28/04/2013 by admin | Renal

Abnormalities of serum sodium are closely linked to water balance (excess losses vs excess administration).


  1. Serum sodium <130mmol/L
  2. p/c: asymptomatic, confusion, coma, convulsions.
  3. Types of hyponatraemia:
    1. o Hypovolaemia (‘dry’): with Na deficit. Renal losses (=diuretics, Addison’s, salt-losing nephropathy). Extra-renal losses (=vomiting, diarrhoea, burns, sweating).
    2. o Normovolaemia: with no change in Na but modest increase in water. Inappropriate IV fluids, hypothyroid, SIADH, SCA, carbamazepine, chlorpropamide.
    3. o Hypervolaemia (‘wet’): with increased Na. Renal failure, HF, liver failure, nephrotic syndrome, excess saline.
  4. Causes:
  5. SIADH: quite common, need to exclude adrenal/thyroid/pituitary/renal insufficiency/diuretics/euvolaemia.
    1. o Excess ADH = inappropriate urinary concentration.
    2. o Diagnostic criteria:
    3. Decreased osmolality (<270mosmol/kg H2O)
    4. Inappropriately concentrated urine (>100mosmol/kh H2O)
    5. Euvolaemia
    6. Elevated urinary Na
    7. No adrenal/thyroid/pituitary/renal insufficiency/diuretic use.
    8. o Usually caused by carcinomas (lung), pneumonias, CNS disorders (=meningitis/head trauma/drugs).
    9. o Mx of SIADH: correct cause, fluid restrict, demeclocycline (inhibits action of ADH).
  6. Heart Failure
  7. Iatrogenic over-vigorous IV dextrose in post-op pts
  8. Iatrogenic Addison’s disease (over-rapid corticosteroid withdrawel in elderly on large doses of steroids).
  9. Mx:
    1. o Correct cause
    2. o If hypovolaemic (p/c = thrist, tachycardia, reduced turgor, postural hypotension) – give sodium chloride IV
    3. o If hyponatraemic but not dehydrated (normovolaemic) = restrict fluid intake.
    4. o If hypervolaemic (p/c: raised JVP, oedema, HTN) – give diuretics, and fluid restrict.
  10. Complication:
    1. o Sudden correction of Na may = ‘central pontine myelinolysis’ (=encephalopathy, CN palsies, quadriplegia).
    2. o In chronic cases of hyponatraemia correct Na less than 0.5mmol/L per h.


  1. Serum sodium >145mmol/L
  2. Causes:
    1. o Hypovol: renal loss (=diuretics, post obstruction, osmotic diuresis), extra-renal loss (=sweating, burns, diarrhoea, fistula).
    2. o Normovol: renal loss (=diabetes insipidus, impaired thrist), extra-renal loss (=insensible loss from skin, respiratory tract)
    3. o Hypervol: sodium gains (=hypertonic NaCl, hypertonic dialysis, Cushing’s syndrome, hyperaldosteronsism).


  1. Again classify if patient is hypovol, normovol, or hypervol.
  2. Again, assessment of fluid status and dertermination of urinary sodium is essential in accurate diagnosis.
  3. Mx:
    1. o Identification of cause and cautious correction is indiacted.
    2. o Correct fluid deficit with physiological saline
    3. o If hypervolaemic hypernatraemic excess sodium requires removal with diuretics.
    4. o If euvolaemic hypernatraemic – give water IV as 5% dextrose. 
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