The term colloid fluid refers to a sterile water solution with macromolecules added that pass the capillary wall only with great difficulty. The osmotic strength of the macromolecules is not great and, therefore, a colloid fluid must also contain electrolytes to be non-hemolytic. As long as macromolecules reside inside the capillary wall their contribution to the total osmolality (the colloid osmotic pressure) is still sufficient to distribute a large proportion of the infused fluid volume inside the bloodstream.
Colloid fluids are used as plasma volume expanders and have more long-lasting effect than crystalloid fluids. They carry a risk of allergic reactions not shared by crystalloid fluids.
Albumin is the most abundant protein in plasma and, therefore, has an important role in maintaining the intravascular colloid osmotic pressure.
Long chains of glucose molecules (polysaccharides) are synthesized by bacteria to serve as macromolecules in the group of infusion fluids called the dextrans.
Hydroxyethyl starch (HES) also consists of polysaccharides and is prepared from plants, such as grain or maize. The variability in chemical composition determines the differences in clinical effect between the solutions. Hetastarch contains the largest molecules (450 kD) and pentastarch intermediate-sized molecules (260 kD). The most recently developed HES preparations have an even lower molecular size, 130 kD on the average.
Cambridge: Cambridge University Press , 2011. 11-17 p.