Volume Depletion versus Dehydration

You might think that these two terms are interchangeable, but you would, in fact, be wrong.

Dehydration

* Can be thought of as intracellular dehydration
* Is the loss of free water greater than the loss of sodium, which leads to hypertonicity
* Free water shifts from the intracellular space and leads to intracellular dehydration
* Most commonly is caused by poor fluid intake, fluid loss from sweating
* Patients are more likely to have altered mental status and thirst than in volume depletion
* Patients are less likely to have poor skin turgor than in volume depletion
* Best serum marker is sodium

Volume depletion

* Can be thought of as extracellular volume depletion
* Is the loss of free water proportionally to sodium
* Most commonly occurs with vomiting, diarrhea and hemorrhage
* Patients are more likely to have true orthostasis than with dehydration
* Patients are less likely to have altered mental status and thirst than with dehydration
* Patients are more likely to have poor skin turgor and oliguria than with dehydration
* Best serum marker is creatinine and GFR

Ref: Peterson and Hill 2011. Observation Medicine: The healthcare system's tincture of time. On line edition through ACEP- In press