Hypovolemia hypernatremia

In general, hypernatremia arises in the setting of (1) hypovolemia (either excessive water loss or failure to replace normal water losses), (2) hypervolemia (a net Na gain in excess of water gain), or (3) normovolemia. Again, assessment of TB W status by physical examination and measure-... 

Hypernatremia in the setting of decreased ECF is caused by the renal or extrarenal loss of hypoosmotic fluid leading to dehydration. Thus once hypovolemia is established, measurement of urine Na" " and osmolality is used to determine the source of fluid loss. Patients who have large extrarenal losses have a concentrated urine (>800 mOsmol/L) with low urine Na (<20 mmol/L), reflecting the proper renal response to conserve Na and water as a means to restore ECF volume. Extrarenal causes include diarrhea, skin (burns or excessive sweating), or respiratory losses coupled with failure to replace the lost water. When gastrointestinal loss is excluded, and the patient has normal mental status and access to H2O, a hypothalamic disorder (tumor or granuloma) should be suspected, because the normal thirst response should always replace insensible water losses. 

The goals in treating patients with hypernatremia include correction of the serum sodium concentration at a rate that restores and maintains cell volume as close to normal as possible, as well as normalizing the ECF volume in states of ECF volume depletion and expansion. Adequate treatment should result in the resolution of symptoms associated with hypovolemia. Careful titration of fluids and medications should minimize the adverse effects from too rapid correction. Modulation of dietary sodium intake and sodium replacement may be necessary to prevent recurrence of hypernatremia. 

A loss of fluid from the body without loss of sodium can lead to hypovolemia and concentration of sodium and hypernatremia. Fluid then is hypertonic and can cause cellular shrinkage owing to fluids moving out of cells in an attempt to balance the hypertonic fluid. The symptoms of fluid imbalance can be accompanied by symptoms of electrolyte imbalance and shifts in other electrolytes that occur in an attempt to balance electrolytes. 

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