Hypokalaemia

OVERVIEW

• the most common electrolyte abnormality in hospitalised patients
• mostly caused by drugs and GI disease
• most abundant cation on the body
• 2% of total body K+ is found in the extracellular space
• K+ homeostatsis largely regulated by the kidney (90% of daily K+ loss)
• rest eliminated via GI tract
• normal K+ = 3.5-5.0mmol/L

SEVERITY

• MILD – 3.0-3.5
• MODERATE – 2.5-3.0
• SEVERE
  -> upper GI – vomiting
  -> mid GI – fistula
  -> lower GI – diarrhoea
  -> other – sweat, burns, bleeding, RRT

ALL CAUSES (Dr from MIT)

Decreased K+ Intake – poor dietary intake, starvation,

Magnesium depletion -> increases renal potassium loss – poor diet, increased Mg2+ loss

Mineralocorticoid excess

• primary aldosteronism
• Cushing’s syndrome
• accelerated hypertension
• renal vascular hypertension
• renin producing tumour
• adrenogenital syndrome
• licorice excess
• Bartter syndrome
• Liddle syndrome

Increased Loss

• Drugs – 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, various syndromes
• Endocrine – hyperaldosteronism, Cushing’s disease, Conn’s syndrome
• Dialysis – haemodialysis on low K+ dialysate, peritoneal dialysis

Transcellular Shift

• insulin/glucose therapy
• beta-agonists
• alkalosis: respiratory and metabolic
• hypokalaemic periodic paralysis

HISTORY

• mild: no symptoms
• 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

• CVS: instability, arrhythmias
• NEURO: weakness, sensation

INVESTIGATIONS

• quantify severity and find cause
• K⁺
• Mg²⁺
• Ca²⁺, phosphate
• ECG: on seen in severe hypokalaemia, U waves, T wave flattening, ST depression -> VT/VF, long QT and Torsades
• digoxin level -> particularly at risk if become hypokalaemic

MANAGEMENT

• replace Mg2+ as facilitates a more rapid correction of hypokalaemia
• non-acute situation – 10-20mmol/hr
• life threatening arrhythmia:
  -> K+ 20mol over 10 min
  -> Mg2+ 10mmol over 10 min

References and Links

LITFL

• CCC – Hyperkalaemia management
• CCC – Hyperkalaemia DDx
• CCC – Hypokalaemia
• CCC – Hypokalaemia Mind Map
• ECG Library – Hyperkalaemia
• ECG Library – Hypokalaemia
• Clinical Case – Hyperkalaemia
• CCC – Potassium