Florida State Paramedic Practice Exam

Which of the following is considered an isotonic solution?

1. 0.45% Normal Saline

2. D5W

3. 0.9% Normal Saline

4. Plasma

The correct answer is: 0.9% Normal Saline

An isotonic solution is one that has a similar osmotic pressure to that of the body's own fluids, which helps maintain fluid balance without causing cells to swell or shrink. In this context, 0.9% Normal Saline is commonly recognized as an isotonic solution because its concentration of sodium chloride is similar to that of plasma and extracellular fluid. This characteristic makes it a preferred choice for fluid resuscitation and volume replacement in various medical situations. 0.45% Normal Saline is a hypotonic solution, meaning it has a lower concentration of solutes compared to normal body fluids, which can lead to fluid moving into cells and potentially causing them to swell. D5W contains dextrose in water and is initially isotonic, but once metabolized, it becomes hypotonic. Plasma, while it is isotonic in its natural state, does not fit the standard definitions for intravenous solutions used in clinical settings and is not classified as an administered solution like the others listed. Thus, 0.9% Normal Saline stands out as the only option among the choices provided that consistently maintains isotonicity in clinical application.