Hypernatremia occurs when the serum sodium level exceeds 148 mEq/L. The osmolality in hypernatremia generally exceeds 295 mOsm/kg because it is an imbalance between the sodium and water levels in the body. Hypernatremia may be caused by either a greater loss of water compared with salt or an acute gain of salt compared with water. Table 12-1lists examples of theses causes. If sodium levels are increased, water flows via osmosis from inside and around the cell into the intravascular compartment. This results in intracellular and interstitial dehydration and may potentially lead to hypervolemia as fluid flows into the intravascular space.