Wednesday, April 22, 2009

Hypovolemia versus Dehydration

It is important to realize the difference between HYPOVOLEMIA and DEHYDRATION, two terms which are often used interchangeably but in fact reflect different things. Read the Up-To-Date entry « Dehydration is not synonymous with hypovolemia » by Burton Rose if there is any confusion about this. HYPOVOLEMIA refers to any condition in which the extracellular fluid volume is reduced, and results in decreased tissue perfusion. It can be produced by either salt and water loss (e.g. with vomiting, diarrhea, diuretics, or 3rd spacing) OR by water loss alone, which is termed DEHYDRATION. Salt + water loss comes primarily from the extracellular fluid whereas pure water loss (dehydration) come from the total body water, only about 1/3 of which is extracellular. Thus for dehydration to produce the same degree of extracellular volume depletion as salt+water loss, 2.5 times as much fluid needs to be lost. Patients with DEHYDRATION are always hypernatremic.


MSIII said...

Very nicely explained. Thank you!

Joe SRNA said...

Good explanation. Nice to have easy access to it, away from the hospital.

Anonymous said...

So when somebody gets sick (vomiting, diarrhea) and says they are "dehydrated," they should say they are "volume depleted," correct?
If dehydration is the loss of water, what causes dehydration? Everything I can think of causes volume depletion, not dehydration. or is dehydration the loss of water AND solutes (mainly sodium), just that the water is greater PROPORTIONATELY than the sodium loss?
is dehydration a kind of volume depletion? but volume depletion isn't necessarily dehydration?

Anonymous said...

I have recently suffered wat is thought to be a hypovolemic shock attack,i imbibe large amounts of caffeine,smoke,am under stress,large wk-load am constantly tired and was dehydrated at time of attack when I collapsed without any seizure acivity.i was curious if I met any of the perameters for hypovolemic shock as all other tests came back good?????