Major losses of blood volume (hypovolemia) due to surgery, burns, or traumatic injuries, must be corrected immediately by giving infusions with blood volume substitutes (such as hydroxyethyl starch, HES).

Isotonic sodium containing crystalloid solutions when administered intravenously are distributed throughout the extracellular space and therefore have limited and transient plasma volume expanding capacity. By comparison, the colloids (eg. HES) are predominantly retained within the plasma volume, and are considered more effective as plasma volume expanders.