1. Hypovolemia: oligemia; Oligemia: Olighemia, Oligohemia: a deficiency in the amount of blood in the body Hypovolemia, defined as an absolute reduction in extracellular fluid (EFC) volume, is the most common cause of prerenal failure. Hypovolemia is usually caused by the loss of whole blood (hemorrhage) or by abnormal loss of extracellular fluid from the gastrintestinal tract, skin or kidney