Which IV fluid is hypotonic relative to plasma?

• A. 0.23% NaCl
• B. 0.33% NaCl
• C. 0.9% NSS
• D. 5% H2O

Answer: (A)

Tonicity is about how osmolarity of a solution compares to the blood. A hypotonic fluid has a lower osmolality than plasma, so water moves into cells and they tend to swell.

The 0.23% NaCl solution has far fewer solutes per liter than plasma, giving it a much lower osmolarity. That makes it hypotonic relative to plasma, so when it’s given, water shifts from the bloodstream into cells, potentially causing cells to swell. This is why 0.23% NaCl is considered hypotonic. By comparison, normal saline is isotonic, and a solution like 5% dextrose in water behaves as free water in the body (and becomes hypotonic after the glucose is metabolized). The take‑home is that the lowest-osmolarity option among the choices is the hypotonic one, which in this case is the 0.23% NaCl solution.