What characterizes isotonic fluids?

Isotonic fluids are characterized by having a tonicity that is equal to that of plasma in the body. This means that the concentration of solutes in the isotonic fluid is similar to the concentration of solutes found in the blood plasma. When isotonic fluids are administered, they neither cause cells to shrink (which would happen with hypertonic fluids) nor swell (which would occur with hypotonic fluids). This balance is essential for maintaining homeostasis, particularly in critical care situations where proper fluid balance is crucial for patient outcomes.

In contrast, options that describe higher or lower concentrations of solutes compared to plasma do not describe isotonic fluids accurately, as isotonic fluids must maintain equal concentration. Additionally, while isotonic solutions can contain electrolytes, the absence of electrolytes is not characteristic of isotonic fluids; rather, many isotonic solutions include essential electrolytes, contributing to their usefulness in clinical settings.