Which IV fluid is hypertonic relative to plasma?

• A. 5% NaCl
• B. 5% LR
• C. 10% H2O
• D. -0.45% NaCl

Answer: (A)

Tonicity is about how the osmolality of an IV fluid compares with plasma. Hypertonic solutions have higher osmolality than plasma, so they pull water out of cells into the extracellular space, increasing circulating volume and serum sodium.

5% NaCl is a hypertonic saline solution with a very high osmolality (about 1.7 Osm/L), far above normal plasma (~0.275–0.295 Osm/L). That’s why it’s considered hypertonic relative to plasma.

Lactated Ringer’s is designed to be isotonic, with an osmolality close to plasma, so it doesn’t cause a water shift out of cells. A solution of 0.45% NaCl is hypotonic, leading water to move into cells rather than out. A 10% dextrose in water is initially hypertonic in the bag, but glucose is rapidly metabolized, so the osmotic effect isn’t sustained; the standout hypertonic option remains the 5% NaCl.