2020 Dec 15. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan–.
Hypovolemia refers to a state of low extracellular fluid volume, generally secondary to combined sodium and water loss. All living organisms must maintain an adequate fluid balance to preserve homeostasis. Water constitutes the most abundant fluid in the body, at around 50% to 60% of the body weight. Total body water is further divided into the intracellular fluid (ICF), which comprises 55% to 75%, and the extracellular fluid (ECF), which comprises around 25-45%. The ECF is further divided into the intravascular and extravascular (interstitial) spaces. ECF is the more readily measured component as it can be estimated by arterial blood pressure.