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Potassium - Hypokalaemia


Hypokalaemia is defined as a serum potassium of < 3.5mmol/L

Can be further subclassified as per below:

MILD – 3.0-3.5mmol/L

MODERATE – 2.5-3.0mmol/L

SEVERE <2.5mmol/L

Hypokalaemia generally leads to hypomagnesaemia, so it is important to measure and replace Mg2+ as required.

Hypokalaemia mechanism


Increased urine loss

Diuretic drugs
Amphotericin B

Increased gastrointestinal loss

Diarrhoea and vomiting
Laxative over use

Reduced potassium intake

Poor nutrition


Secondary (accelerated hypertension, renal artery stenosis)
Apparent mineralocorticoid excess (genetic licorice)
Congenital adrenal hyperplasia

Shift of potassium into cells

Metabolic alkalosis

Anabolic state
Hypokalaemia periodic paralysis

Insulin overdose
Insulin for severe metabolic derangement (DKA)

Beta adrenergic drugs

(Adapted from eTG hypokalaemia table 5.21)


History and examination

  • Can be asymptomatic
  • Weakness, lethargy, paralysis, tetany
  • Cardiac dysrhythmias if severe: VT, VF, heart block, asystole



EUC, CMP, Albumin

ECG done early on suspicion of electrolyte abnormalities:

  • T wave flattening/inversion (earliest sign)
  • Increased P wave amplitude
  • Prolongation of PR interval
  • Widespread ST depression
  • Prominent U waves (Best seen in the precordial leads V2-V3)
  • Apparent long QT interval due to fusion of T and U waves (= long QU interval)


Cardiac monitoring and treatment of cause are the underlying principles. The rate of replacement and methods are highly dependent on the symptoms and signs and degree of deficit.

MILD Hypokalaemia (3-3.5mmol/L)

Oral is usually best but can lead to GI upset

  • ORAL (eg slowK): potassium chloride sustained release 1200 to 3600mg (16-48mmol) daily in divided doses


  • Effervescent (eg chlorvescent): Potassium 548 to 1096mg (14-28mmol) dissolved in water and taken orally, 2 to 3 times daily.

MODERATE TO SEVERE Hypokalaemia (2.5- 3.0mmol/L and asymptomatic)

Replace as per mild if can take oral

Consider IV replacement as for severe – if unable to take oral, associated with symptoms muscle paralysis or cardiac rhythm disturbance with ECG evidence of hypokalaemia

MODERATE TO SEVERE Hypokalaemia (<3.0mmol/L and symptomatic)

Potassium chloride 20 to 40mmol/L IV according to premixed infusion bag:

  • Peripheral access: 20mmol KCl in 1L 0.9% sodium chloride over 2hrs
  • Central access: 20mmol KCL in 0.9% sodium chloride over 1 hour

Rapid intravenous administration or overdose may cause cardiac arrest.

Rate of infusion through a peripheral IV line should not exceed 10mmol/hour

Rate of infusion through a central line should not exceed 40mmol/hour

Refer to critical care for higher rates

Cardiac monitoring whilst infusing and serum potassium concentration measured every 2 hours

Concurrent oral can be used if conscious

If magnesium low (<0.8mmol/L) give MgSO4 2.5g (10mmol) over 4hrs IV

Once the hypokalaemia is no longer severe, the rate of intravenous potassium repletion should be reduced or changed to oral therapy. Patients should be treated until the serum potassium concentration is persistently above 3.0 to 3.5 mmol/L and symptoms or signs attributable to hypokalaemia have resolved

Consider consultation with critical care when

Severe hypokalaemia requiring iv replacement



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