An elderly person confined to an unairconditioned room in the summer may suffer
From dehydration that develops over hours or days : ECF volume decreases and its
osmolarity increases.
Brain shrinkage will occur and may be so severe that there is intracerebral hemorrhage from torn blood vessels
Regulatory volume increase of brain cells involves synthesis and accumulation of additional intracellular organic osmolyte
If the patient is brought into the ER , the decreased volume and increased osmotic concentration of his ECF may be rapidly corrected.
Rapid water entry into brain cells will then cause drastic swelling and possible death.
Moral : osmotic of extracellular fluid must be corrected slowly