Which type of crystalloid would most likely cause intracellular swelling?

• A. Isotonic
• B. Hypertonic
• C. Hypotonic
• D. None

Answer: (C)

The key idea is how osmosis works across cell membranes. Water moves from areas of lower solute concentration (more water) to areas of higher solute concentration (less water) to balance osmolality. A hypotonic crystalloid has a lower osmolality than plasma, so when it’s in the extracellular space, water shifts into cells to equalize the gradient. That influx of water causes intracellular swelling. In contrast, isotonic solutions don’t change cell size much because their osmolality is similar to plasma, and hypertonic solutions draw water out of cells, causing shrinkage. So a hypotonic fluid is the one that would most likely cause intracellular swelling.