<P> Patients who undergo long, difficult operations in large surgical fields can collect third - space fluids and become intravascularly depleted despite large volumes of intravenous fluid and blood replacement . </P> <P> The precise volume of fluid in a patient's third spaces changes over time and is difficult to accurately quantify . </P> <P> Third spacing conditions may include peritonitis, pyometritis, and pleural effusions . Hydrocephalus and glaucoma are theoretically forms of third spacing, but the volumes are too small to induce significant shifts in blood volumes, or overall body volumes, and thus are generally not referred to as third spacing . </P>

The total body water is divided into intracellular and extracellular fluids