Hypovolemia
In physiology and medicine, hypovolemia (also hypovolaemia, oligemia or shock) is a state of decreased blood volume; more specifically, decrease in volume of blood plasma. It is thus the intravascular component of volume contraction (or loss of blood volume due to things such as hemorrhaging or dehydration), but, as it also is the most essential one, hypovolemia and volume contraction are sometimes used synonymously.
Hypovolemia is characterized by salt (sodium) depletion and thus differs from dehydration, which is defined as excessive loss of body water.
Causes
Common causes of hypovolemia are
Loss of blood (external or internal bleeding or blood donation)
Loss of plasma (severe burns and lesions discharging fluid)
Loss of body sodium and consequent intravascular water; e.g. diarrhea or vomiting
Vasodilation (involving widening of blood vessels) such as trauma leading to disfunction of nerve activity on blood vessels and inhibition of the vasomotor center in the brain or drugs such as vasodilators typically used to treat hypertensive individuals.
