Hydroxyethyl starch also called HES or Hetastarch is a complex mixture of ethoxylated amylopectin of various molecular sizes; average MW 4.5 lac (range 10,000 to 1 million).
The colloidal properties of 6% HES approximate those of human albumin. Plasma volume expands slightly in excess of the volume infused. This happens as extra vascular fluid is sucked into the blood vessels when this is infused because its oncotic pressure.
Hence it is used in hypotensive emergencies when the low blood pressure is caused by a decrease in intra cascular volume.
Basically it is a colloid that increases the intravascular volume when transfused for longer duration than the other type of intra venous fluids called as crystalloids.
Haemodynamic status is improved for 24 hour or more with Hydroxyethyl starch or Hetastarch.
Smaller molecules (MW < 50,000) of Hydroxyethyl starch are excreted rapidly by kidney; 40% of infused dose appears in urine in 24 hr.
Larger molecules are slowly broken down to smaller ones and eliminated with a t½ of 17 days.
Hydroxyethyl starch adverse effects are vomiting, mild fever, itching, chills, flu like symptoms, swelling of salivary glands. Urticaria, periorbital edema and bronchospasm are the anaphylactoid reactions.
Hydroxyethyl starch has also been used to improve harvesting of granulocytes because it accelerates erythrocyte sedimentation. EXPAN 6% inj (100, 500 ml vac)