Hydroxyethyl Starch

Hydroxyethyl starch (hetastarch) is a synthetic colloid solution in which the molecular mass of at least 80% of the polymers ranges from 10,000 to 2,000,000 daltons. It is available in the United States as a 6% solution in 0.9% sodium chloride (Hespan). The pH of hetastarch is about 5.5, and the osmolarity is about 310 mOsm/L. The larger molecules are degraded enzymatically by amylase. It is stored in the reticuloendothelial system for several hours and is believed to be renally excreted. It produces dilutional effects similar to other volume expanders and reduces factor VIII:C levels by 50% in a dose of 1 L, with prolongation of the partial thromboplastin time.^[124] Hetastarch can also interfere with clot formation by direct movement into the fibrin clot of the hetastarch molecules. In clinically recommended volumes (i.e., 20 mL/kg), there is minimal interference with subsequent crossmatching. Repeated doses can result in accumulation and side effects, which include allergic reactions and bleeding as described with higher doses (20 to 25 mL/kg).

A new form of hydroxyethyl cellulose has been approved for use in the United States. Hextend (Biotime, Berkeley, CA) contains 6% hetastarch in a solution that approaches physiologic concentrations of the major electrolytes. It also contains physiologic levels of glucose and lactate as a buffer. In contrast to Hespan, Hextend polymer units have an average molecular mass of 670 kd, with 80% within the range of 20 to 2500 kd, making these units significantly smaller than Hespan. Early studies have suggested that Hextend might not affect the coagulation process to the same degree as Hespan. In a study of 90 patients undergoing major surgery, those who were given Hextend had no significant change in their thromboelastogram profiles. Patients receiving lactated Ringer's solution were found to be hypercoagulable, and those receiving Hespan were found to be hypocoagulable compared with baseline. ^[120] This difference may be caused by the significantly smaller molecular mass of Hextend particles compared with Hespan, but more data are needed to form sound conclusions.