The nature of crystalloid and colloid solutions determines their ability to be absorbed by the cells or to remain in the circulatory system.
Crystalloids are aqueous solutions of mineral salts or other water-soluble molecules.
There are two classes of isotonic crystalloid solutions: 0.9%, sodium chloride (saline) and balance crystalloid solutions, in which chloride is replaced with a buffer, such as lactate, gluconate, or acetate to prevent hyperchloremic metabolic acidosis.
Among patients with sepsis, mortality at 90 days is not significantly difference between balanced crystalloid saline groups.
Colloids contain larger insoluble molecules, such as gelatin.
Oncotic pressure values are approximately 290 mOsm per kg of water, which slightly differs from the osmotic pressure of the blood that has values approximating 300 mOsm /L.
Crystalloid solutions contain small molecules that can pass freely through cell membranes and vascular system walls, so that they are useful as fluid expanders.
Crystalloid solutions are a source for electrolytes and a temporary source of fluid volume as they flow out of the vascular system quickly.
Lactated Ringer’s is an example of a crystalloid solution.
Colloid solution contain complex molecules and are much larger than those in crystalloid solutions.
Colloid solutions contain proteins, and are needed when a solution is required to remain in the vascular system.
Albumin is the most frequently used colloid in ICU settings.
Colloid solutions generally require refrigeration and can be stored for a limited period.
Whole human blood U.S.P. and Hetastarch are examples of colloid solutions.
In sepsis albumin, does not reduce mortality compared to saline.
In multiple randomized controlled trials, semi synthetic, colloid solutions, such as hydroxyethyl starch are associated with increased rates of acute kidney injury, replacement therapy, and death in patients with sepsis.