Potassium
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The Basics

  • 98% is intracellular
  • Serum range 3.5 – 5 mmol/L
  • K+ and H+ tend to vary together
  • Most body secretion is in urine – from distal tubules

Shifts K+ INSIDE cells

  • Insulin
  • Aldosterone
  • β-adrenergic stimulation
  • Alkalosis

Shifts K+ OUTSIDE cells

  • Addison’s disease
  • β-blockade
  • Acidosis
  • Cell lysis

Hypokalaemia

ΔΔ

  • Usually due to Excess Losses
  1. GI losses
    1. Diarrhoea
    2. Vomiting
  2. Renal losses
    1. Diuretics
    2. Excess mineralocorticoids
  3. Intracellular shift
    1. β2– adrenergic stimulation
    2. Insulin
    3. Alkalosis

Signs  & Symptoms

  1. Muscular dysfunction
    1. Weakness
    2. Cramping
    3. Fasciculation
    4. Tetany
  2. ECG changes
    1. T wave depression
    2. ST sagging
    3. U wave prominence
    4. Prolonged P-R interval

Management

  • Correct any potential cause e.g. diuretics
  • Mild   – Oral K+ supplements
    • routine K+ replacement is not needed in most patients on diuretics
  • Severe – Cautious IV K+
    • Must be:      < 20mmol/h and < 40 mmol/L

Hyperkalaemia

ΔΔ

  1. Renal
    1. Oliguric renal failure
    2. K+ sparing diuretics
  2. Metabolic acidosis
  3. Adrenal Insufficiency – e.g. Addison’s
  4. Drugs
    1. ACE-inhibitors
    2. B- blockers
    3. NSAIDS
    4. Iatrogenic K+
  5. Rhabdomyolysis
  6. Artefact – Haemolysis

Signs & Symptoms

  1. ECG changes
    1. Tall Tented T waves (TTT)
    2. Small P waves
    3. Wide QRS complexes
    4. Ventricular Fibrillation!!!
  2. Weakness
    1. Occasional paralysis
    2. Usually death first

Management

  • Correct any potential cause e.g. beta-blockers
  • If mild simply reduce intake
K+ > 6.5 mmol/L OR ECG changes   –>     URGENT TREATMENT
  1. Calcium Gluconate (10ml-10%)
    1. IV over 2 mins
    2. Repeat as necessary (stabilises the heart)
  2. Insulin & Glucose IV
    1. Drives K+ into cells
  1. Nebulised Salbutamol
  1. Polystyrene sulfonate resin (trade name- Calcium resonium)
    1. Orally or enema if N&V
  1. Dialysis?

References

  1. Guyton & Hall. Textbook of Medical Physiology
  2. The Merck manual
  3. Oxford Handbook of Clinical medicine.
  4. Patient.co.uk

References

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) currently works as a GP Registrar and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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