugs including carbenoxolone and liquorice can induce hypokalaemia.
• Administration of IV drugs without potassium, like normal saline, may cause hypokalaemia.
• Neoplastic causes include acute leukaemia, villous adenoma, and ACTH-producing tumours.
• Degenerative causes include hepatic failure, heart failure, kidney and adrenal disease.
• Kidney and adrenal diseases such as nephrotic syndrome, Barter's syndrome, Conn's disease, renal tubular acidosis, and renal tubular damage may cause hypokalaemia.
• Syndromes such as Liddle's syndrome and Gitelman's syndrome can induce hypokalaemia.
• Pyloric stenosis can cause hypokalaemia.

Clinical Features of Hypokalaemia

• Hypokalaemia is usually asymptomatic, but symptomatic when severe (K+ <2.5mM).
• Muscle weakness is a clinical feature of hypokalaemia due to low intracellular potassium.
• Symptomatic hyponatraemia can be a clinical feature of hypokalaemia.
• Increased frequency of atrial and ventricular ectopic beats, is a feature and is more common in patients with cardiac disease.
• Increased risk of digoxin toxicity as hypokalaemia leads to increased binding of digoxin to the Na+-K+ pump.
• Interstitial renal disease can occur with chronic hypokalaemia.
• ECG changes include small T-waves with prominent U-waves, prolonged PR interval, and ST segment depression.

Management of Hypokalaemia

• Identify and treat the underlying cause as soon as possible.
• Acute hypokalaemia may spontaneously correct.
• Withdraw oral contraceptives and purgatives.
• Administer oral potassium supplements as slow-release or effervescent potassium.
• Intravenous potassium is indicated in conditions such as cardiac arrhythmias, muscle weakness, or severe diabetic ketoacidosis.
• Do not administer intravenous potassium at more than 20mmol/hour or at a concentration greater than 40mmol/minute.
• Measure and correct serum magnesium levels when hypokalaemia has not been corrected.
• In patients with poor renal function, the potassium replacement rate should be less than 2mM/hour.
• Hourly monitoring for ECG changes is necessary for patients management.
• Mix potassium ampoules with normal saline, as dextrose can worsen hypokalaemia.