Hyperosmolar states.

The composition of the extracellular fluid (ECF) must remain stable for cells to function properly. In normal individuals vasopressin and thirst zealously maintain the total ECF concentration, or osmolality, within a narrow range. Disruption of these regulatory mechanisms or rapid addition of solute to the ECF can lead to hyperosmolality. The serious neurologic symptoms that accompany many forms of hyperosmolality can be explained by understanding the physiologic response of cells to the osmotic stress. This review describes the physiology, pathophysiology, differential diagnosis, and therapy of hyperosmolar states.