Which is an isotonic IV solution?

• A. 0.45% NaCl
• B. D5NS
• C. 0.9% NaCl
• D. 3% NaCl

Answer: (C)

Isotonic IV solutions have osmolality similar to blood plasma, so they expand the extracellular fluid without shifting water into or out of cells. Normal saline (0.9% NaCl) matches plasma osmolality and stays mainly in the extracellular space, making it ideal for volume resuscitation and fluid replacement. A solution with half-normal saline (0.45% NaCl) is hypotonic, so it can cause water to move into cells and potentially lead to cellular swelling. Dextrose 5% in normal saline adds glucose, creating a higher osmolar load at administration, so it’s considered hypertonic (even though the effect can level out after glucose is metabolized). A 3% NaCl solution is hypertonic and draws water out of cells, used for specific conditions but not isotonic. Therefore, the isotonic choice is normal saline.