HYPOKALAEMIA
(serum K⁺ <3.5 mmol/L)

Symptoms and signs

• Often none, or neuromuscular symptoms (e.g. muscle weakness, absent reflexes, ileus)

Investigations

Immediate

• ECG changes – depressed ST, flat T, U waves, arrhythmias (arrhythmias may cause cardiorespiratory symptoms)

Helpful

• Repeat K⁺ (U&E). Take sample from arm without a drip
• Venous HCO₃^– – when raised (metabolic alkalosis) indicates chronic depletion; if <22 mmol/L in absence of GI loss, suspect renal tubular acidosis – refer to renal team
• Urine K⁺ if cause not obvious
• Serum magnesium (Mg²⁺) for persistent urine K⁺ loss especially patients with diarrhoea or on diuretics

Common Causes

• Blood taken from drip arm (artefact)
• Any excessive gastrointestinal fluid loss
• Renal loss: urine K⁺ >20 mmol/L – diuretics, mineralocorticoid excess (hyperaldosteronism and excess cortisol), Mg²⁺ deficiency see Hypomagnesaemia guideline, and renal tubular disease
• Intracellular shift (redistribution): insulin or bicarbonate treatment, theophylline, beta₂ agonists, periodic paralysis, rapid blood cell proliferation
• Intravenous fluid therapy, with inadequate electrolyte replacement

• Manage K⁺. For guidance follow flowchart
• If K+ given IV, monitor serum potassium concentration at least daily
• Treat the underlying cause. If cause not obvious, refer to renal or endocrine team for further evaluation