Colloid replacement in the ICU

Colloids are fluids containing large molecular weight molecules that do not readily cross the capillary membrane. Colloid replacement is becoming increasingly more common in the equine intensive care unit. Advantages of colloid therapy include improved oncotic pressure, rapid intravascular volume replacement, and improved microvascular perfusion. Edema formation is minimized through the use of colloids, rather than crystalloids, in the volume resuscitation of hypoproteinemic animals. Available colloids include both natural (biologic) and synthetic formulations. Plasma is the most common biologic colloid utilized in horses, and offers the advantage of providing a broad range of proteins in addition to its principle colloid, albumin. These additional proteins include coagulation factors, antithrombin, and immunoglobulins. The most widely used synthetic colloid in horses is hydroxyethyl starch (hetastarch). Side effects of hetastarch include dose-dependent effects on coagulation, primarily because of decreases in factor VIII and von Willebrand factor concentrations. Other synthetic or semisynthetic colloids include pentastarch, dextrans, and a polymerized ultrapurified bovine hemoglobin product. Monitoring of patients receiving colloid therapy should include direct colloid osmometry. Indirect estimates of colloid osmotic pressure are not reliable in critically ill patients and in those receiving synthetic colloids. Total protein measurements do not account for the oncotic contribution of synthetic colloids.