Which IV solution is not isotonic?

Which IV solution is not isotonic?

• A. 0.9% NaCl
• B. Lactated Ringer's
• C. 0.45% NaCl
• D. Dextrose 10% in water

Answer: (C)

Tonicity of IV fluids relative to plasma determines where the fluid will shift in the body. An isotonic solution has a similar osmolality to plasma, so it stays mainly in the intravascular space and expands circulation without moving water into or out of cells. A hypotonic solution has lower osmolality than plasma, so water moves from the blood into cells, which can cause the cells to swell. A hypertonic solution has higher osmolality, drawing water out of cells and into the intravascular space. The half-strength saline solution is hypotonic compared with plasma. Its lower osmolality means fluid tends to shift from the bloodstream into cells, causing cellular swelling. Because of this, it is not isotonic and is used in specific situations where free water replacement is needed, but it can lead to edema or hyponatremia if used inappropriately. In contrast, normal saline and lactated Ringer's are designed to be isotonic and generally remain in the vascular compartment to expand circulating volume. Dextrose 10% in water is hypertonic when given, initially drawing water out of cells into the extracellular space, and its effect changes after the dextrose is metabolized.

Tonicity of IV fluids relative to plasma determines where the fluid will shift in the body. An isotonic solution has a similar osmolality to plasma, so it stays mainly in the intravascular space and expands circulation without moving water into or out of cells. A hypotonic solution has lower osmolality than plasma, so water moves from the blood into cells, which can cause the cells to swell. A hypertonic solution has higher osmolality, drawing water out of cells and into the intravascular space.

The half-strength saline solution is hypotonic compared with plasma. Its lower osmolality means fluid tends to shift from the bloodstream into cells, causing cellular swelling. Because of this, it is not isotonic and is used in specific situations where free water replacement is needed, but it can lead to edema or hyponatremia if used inappropriately.

In contrast, normal saline and lactated Ringer's are designed to be isotonic and generally remain in the vascular compartment to expand circulating volume. Dextrose 10% in water is hypertonic when given, initially drawing water out of cells into the extracellular space, and its effect changes after the dextrose is metabolized.