hypoosmolality owing to the fact that volume receptors are
more potent than the osmoreceptors.
- Hypervolaemic (oedematous) Hyponatraemic states:
- Liver cirrhosis
- Congestive heart failure.
• Nephrotic syndrome ....................................................
- Renal failure with water overload.
In these conditions, although total body water is increased, the
effective circulating blood volume is decreased as the excess fluid
is extravascular and is interstitial. The decreased effective
circulating volume results in excessive stimulation and secretion of
ADH with more water retention.
- Euvolaemic (Normal volume) Hyponatraemic States:
- Hormonal (Myxoedema, glucocorticoid deficiency or exogenous
ADH vasopressin).
- Massive water load (psychogenic polydipsia, parenteral fluid or
excessive water absorption during bladder irrigation at
transurethral prostatectomy).
- Syndrome of inappropriate secretion of ADH (SIADH)
- Essential hyponatraemia: Occurs mostly with chronic illness,
under nutrition or with T.B. There is a resetting of the osmostat
(in the hypothalamus) for lower level of osmolality and
consequently lower plasma sodium concentration.
