Isotonic IV fluids have which characteristic compared with plasma?

• A. They have higher osmolality than plasma.
• B. They have lower osmolality than plasma.
• C. They have the same osmolality as plasma.
• D. They contain no solutes

Answer: (C)

Isotonic IV fluids are defined by having the same osmolality as plasma, so they do not cause water to shift into or out of cells. This means they stay mainly in the extracellular space and primarily expand intravascular volume, which is why they’re used to treat hypovolemia. If a solution had higher osmolality than plasma, it would be hypertonic and draw water out of cells, potentially shrinking cells and drawing fluid into the vascular space. If a solution had lower osmolality, it would be hypotonic and cause water to move into cells, risking swelling. A solution with no solutes would be essentially pure water, which would rapidly dilute plasma and disrupt red blood cells, making it unsuitable for IV use.