Colloid fluids

Substances that do not dissolve into a true solution and do not pass through a semi-permeable membrane. Colloid solutions tend to remain in the intravascular compartment (within the circulation) longer than crystalloid solutions, and so a smaller amount may be needed to maintain an adequate intravascular volume. Colloids also increase colloidal osmotic pressure, and so draw water from the interstitial spaces into the intravascular compartment. However, when capillary permeability is increased, colloids may leak across the capillary membrane and increase interstitial oncotic pressure, causing oedema. This may also happen if too much colloid is given. Types of colloids include dextran and gelatin (e.g. Gelofusine® and Haemaccel®).