Fluid & Electrolyte Q 102

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Mr. Wenceslao is scheduled to receive an isotonic solution; which one of the following is an example of such a solution?

  

    A. D10% W

    B. 0.45% saline

    C. 0.9% saline

    D. 3% normal saline W

    

    

Correct Answer: C. A solution of 0.9% saline is isotonic.

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A solution of 0.9% saline is isotonic. Solutions of 0.33% and 0.45% saline and D5W are hypotonic. An isotonic solution is one that has the same osmolarity, or solute concentration, as another solution. If these two solutions are separated by a semipermeable membrane, water will flow in equal parts out of each solution and into the other.

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Option A: D10% W is a crystalloid fluid. Crystalloid fluids are a subset of intravenous solutions that are frequently used in the clinical setting. Crystalloid fluids are the first choice for fluid resuscitation in the presence of hypovolemia, hemorrhage, sepsis, and dehydration.

Option B: 0.45% saline is a hypotonic solution. If a cell is placed in a hypotonic solution, there will be a net flow of water into the cell, and the cell will gain volume. If the solute concentration outside the cell is lower than inside the cell, and the solutes cannot cross the membrane, then that solution is hypotonic to the cell.

Option D: 0.33% saline is a hypotonic solution. In the case of a plant cell, however, a hypotonic extracellular solution is actually ideal. The plasma membrane can only expand to the limit of the rigid cell wall, so the cell won’t burst, or lyse.

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