Renal System >
Hyponatremia

Decreased levels of sodium concentration in the blood (<135mmol/L)

  • Classifications:
    • Hypovolaemic
    • Euvolemic
    • Hypervolaemic
Risk Factors
  • Modifiable:
    • Vomiting
    • Diarrhoea
    • Low dietary sodium intake
  • Non-Modifiable:
    • Increasing age
Aetiology
  • Hypovolaemic – vomiting, diarrhoea, diuretics eg Thiazide
  • Euvolemic – SIADH, drugs which stimulate ADH secretion eg chlorpropamide
  • Hypervolemic – cirrhosis, excess water intake, chronic renal failure
Pathophysiology
  • SIADH
    1. ADH secreted inappropriately
    2. Aquaporins retain water
    3. Fluid overload
    4. RAAS inactivated
    5. Decreased aldosterone
    6. Decreased sodium reabsorption
    7. Greater sodium levels in urine
  • Diarrhoea, vomiting
    1. Sodium and fluid depletion
  • Cirrhosis
    1. Reduced albumin synthesis
    2. Water and sodium movement into interstitial space
    3. Sodium levels decrease
  • Thiazide diuretic
    1. Inhibit Na/Cl cotransporter in DCT
    2. Reduced sodium reabsorption from kidneys
    3. Natriuresis
Clinical Presentation
  • Confusion
  • Nausea
  • Fatigue
  • Muscle spasms
  • Irritability
  • Restlessness
Investigations
  • Bloods:
    • Serum Osmolality
    • Urea & Electrolytes
    • LFTs
  • Imaging: n/a
  • Special:
    • Urinary Sodium & Potassium
Management
  • IV fluids: hypertonic saline
  • If euvolemic:
    • Fluid restriction
    • Complete sodium screen
  • Endocrinologist referral if the cause of hyponatremia = unclear
Complications
  • If sodium loss is rapid, a fluid shift occurs into the intracellular compartment in brain → cerebral oedema & seizures

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