Hypokalaemia

• Mild – 3.0-3.5
• Moderate – 2.5-3.0
• Severe – <2.5

Aetiologies

• can remember with the mnemonic Dr froM MIT:
  • Decreased $\mathrm{K}{}^{+}$ intake (e.g. poor dietary intake, starvation)
  • Hypomagnesaemia which results in increased potassium loss
  • Mineralocorticoid excess
    • Cushing syndrome
    • Primary aldosteronism
    • Renal vascular hypertension
    • Renin producing tumour
    • Adrenogenital syndrome
    • Licorice excess
    • Bartter syndrome
    • Liddle syndrome
  • Increased loss
    • Drugs (digoxin, diuretics, laxatives, liquorice, steroids, antibiotics (carbapenems, gentamicin, amphortericin B))
    • Skin - profuse sweating, extensive burns
    • GI - diarrhoea, vomiting, ileostomy, intestinal fistula, villous adenoma, laxatives
    • Renal - tubular disorders, nephrogenic DI
    • Endocrine - hyperaldosteronism, Cushing syndrome, Conn syndrome
    • Dialysis - haemodialysis on low $\mathrm{K}{}^{+}$ dialysate,peritoneal dialysis
  • Transcellular shift
    • Insulin/glucose therapy
    • Beta-agonists
    • Alkalosis: respiratory and metabolic
    • Hypokalaemic periodic paralysis

Clinical Features

• Muscles - weakness (legs > arms), cramps, ileus, rhabdomyolysis
• Cardiac conduction abnormalities
  • Dangerous arrhythmias are more common when hypokalaemia also occurs with QT prolonging drugs, digoxin toxicity, Hypomagnesaemia, coronary ischaemia

Assessment

History

• fatigue
• muscle cramps
• weakness
• constipation
• rhabdomyolysis
• ascending paralysis
• respiratory failure
• arrhythmias
• symptoms more likely in pre-existing heart disease (IHD, CHF, LVH)
• medications: cause of hypokalaemia and also anti-arrhythmics (sotalol → increased risk of arrhythmias)

Examination

Investigations

• ECG
• EUC
• CMP
• Digoxin level if on digoxin

Workup

1. Most aetiologies are evident from history
2. Assess magnesium level
3. Check acid base status and measure urine potassium excretion

Management

• Replace magnesium as fascilitates a more rapid correction of hyperkalaemia

• For patients with hypokalaemia in the setting of essential diuretic use (e.g. heart failure) or hyperaldosteronism, a potassium-sparing diuretic is usually more effective than chronic potassium replacement
• In stable patients, the maximum IV dose of potassium is 20 mmol/h
• In unstable arrhythmias or when cardiac arrest is imminent use 2 mmol/min (20mmol total) for 10 minutes followed by 10 mmol over 5-10 minutes and magnesium 10mmol over 10 minutes
• During cardiac arrest
  • Give a 5 mmol bolus, repeat as required
  • Give a 5 mmol bolus of IV magnesium sulfate, may repeat once, then 20 mmol over 4 h infusion
  • Stop precipitants: e.g. furosemide infusion, β-agonists (salbutamol), insulin without adequate $\mathrm{K}{}^{+}$ and glucose-containing fluids (drives intracellular potassium shift)
  • Aim for potassium ≥ 4.0 mmol/L before discontinuing aggressive replacement
  • Consider beta-blockade (e.g. esmolol) is an emerging adjunct for refractory VF due to adrenergically driven arrhythmia (e.g. caffeine, salbutamol, thyroid storm)

Sources

• Hypokalaemia
• Hypokalaemia • LITFL • CCC Electrolytes