Which fluid is NOT listed as an isotonic crystalloid in the material?

• A. Lactated Ringer's Solution
• B. Normosol
• C. 0.9% NaCl
• D. D5W (Dextrose in Water)

Answer: (D)

Isotonic crystalloids have an osmolality close to that of blood plasma, so they expand the extracellular fluid without causing water movement into or out of cells. Lactated Ringer's and Normosol are balanced crystalloids that provide electrolytes and buffer precursors, keeping their osmolarity near plasma. Normal saline (0.9% NaCl) is also isotonic and commonly used for fluid resuscitation.

D5W, or 5% dextrose in water, behaves differently. Its dextrose is rapidly metabolized after administration, leaving mostly free water. This leaves the solution with a lower effective osmolality, making it hypotonic to plasma over time. Because of that shift, it is not classified as an isotonic crystalloid for fluid resuscitation, which is why it is the correct choice.