The term crystalloid fluid refers to sterile water solutions that contain small molecules, such as salt and glucose, which are able to crystallize. These solutes easily pass though the capillary membrane, which is the thin fenestrated endothelium that divides the plasma volume (PV) from the interstitial fluid volume. This process of solute distribution brings along water. Hence, the volume of a crystalloid fluid is spread throughout the extracellular fluid (ECF) space.
Ringer´s solution is a composition created by Sydney Ringer in the 1880s to be as similar as possible to the ECF. Hartmann later added a buffer, lactate, to the fluid and made it “Hartmann´s solution” or “lactated “Ringer´s solution”. Ringer solutions distribute from the plasma to the interstitial fluid space in a process that requires 25-30 min to be completed. The half-life in plasma is approximately 8 min. In contrast, elimination is greatly retarded during surgery where Ringer´s always exhibit two-compartment kinetics.
Glucose (dextrose) solutions are used to administer calories to prevent starvation, and also to provide body water. They are the only available infusion fluids that add volume to both the ECF and the ICF volumes. Infused glucose distributes rapidly over 2/3 of the expected ECF space. Elimination occurs by insulin-dependent uptake to the body cells. The half-life is 15 min in healthy volunteersbut twice as long during surgery. The basic need for glucose in an adult corresponds to 4 L of 5% glucose per 24 hours (800 kcal) which prevents blunt starvation while not providing adequate nutrition.
The hypertonic nature of 15% mannitol has made it a means of acutely reducing the intracranial pressure in patients with head trauma.
Cambridge: Cambridge University Press , 2011. 1-10 p.