Crystalloids are basically electrolytes in water. Colloids are crystalloids with high molecular weight (MW) polymers added.
Because of the high MW, colloids remain in the circulation for several to many hours.
Use crystalloids for resuscitation, replacement, and maintenance fluid therapy. Crystalloids quickly move out of the vascular space. Examples include 0.9% saline, lactated Ringer’s, Plasmalyte, etc. The exact composition of the fluid varies with type.
Use colloids for resuscitation in addition to crystalloids and when protein levels are low to improve colloid osmotic pressure and prevent fluid loss out of the circulation and extravascular fluid accumulation.
Crystalloids can be hypo-, iso-, or hypertonic in comparison to blood/plasma.
Dextrose solutions are NOT crystalloids, they are basically just water after the dextrose is metabolized.
