Chapter 9 Sodium and Water Balance, Fluid Compartments
(From Levy MN, Koeppen BM, Stanton BA: Berne & Levy Principles of Physiology, 4th ed. Philadelphia, Mosby, 2007, Fig. 38-1.)
Clinical note: In conditions associated with decreased arterial oncotic pressure (e.g., hypoalbuminemia in liver disease and nephrotic syndrome), fluid can shift from the intravascular space to the interstitium (so-called third spacing), resulting in edema, and often transcellular compartments such as the peritoneal cavity, resulting in ascites. If third spacing results in significant accumulation of fluid in compartments such as the peritoneal cavity or pleural space, the transcellular fluid volume becomes pathologically increased and the effective circulatory volume may become pathologically reduced, resulting in tissue hypoperfusion and prerenal azotemia.
Clinical note: In conditions associated with increased vascular permeability (e.g., infections, inflammatory states), proteins leave the intravascular space and enter the interstitium. If the lymphatics are unable to keep up with this transudation of fluid, interstitial edema results. In the lungs, this process can result in acute respiratory distress syndrome (ARDS).