What is the primary purpose of administering colloids such as hetastarch?

• A. Decrease blood viscosity
• B. Increase colloid osmotic pressure and draw fluid into the vascular space
• C. Dilute plasma electrolytes
• D. Replace crystalloids

Answer: (B)

Colloids like hetastarch are used to rapidly expand the circulating blood volume by increasing the colloid osmotic (oncotic) pressure inside the vessels. Their large molecules stay mainly in the intravascular space, pulling fluid from the interstitial and intracellular compartments into the vascular space. This makes them especially effective for treating hypovolemia or shock with a smaller total volume compared to crystalloids. The primary goal is to draw and retain fluid within the vessels, not to dilute electrolytes, and not to replace crystalloids.