Dextrans

Dextran 70 (Macrodex), with a molecular mass of about 70,000 daltons, is an effective volume expander. However, after infusion of more than 20 mL/kg in 24 hours, dextran 70 may interfere with normal blood clotting, causing a deficiency with crossmatching procedures and possibly causing a bleeding diathesis. These clotting defects reflect reduced platelet adhesiveness resulting from an antithrombin effect. The incidence of severe anaphylactoid or anaphylactic reactions is a concern.^[153] These reactions are mediated by dextran-reactive antibodies that are IgG immunoglobulins. Dextran-reactive antibodies are formed in response to dextran polysaccharides. This process can be prevented if the potentially reactive sites on the dextran-reactive antibody are blocked before the antibody is given. By prior administration of a hapten, a substance capable of combining with immunoglobulins but not producing a reaction, the reactive sites are occupied and unable to react to the antigen. Prior administration of dextran I (Promit, molecular mass of 1000 daltons) has proved effective as a hapten and decreases, but does not eliminate, the incidence of severe reactions. ^{[154] [155]} Dextran 70 exerts a higher colloid osmotic pressure than blood. Dextran 70 and albumin may deplete the extracellular fluid space of water, as does albumin.

Dextran 40 (Rheomacrodex), with a molecular mass of 40,000 daltons, has been used primarily to reduce blood viscosity and cellular aggregation and to improve microcirculation during low-flow states. It is often given prophylactically to decrease the incidence of postoperative thromboembolism. Blood viscosity may be increased by trauma, blood loss, burns, and endotoxin shock. Although viscosity can be decreased by dextran 40, the presumed improvement in flow through the microcirculation has not been well documented.