Abnormalities of serum sodium are closely linked to water balance (excess losses vs excess administration).
- Serum sodium <130mmol/L
- p/c: asymptomatic, confusion, coma, convulsions.
- Types of hyponatraemia:
- o Hypovolaemia (‘dry’): with Na deficit. Renal losses (=diuretics, Addison’s, salt-losing nephropathy). Extra-renal losses (=vomiting, diarrhoea, burns, sweating).
- o Normovolaemia: with no change in Na but modest increase in water. Inappropriate IV fluids, hypothyroid, SIADH, SCA, carbamazepine, chlorpropamide.
- o Hypervolaemia (‘wet’): with increased Na. Renal failure, HF, liver failure, nephrotic syndrome, excess saline.
- SIADH: quite common, need to exclude adrenal/thyroid/pituitary/renal insufficiency/diuretics/euvolaemia.
- o Excess ADH = inappropriate urinary concentration.
- o Diagnostic criteria:
- Decreased osmolality (<270mosmol/kg H2O)
- Inappropriately concentrated urine (>100mosmol/kh H2O)
- Elevated urinary Na
- No adrenal/thyroid/pituitary/renal insufficiency/diuretic use.
- o Usually caused by carcinomas (lung), pneumonias, CNS disorders (=meningitis/head trauma/drugs).
- o Mx of SIADH: correct cause, fluid restrict, demeclocycline (inhibits action of ADH).
- Heart Failure
- Iatrogenic over-vigorous IV dextrose in post-op pts
- Iatrogenic Addison’s disease (over-rapid corticosteroid withdrawel in elderly on large doses of steroids).
- o Correct cause
- o If hypovolaemic (p/c = thrist, tachycardia, reduced turgor, postural hypotension) – give sodium chloride IV
- o If hyponatraemic but not dehydrated (normovolaemic) = restrict fluid intake.
- o If hypervolaemic (p/c: raised JVP, oedema, HTN) – give diuretics, and fluid restrict.
- o Sudden correction of Na may = ‘central pontine myelinolysis’ (=encephalopathy, CN palsies, quadriplegia).
- o In chronic cases of hyponatraemia correct Na less than 0.5mmol/L per h.
- Serum sodium >145mmol/L
- o Hypovol: renal loss (=diuretics, post obstruction, osmotic diuresis), extra-renal loss (=sweating, burns, diarrhoea, fistula).
- o Normovol: renal loss (=diabetes insipidus, impaired thrist), extra-renal loss (=insensible loss from skin, respiratory tract)
- o Hypervol: sodium gains (=hypertonic NaCl, hypertonic dialysis, Cushing’s syndrome, hyperaldosteronsism).
- Again classify if patient is hypovol, normovol, or hypervol.
- Again, assessment of fluid status and dertermination of urinary sodium is essential in accurate diagnosis.
- o Identification of cause and cautious correction is indiacted.
- o Correct fluid deficit with physiological saline
- o If hypervolaemic hypernatraemic excess sodium requires removal with diuretics.
- o If euvolaemic hypernatraemic – give water IV as 5% dextrose.