Hydroxyethyl starch

Hydroxyethyl starch (HES) is a polymer of glucose subunits, administered in balanced electrolyte solutions, which has a number of medical applications. Among the most common is as a plasma expander, not as a total substitute for plasma and its immune and coagulation factors, but as a means of treating hypovolemia or relative hypovolemia, to provide acute normovolemic hemodilution, or to serve priming fluids for external devices that process blood. One common commercial preparation is Hextend, made of 6% HES in a balanced electrolyte mixture.

It has no oxygen-carrying capacity. From a colloidal standpoint, dextran 70 has comparable properties, but hetastarch is stable over a wider temperature range, and has little antigenic effect. "Hetastarch appears to be comparable with albumin as a plasma volume expander." 5% albumin injection, however, is considerably more expensive, and its supply is more unpredictable.

Side effects

HES is not free of side effects, although some side effects come from the carrier fluid. Independently of the carrier fludi, Vomiting, mild temperature elevations, chills, itching, submaxillary and parotid gland enlargement, mild influenza-like symptoms, headache, myalgia, peripheral edema of the lower extremities, and anaphylactoid reactions manifested as periorbital edema, urticaria, and wheezing have been reported.

Laboratory

Hetastarch increases the erythrocyte sedimentation rate more than dextran 75, and it may increase prothrombin, partial thromboplastin, bleeding and clotting times. Large volumes decrease hematocrit, plasma proteins, platelet counts, and hemoglobin.

Clinical

Since it depletes or dilutes coagulation factors, some neurosurgeons recommend against its use in patients for whom intracranial hemorrhage may be critical, and those that permit its use suggest limiting it to a few days. If coagulation factors are provided through other fluids, the risk may be reduced.

Carrier fluid

An open-label Phase I study compared Hextend to 6% HES in normal saline. Two-thirds of the volunteers that received HES in saline developed hyperchloremic metabolic acidosis, but none of those who received Hextend.

Military field medicine

Hextend is the standard intravenous fluid in the combat lifesaver kit of the U.S. Army, for soldiers that provide a bridge between first aid and the initial level of fully qualified medical technicians.