Fluids, nutrients, and waste products constantly shift within the body's compartments—from the cells to the interstitial spaces, to the blood vessels, and back again. A change in one compartment can affect all the others.
Keeping track of the shifts
That constant shifting of fluids can have important implications for patient care. For instance, if a hypotonic fluid, such as half-normal saline solution, is given to a patient, it may cause too much fluid to move from the veins into the cells, and the cells can swell. On the other hand, if a hypertonic solution, such as dextrose 5% in normal saline solution, is given to a patient, it may cause too much fluid to be pulled from cells into the bloodstream, and the cells shrink.
For more information about IV solutions, see chapter 19, IV fluid replacement.