Neuronal cells initially shrink in response to hypertonic extracellular fluid, but cell volume is restored within hours; an effect attributed to the generation of osmotically active substances within brain cells, called idiogenic osmoles.
Idiogenic Osmoles are intracellular organic molecules, e.g., Sorbitol, inositol, glycine. They are released from the cell in response to osmotic cell swelling, and synthesised in response to cell shrinking.
Once the cell volume is restored to normal, aggressive replacement of free water deficits can produce cell swelling and cerebral oedema.
To limit the risk of cerebral oedema, the decrease in plasma sodium should not exceed 0.5 mmol/L per hour.
