Crystalloids vs colloids: which statement is true?

Crystalloids vs colloids: which statement is true?

• A. Colloids distribute equally between intravascular and interstitial spaces
• B. Crystalloids remain predominantly in the intravascular space
• C. Colloids stay intravascular longer than crystalloids
• D. Both distribute identically

Answer: (C)

Understanding how IV fluids distribute between the intravascular and interstitial spaces is the key idea. Crystalloids are small molecules that freely cross capillary walls, so after infusion they quickly equilibrate with the interstitial space. Only a fraction remains in the intravascular compartment over time, meaning you need larger volumes to sustain plasma volume expansion and you don’t get long-lasting intravascular volume from a small amount. Colloids, on the other hand, contain large molecules that create oncotic pressure, pulling water into the vascular space and restricting its movement into the interstitium. This keeps them in the intravascular compartment longer, producing a more durable increase in plasma volume with less total fluid infused. That’s why the true statement is that colloids stay intravascular longer than crystalloids. The other options falsely describe equal or predominant intravascular distribution for crystalloids or suggest identical distribution for both.

Understanding how IV fluids distribute between the intravascular and interstitial spaces is the key idea. Crystalloids are small molecules that freely cross capillary walls, so after infusion they quickly equilibrate with the interstitial space. Only a fraction remains in the intravascular compartment over time, meaning you need larger volumes to sustain plasma volume expansion and you don’t get long-lasting intravascular volume from a small amount.

Colloids, on the other hand, contain large molecules that create oncotic pressure, pulling water into the vascular space and restricting its movement into the interstitium. This keeps them in the intravascular compartment longer, producing a more durable increase in plasma volume with less total fluid infused.

That’s why the true statement is that colloids stay intravascular longer than crystalloids. The other options falsely describe equal or predominant intravascular distribution for crystalloids or suggest identical distribution for both.