Hartmann's solution or compound sodium lactate (CSL) is a crystalloid solution that is closely isotonic with blood and intended for intravenous administration. Hartmann's solution is used to replace body fluid and mineral salts that may be lost for a variety of medical reasons. It is especially suitable when the losses result in too much acid being present in the blood and is very similar—though not identical—to lactated Ringer's solution, the ionic concentrations of which differ slightly.