Electrolyte Imbalance: Sodium and Potassium

Question 1

What are causes of Hypernataemia?

Answer 1

• Fluid loss without water replacement
• Diabetes insipidus: suspected if large volume of urine
• Osmotic diuresis
• Primary aldosteronism
• Iatrogenic

Question 2

What is the management of Hypernatraemia?

Answer 2

• Give water orally
  
  • If not glucose 5% slowly
• Use 0.9% saline IV if hypovolaemic

Question 3

What are causes of Hyponatraemia in Dehydrated patients?

Answer 3

• Na+ >20mmol/L in Urine
  
  • Addison’s Disease
  • Renal Failure
  • Diuretic Excess
  • Osmolar Diuresis (increase urea and glucose)
• Na+ <20mmol/L in Urine
  
  • Diarrhoea
  • Vomiting
  • Fistulae
  • Burns
  • Rectal villous adenoma
  • Small Bowel Obstruction
  • Trauma
  • Cystic Fibrosis
  • Heat Exposure

Question 4

What are causes of Hyponatraemia in Non-dehydrated patients?

Answer 4

• Oedematous
  
  • Nephrotic syndrome
  • Cardiac Failure
  • Liver Cirrhosis
  • Renal Failure
• Non-Oedematous
  
  • >100mmol/kg Urine Osmolality
    
    • SIADH
  • <100mmol.kg Urine Osmolality
    
    • Water Overload
    • Severe Hypothyroidism
    • Glucocorticoid insufficiency

Question 5

How is Asymptomatic Chronic Hyponatraemia managed?

Answer 5

Fluid restriction usually enough but can use Demeclocycline

Question 6

How is Symptomatic or Acute Hyponatraemia managed?

Answer 6

• Cautious rehydration with 0.9%. Look out for Central Pontine Myelinosis
• Vasopressor Receptor Antagonists
  
  • Promote water excretion without loss of electrolytes
  • Effective in treating hypervolemic or euvolemic hyponatraemia

Question 7

How is Emergency management of Hyponatraemia done?

Answer 7

Consider 1.9% saline with or without furosemide

Question 8

What are causes of SIADH?

Answer 8

• Malignancy: Lung small cell, Pancreas, Prostate, Thymus or Lymphoma
• CNS Disorder: Meningoencephalitis, Abscess, Stroke, Subarachnoid or Subdural haemorrhage, Head injury, Neurosurgery, Guillain-Barre, Vasculitis, SLE
• Chest disease: TB, Pneumonia, Abscess, Aspergillosis
• Endocrine disease: Hypothyroidism
• Drugs: Opiates, SSRIs, Cytotoxic
• Other: Trauma, Surgery, Acute intermittent porphyria

Question 9

What is the management of SIADH?

Answer 9

• Treat cause and restrict luid
• Consider Salt +/- loop diuretic if severe
• Vasopressin receptor antagonist can be used

Question 10

What are symptoms of Diabetes Insipidus?

Answer 10

• Polyuria
• Polydipsia
• Dehydration
• Symptoms of hypernatraemia

Question 11

What are causes of Diabetes Insipidus?

Answer 11

• Cranial
  
  • Idiopathic
  • Congenital: defect in ADH gene, Wolfram syndrome (DIDMOAD)
  • Tumour: craniopharyngioma, metastases, pituitary tumour
  • Trauma
  • Hypophysectomy
  • Autoimmune hypophysistis
  • Infiltration: histiocytosis, sarcoidosis
  • Vascular: sheehans syndrome
  • Infection: meningoencephalitis
• Nephrogenic
  
  • Inherited
  • Metabolic: low potassium, high calcium
  • Drugs: lithium, demeclocycline
  • Chronic Kidney Disease
  • Post-obstructive nephropathy

Question 12

What are tests for Diabetes Insipidus?

Answer 12

• U&Es
• Serum and urine osmolarities. U:P osmolarity ration is <2
• Dilutional hyponatraemia
• Diagnostic test: Water deprivation test

Question 13

What is the treatment of Diabetes Insipidus?

Answer 13

• Cranial DI
  
  • Find the cause
  • Give desmopressin
• Nephrogenic DI
  
  • Treat the cause
  • If not working, then give Bendroflumethiazide and NSAIDs