Isotonic solutions are which of the following?

• A. Normal Saline
• B. Lactated Ringer's
• C. D5W
• D. Normal Saline, Lactated Ringer's, and D5W

Answer: (D)

Isotonic solutions have an osmolality similar to plasma, so they expand the extracellular fluid without causing water to move into or out of cells. Normal saline and lactated Ringer’s are classic isotonic crystalloids; they stay in the extracellular space and raise circulating volume without shifting fluid into cells.

D5W is a special case. In the bag it’s about isotonic, but once dextrose is metabolized, it leaves free water that distributes throughout body compartments, effectively becoming hypotonic. Despite that, many teaching settings list it among isotonic solutions because of its initial osmolarity in the bag. That’s why all three are grouped as isotonic in this context, with the caveat that D5W will become hypotonic after metabolism and isn’t used for sustained extracellular volume expansion.