Electrolyte Abnormalities Summary

GENERAL APPROACH

• intake:
• redistribution:
  output:
  urinary
  non-urinary
  -> upper GI
  -> mid GI
  -> lower GI
  -> other – skin, bleeding, sweat, RRT

POTASSIUM

Hyperkalaemia

• intake: oral intake, blood transfusion
• redistribution: acidosis, rhabdomyolysis, tumour lysis
• output:
  urinary – RTA type 4, renal failure, adrenal insufficiency, DM, K+ sparring diuretics

Hypokalaemia

• intake: inadequate intake
• redistribution: alkalosis, hypoMg2+, glucose infusion, periodic paralysis, beta-agonists
• output:
  urinary – steroids (ex or en), DKA, hyperaldosteronism, Cushings, RTA, diuretics
  non-urinary
  -> upper GI – vomiting
  -> mid GI – fistula
  -> lower GI – diarrhoea
  -> other – sweat, burns, bleeding, RRT

MAGNESIUM

Hypermagnasaemia

• intake: usually iatrogenic (Mg infusion)
• redistribution:
• output:
  urinary – renal failure increases risk of accumulation

Hypomagnasaemia

• intake: TPN, malabsorption, alcoholism
• redistribution: insulin, hungry bone syndrome
• output:
  urinary – RTA, diuretics, polyuria from any cause
  non-urinary
  -> upper GI – NG loss
  -> lower GI – diarrhoea

CALCIUM

Hypercalcaemia

• intake: Ca2+, vitamin A or D, hypoMg2+, hypovolaemia, TPN
• redistribution: immobilization, malignancy, hyperparathyroidism, sarcoid, lithium, adrenal insufficiency, endocrine causes (thyrotoxicosis, acromegaly, phaeo)
• output:
  urinary – thiazides

Hypocalcaemia

• intake: Ca2+, vitamin D, phenytoin (increased metabolism of vitamin D)
• redistribution: alkalosis, citrate toxicity, hyperphosphataemia, pancreatitis, tumour lysis syndrome, rhabdomyloysis, decreased bone turnover, hypoparathyroidism, drugs (bisphosphonates, PPI’s, SSRI’s, gentamicin)
• output:
  urinary – ethylene glycol, cis-platin, protamine, loop diuretics
  non-urinary – bleeding, plasmapheresis, citrate RRT

PHOSPHATE

Hyperphosphataemia

• intake:
• redistribution:
• output: urinary
  non-urinary
  -> upper GI
  -> mid GI
  -> lower GI
  -> other – skin, bleeding, sweat, RRT

Hypophosphataemia

• intake: malnutrition, phosphate binders, vitamin D, malabsorption, TPN
• redistribution: refeeding syndrome, insulin in DKA
• output:
  urinary – diuretics, osmotic diuresis, hyperparathyroidism, proximal tubular dysfunction (Fanconi’s syndrome)
  non-urinary
  -> upper GI
  -> mid GI
  -> lower GI – diarrhoea
  -> other – sweat, burns, sepsis, bleeding

SODIUM

• different to the rest!
• must think of mainly redistribution of H2O

To sort out:

(1) Osmolality
(2) Volume assessment
(3) Where is the H2O being lost from?

HYPOTONIC

Hypovolaemic

• urinary (urinary Na+ high) – diuretics, osmotic diuretics, RTA, salt wasting, mineralocorticoid deficiencies
• non-urinary (urinary Na low)
  -> upper GI – vomiting
  -> mid GI – pancreatitis, bowel obstruction
  -> lower GI – diarrhoea, bowel preparation
  -> other – skin, bleeding, sweat

Euvolaemic

-> SIADH (most common)
-> psychogenic polydipsia
-> hypotonic IVF therapy
-> adrenal insufficiency
-> hypothyroidism

Hypervolaemic

-> CHF
-> cirrhosis
-> nephrotic syndrome
-> hypothyroidism
-> pregnancy
-> TURP syndrome

ISOTONIC (pseudohyponatraemia)

• high proteins
• high lipids

HYPERTONIC

• glucose
• mannitol
• sorbitol
• radiocontrast
• advanced renal disease (need to correct osmolality = measured osmolalilty – urea)