Hydroxyethyl Starch (HES)

**Hydroxyethyl Starch (HES)** is a synthetic colloid volume expander derived from a waxy starch composed primarily of amylopectin. It is used in veterinary critical care to treat hypovolemia and provide oncotic support. **Key Clinical Features:** * **Intravascular Persistence:** HES provides better and more prolonged intravascular volume expansion compared to crystalloid fluids. * **Capillary Leak Syndromes:** It can help reduce vascular permeability and downregulate pro-inflammatory mediators in patients with systemic inflammation. * **Molecular Weight & Substitution:** Products are classified by their mean molecular weight (MW) and degree of substitution (DS) (e.g., HES 450/0.7, HES 130/0.4). Higher MW and DS generally prolong intravascular half-life but increase the risk of coagulopathies. > **Clinical Pearl:** In recent years, the use of synthetic colloids like HES has declined in both human and veterinary medicine due to human studies linking HES to an increased risk of **acute kidney injury (AKI)** and mortality, particularly in septic patients. While veterinary data is less conclusive, many critical care specialists now use HES more conservatively.

กลไกการออกฤทธิ์: HES acts as a synthetic colloid to expand plasma volume through oncotic forces. * **Oncotic Pull:** Large HES molecules remain in the intravascular space → **increase plasma oncotic pressure** → draw fluid from the interstitial space into the blood vessels → **expand circulating blood volume**. * **Enzymatic Degradation:** To prevent rapid breakdown, the glucose units of amylopectin are substituted with hydroxyethyl ether groups. * **Metabolism:** Larger molecules are slowly degraded by **serum alpha-amylase** into smaller fragments → fragments < 50,000 Daltons are rapidly excreted by the kidneys.

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