Why is isotonic saline used in volume resuscitation instead of hypotonic solutions?

• A. To rapidly correct hypernatremia.
• B. To cause cellular edema to trap fluids.
• C. To decrease blood pressure by diluting blood.
• D. To expand intravascular volume safely and restore perfusion without causing cellular edema.

Answer: (D)

When resuscitating a patient who is volume-depleted, the goal is to rapidly increase circulating blood volume to improve tissue perfusion without causing water to move into cells and cause edema. Isotonic saline has roughly the same osmolality as plasma, so it stays primarily in the extracellular space, increasing intravascular volume and improving preload and perfusion without shifting fluid into cells. Hypotonic solutions, with lower osmolality, draw water into cells, risking cellular swelling (including brain edema) and not reliably expanding the vascular compartment. Therefore isotonic saline expands intravascular volume safely and restores perfusion without causing cellular edema.