Which of the following types of intravenous solutions is isotonic?

Isotonic intravenous solutions are those that have an osmolarity similar to that of the body's blood plasma, typically around 270-300 mOsm/L. These solutions help maintain fluid balance without causing cells to swell or shrink due to osmosis.

Normal Saline, which consists of 0.9% sodium chloride, is widely recognized as an isotonic solution. Its osmolarity closely matches that of human blood plasma, making it suitable for a variety of medical applications, including fluid resuscitation, maintaining hydration, and as a vehicle for medication administration. When administered, it helps expand extracellular volume without significantly disrupting fluid balance within cells.

In contrast, 5% Dextrose in Water is initially isotonic, but it quickly becomes hypotonic once metabolized, as the dextrose is utilized by the body's cells, leaving free water. Similarly, 0.45% NaCl is hypotonic and can result in cell swelling if administered as the primary fluid replacement solution. Lastly, 10% Dextrose in Water is hypertonic and can lead to cellular dehydration due to its high concentration of solutes compared to blood plasma.