Third space loss?

Question

I keep hearing dif definitions, what is 3rd space loss, and what causes it?

Answer 1

The third space is the space between cells, essentially.  Third-spacing refers to the loss of fluid into the interstitial and out of intravascular spaces.  In other words, it means that fluids are going where they ought not to be--into spaces like the peritoneum, the lower legs, the pleura--anywhere but in the veins where they are supposed to be, doing their job of keeping up blood pressure and hydrating cells.

Water generally moves passively, so it will "leak" into any space that has a higher osmolality or a lower oncotic pressure.  So anything that alters either one of those factors can cause third spacing.