WATER AND ELECTROLYTE DISTURBANCES
Hyponatraemia
Definition:
Hyponatraemia is a state where plasma sodium concentration is
less than 135 mmol/L.
Causes:
Hyponatraemia is the commonest electrolyte abnormality in
hospitalized patients. Usually this is dilutional hyponatraemia due to
defective renal water excretion as a result of excess secretion or
potentiation of ADH. The complete list of causes of hyponatraemia
classified according to changes in total body water include:
- Hypovolaemic Hyponatraemic states:
- Diuretic therapy.
- Mineralocorticoid deficit (Addison's disease).
- Salt-losing nephropathy (analgesic nephropathy, chronic
tubulo- interstitial nephritis, incomplete urinary tract
obstruction, after recovery from acute tubular necrosis and
after release of urinary obstruction). - Gastrointestinal losses (diarrhea or vomiting).
- Fluid loss in third space (peritonitis, ileus, burn or crush
injury).
In these conditions volume receptors are stimulated with
secretion of ADH which will then stimulate water
reabsorption from the distal nephron. This process will
continue even with development of hyponatraemia and