Fig. 2
From: Acute Dysnatremias - a dangerous and overlooked clinical problem
Dysnatremia and the effects on the brain. In normal condition, there is osmotic equilibrium. Water diffuses between the extracellular volume (ECV) and intracellular volume (ICV). In acute hyponatremia, water from ECV diffuses into ICV (water is drawn into cells), which can lead to brain edema and herniation. In acute hypernatremia, water from ICV diffuses into ECV (water is extracted from the cells), which can lead to reduced brain volume. This can cause rupture of cerebral veins, focal and subarachnoid bleeding. Upon rapid correction of acute hyponatremia or acute hypernatremia, the brain can be returned to normal condition (normonatremia)