Which IV solution is hypertonic?

• A. 0.9% saline
• B. Lactated Ringer's
• C. 3% saline
• D. 5% dextrose in water

Answer: (C)

Understanding tonicity helps you predict how IV fluids affect cells. Hypertonic solutions have a higher osmolality than plasma, so water moves out of cells into the extracellular space, causing cells to shrink.

Normal saline and lactated Ringer’s are isotonic, meaning they have similar osmolarity to plasma and don't cause net water movement into or out of cells. A 3% saline solution is hypertonic because its salt concentration is much higher than plasma, leading to water shifting from cells into the bloodstream. Five percent dextrose in water isn’t hypertonic in the body; once the glucose is metabolized, it leaves free water, making the fluid effectively hypotonic.

So, the hypertonic IV solution is 3% saline.