Hypokalaemia

Electrolyte Disorders > Potassium Disorders

(Electrolyte Disorders

Potassium Disorders

Hypokalaemia)

Definition and key points

Hypokalaemia: serum potassium < 3.5 mmol/L.
Common and potentially life‑threatening in the emergency department.
Causes neuromuscular dysfunction (weakness, ileus, paralysis) and cardiac electrical instability.
Priorities: prompt recognition, 12‑lead ECG, appropriate potassium replacement, and assessment/correction of magnesium (which commonly coexists and prevents effective repletion) (NICE ESUOM; Resuscitation Council UK).

Pathophysiology and causes

Mechanisms: either total body potassium loss (most common) or transcellular shifts of potassium into cells.
Excessive losses:
Renal: loop and thiazide diuretics, mineralocorticoid excess, inherited tubular disorders (Bartter/Gitelman), dialysis.
Gastrointestinal: vomiting, diarrhoea, nasogastric suction, ileostomy, secretory tumours (eg, villous adenoma).
Transcellular shift:
Insulin (therapeutic or rebound), β2‑agonists (eg, nebulised salbutamol), alkalosis, catecholamine surge, theophylline/caffeine, hypokalaemic periodic paralysis.
Inadequate intake or iatrogenic under‑replacement (eg, insufficient IV K+ in parenteral fluids).

Magnesium deficiency commonly coexists and promotes renal potassium wasting and impairs repletion-check and correct magnesium concurrently.

Clinical features and ECG

Severity and symptoms

Mild (3.0-3.5 mmol/L): often asymptomatic or nonspecific fatigue.
Moderate (2.5-2.9 mmol/L): muscle cramps, weakness, constipation, ileus, polyuria/polydipsia, palpitations.
Severe (<2.5 mmol/L): profound weakness, ascending flaccid paralysis, respiratory muscle involvement, rhabdomyolysis, ileus/pseudo‑obstruction (eg, Ogilvie’s), and high risk of ventricular arrhythmias (VT/VF), especially post‑MI.

ECG features

Obtain a 12‑lead ECG early in any patient with clinically significant hypokalaemia or suspected electrolyte‑related arrhythmia (Resuscitation Council UK).
Typical progressive ECG changes:

Ready to master this topic for the FRCEM?

Join 500+ Emergency Medicine registrars preparing with FlyteX.