How Do Crystalloids and Colloids Work?

Crystalloids fluids such as normal saline typically have a balanced electrolyte composition and expand total extracellular volume. Colloid solutions (broadly partitioned into synthetic fluids such as hetastarch and natural such as albumin) exert a high oncotic pressure and thus expand volume via oncotic drag.

How do Crystalloids work?

Crystalloid fluids function to expand intravascular volume without disturbing ion concentration or causing significant fluid shifts between intracellular, intravascular, and interstitial spaces. Hypertonic solutions such as 3% saline solutions contain higher concentrations of solutes than those found in human serum.

How do colloid fluids work?

Colloids are gelatinous solutions that maintain a high osmotic pressure in the blood. Particles in the colloids are too large to pass semi-permeable membranes such as capillary membranes, so colloids stay in the intravascular spaces longer than crystalloids.