Potassium

Original article by Tom Heaton | Last updated on 2/6/2014
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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