See also

Basic Paediatric ECG interpretation
Dehydration
Diabetic ketoacidosis (DKA)
Electrolyte abnormalities 
Hyperkalaemia
Intravenous fluids

Key points

1. The oral/enteral route is preferred for potassium administration
2. Intravenous potassium is a high-risk medication and carries risks of inadvertent hyperkalaemia, fluid overload, and peripheral vein extravasation and thrombophlebitis. Rapid intravenous administration or overdose may cause cardiac arrhythmia or arrest 
3. Monitor fluid status and electrolytes in all children receiving potassium replacement. Children with an initial serum potassium <3.0 mmol/L should have cardiac monitoring, as should those receiving IV replacement
4. Specialist advice should be sought for critical (K <2.0 mmol/L) or symptomatic hypokalaemia

Background

Hypokalaemia is defined as a plasma potassium level less than 3.5 mmol/L

• In normal acid-base status, a 1 mmol/L decrease in serum potassium concentration represents a whole-body deficit of at least 200 mmol. Concurrent metabolic acidosis may falsely elevate the serum potassium and lead to an underestimation of total body deficit. Metabolic alkalosis can have the opposite effect
• Hypokalaemia is commonly associated with hypomagnesaemia. Serum magnesium should be measured and replaced as required

Causes of hypokalaemia

Prevention

In general, children eating a variety of foods will meet their daily potassium requirements (approximately 2-4 mmol/kg/day)

Consider maintenance fluids containing potassium (see Intravenous fluids) for children who are

• Nil by mouth and not receiving enteral fluids for prolonged periods, particularly if associated with increased losses
• At risk of hypokalaemia, see table above for causes

Assessment

History

• Hypokalaemia is often asymptomatic
• Symptoms of hypokalaemia are more likely when serum levels rapidly decrease to below 3 mmol/L
• Skeletal muscle weakness, paralysis (in severe cases)
• Smooth muscle weakness: ileus, constipation, nausea, vomiting
• Lethargy
• Fatigue
• Confusion
• Polyuria, usually if prolonged hypokalaemia
• Features of underlying cause
• Acute diarrhoea/vomiting
• Decreased intake
• Use of medications such as salbutamol, diuretics, laxatives
• History of hypoaldosteronism

Examination

• Tachycardia, bradycardia, arrhythmia
• Fluid status (see Dehydration)
• Decreased muscle strength, hypotonia and decreased deep tissue reflexes

Management

Investigations

• Repeat potassium to verify initial result
• Serum potassium level can be falsely elevated in haemolysed/finger prick samples. A venous sample should be taken if clinical suspicion of hypokalaemia
• Urea, creatinine and electrolytes
• BGL
• Venous blood gas
• Magnesium, especially if hypokalaemia is refractory to treatment (hypomagnesaemia promotes potassium wasting) 
• ECG: if signs/symptoms of hypokalaemia, risk of cardiac arrhythmia, or serum potassium <3 mmol/L. See Basic Paediatric ECG interpretation
  • Decreased T wave amplitude (usually earliest manifestation)
  • Increased P wave amplitude
  • T wave changes (flattening, inversion)
  • ST changes (usually depression)
  • Appearance of U wave
  • QT prolongation
  • Ventricular ectopic beats
  • Arrhythmia

Treatment

Goals of treating hypokalaemia are to

• Prevent life threatening complications: arrhythmias, paralysis, rhabdomyolysis, diaphragmatic weakness
• Replace potassium deficit
• Identify and treat reversible causes, address underlying conditions

Replacement

Ensure child is passing urine before commencing potassium replacement

Potassium replacement is indicated if

• Serum potassium <3.0 mmol/L

      or

• Serum potassium <3.5 mmol/L with symptoms, signs and/or ECG changes

In mild hypokalaemia (serum levels 3.0-3.5 mmol/L), optimal treatment depends on clinical situation. Consider:

• No acute treatment, monitor electrolytes
• Increasing maintenance potassium dose
• Replacing orally/IV if anticipated ongoing losses or inadequate intake

In children with stable haemodynamics and no ECG changes, aim for a gradual correction over 24-48 hours

Measure and correct serum magnesium as necessary

Route of administration

The oral/enteral route is preferred

• Potassium is well absorbed from the gastrointestinal tract
• It is best taken with or soon after food to reduce gastrointestinal irritation

Intravenous potassium replacement should be considered in

• a child who is unable to tolerate enteral medication
• an initial serum potassium <2.5 mmol/L
• presence of ECG changes

Oral/enteral dosing

Dosage

Medication forms

For acute oral potassium replacement, consider repeat serum potassium level at a time interval guided by the clinical context and the expected serum potassium rise 

Intravenous dosing

Dosage

• Rapid intravenous administration or overdose may cause fatal cardiac arrhythmia or arrest. Administer via an infusion pump using Dose Error Reduction Software (DERS) where available. Note that concentrated potassium solutions should only be administered in critical care settings
• Include all sources of potassium when calculating replacement doses and infusion rates, eg additives to maintenance fluids, parenteral nutrition, oral/enteral supplements
• Potassium-containing fluids, including parenteral nutrition, may need to be paused during acute replacement to ensure the maximum rate of potassium administration is not exceeded

Acute intravenous potassium replacement dose

Maintenance dose (if required):

• 1-4 mmol/kg/day (max 10 mmol/hour)
• Doses greater than 4 mmol/kg/day should be discussed with a senior clinician or local retrieval service

Administration

Only administer potassium chloride IV by infusion. Never flush after potassium chloride infusions

Monitoring

Ensure regular monitoring of:

• vital signs
• clinical and fluid status including urine output
• any signs of hyperkalaemia (see Hyperkalaemia)
• IV site for phlebitis or Extravasation

Consider consultation with local paediatric team when

• Child requires admission
• Child requires potassium replacement  

Consider transfer when

• Serum potassium <2.0 mmol/L
• Symptomatic hypokalaemia especially paralysis
• Significant ECG changes such as arrhythmia, ventricular or supraventricular ectopic beats, ST changes, T wave inversion
• Renal impairment, including oliguria or high/rising creatinine
• Risk of arrhythmia
• Fluid overload
• Neonates
• Child with complex medical condition

For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services

Consider discharge when

• Asymptomatic
• Potassium >3.0 mmol/L and stable
• Fluid losses replaced and ongoing replacement possible
• Plan for ongoing monitoring (ie repeat levels) in place

Additional information

ECG: ST depression, T wave inversion, prominent U waves

Last updated October 2024