Which solution is hypertonic relative to plasma?

• A. 0.9% NSS
• B. Lactated Ringer's
• C. 5% NaCl
• D. D5W

Answer: (C)

Tonicity describes how a solution’s osmolality compares with plasma. A hypertonic solution has higher osmolality, so it pulls water out of cells into the extracellular space, increasing extracellular fluid.

Among the options, the one with 5% NaCl has a much higher osmolality than plasma, making it hypertonic. That’s why it draws water from cells and expands the extracellular fluid.

The others are not hypertonic to plasma: 0.9% NaCl and lactated Ringer’s are formulated to be isotonic with plasma, so they largely stay in the extracellular space without shifting water across cell membranes. D5W is initially considered isotonic in the bag, but after insulin/metabolism of the glucose, it becomes free water and behaves as hypotonic, not hypertonic.