Hypernatraemia
Hypernatraemia is considered when plasma sodium is more than
145 mmol/litre.
Causes:
Hypernatraemia is usually a consequence of water depletion and-to
much lesser extent- is due to excess sodium intake. In normal situations
water loss (renal or non-renal) or excess sodium intake will induce
hyperosmolar state with stimulation of osmoreceptors which will lead to
thirst (water intake) and secretion of ADH (water reabsorption from the
distal nephron). Water gain will correct the hyperosmolar state and
hypernatraemia will not persist. Hypernatraemia persists only when either
water intake is not possible (unconscious, very young or very old patient
unable to ask for water or absent water supply) or when there is a lesion
affecting thirst center in the hypothalamus (tumour) or abnormal
osmoreceptors (essential hypernatraemia).
A- Renal causes of water loss:
- Osmotic diuresis
- Enteral (through a nasogastric tube) or parenteral
(intravenous hyperalimentation) feeding, usually hypertonic
constituents are used. - Hyperglycaemia
- Enteral (through a nasogastric tube) or parenteral
- Nephrogenic diabetes insipidus (NDI) which results in renal
tubular concentration defect. This could be due to:
a. Toxin e.g. drug (lithium, amphotericin, demeclocycline) or
Bence-Jones protein.