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.
Mechanism: HES acts as a synthetic colloid to expand plasma volume through oncotic forces. * **Oncotic Pull:** Large HES molecules remain in the intravascular space โ **increase plasma oncotic pressure** โ draw fluid from the interstitial space into the blood vessels โ **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 โ fragments < 50,000 Daltons are rapidly excreted by the kidneys.
Dosing by species
- Shock bolus (resuscitation) ยท 5-10 mL/kg ยท IV ยท once ยท Administer slower than in dogs to avoid nausea/vomiting.
- Infusion ยท 1-2 mL/kg/hr; not to exceed 10 mL/kg in a 24 hour period ยท IV ยท CRI ยท 24 hours
- Emergent situations / Colloid oncotic pressure support ยท 10/mL/kg/day ยท IV ยท slow bolus over 15-30 minutes OR 24-hour infusion
- Shock resuscitation ยท 20 mL/kg ยท IV ยท bolus ยท Slower in the cat. Rapid administration to cats can cause nausea and vomiting.
- Adult horses - volume support ยท 8-10 mL/kg/day ยท IV ยท daily
- Foals - rapid volume support ยท 3-5 mL/kg ยท IV ยท once ยท In addition to crystalloids.
- Hypo-oncotic, well hydrated horses ยท 0.5-1 mL/kg per hour, up to 10 mL/kg/day ยท IV ยท CRI
- Volume replacement ยท 3-10 mL/kg ยท IV ยท once ยท Total daily doses of 10 mL/kg should not be exceeded due to risk for coagulopathies.
- Fluid resuscitation and management of hypoproteinemia ยท 8-10 mL/kg IV bolus or as a CRI at 0.5-1 mL/kg/hr (max. of 10 mL/kg/day) ยท IV ยท bolus or CRI
- Volume replacement ยท 10-15 mL/kg over 20-40 minutes, up to four times daily, OR 10-15 mL/kg bolus over 20-40 minutes followed by 1-2 mL/kg/hr continuous rate infusion ยท IV ยท up to q6h or CRI ยท Recommended maximum dose is 20 mL/kg/24 hours, though author notes exceeding this without side effects.
Routes of administration
Contraindications
- Severe heart failure
- Severe bleeding disorders
- Oliguric or anuric renal failure
Adverse effects
- Coagulopathies (prolonged PT/PTT, altered Factor VIII and von Willebrand Factor)
- Nausea and vomiting (especially in cats if administered too rapidly)
- Volume overload leading to pulmonary edema
- Hypersensitivity/anaphylactic reactions (rare)
- Falsely elevated serum amylase levels
- Transient increases in indirect serum bilirubin
- Potential risk for acute kidney injury (extrapolated from human data)
Drug interactions
- Whole Blood / Red Blood Cells ยท Do not administer Hextend simultaneously with blood through the same administration set due to a risk of coagulation.
Monitoring
- Fluid status (blood pressure, heart rate, capillary refill time, central venous pressure)
- Coagulation parameters (PT, PTT, platelet count), especially in high-risk patients or with high doses
- Clinical signs of pulmonary edema (respiratory rate/effort, lung auscultation)
- Blood gases
- Renal function (BUN, creatinine, urine output)
Overdose
Overdosage primarily results in **intravascular volume overload**, which can lead to pulmonary edema and congestive heart failure in susceptible patients. Treatment involves stopping the infusion, carefully monitoring fluid status, and administering diuretics (e.g., furosemide) if pulmonary edema develops.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.