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 
Symptoms can be non-specific and can be unrecognised.
- Reduced tone
Plasma [K+] < 3.5 mmol/l
Hypokalaemia/hypokalaemia ECG will show changes
- U waves
- Reduced amplitude T waves
- Reduced dietary intake (e.g. following surgery, ileus, obstruction)
- Redistribution (e.g. respiratory alkalosis, insulin)
- GI loss
- Renal loss
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.
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+.
- Sando-K = 12mmol K+ per tablet
- Kloref = 6.7mmol K+ per tablet
- Various fruits contain potassium and may be preferrable to the above.
- 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.