Which among the following solutions is hypotonic?

Appeared in: AIIMS Delhi NO-2016

Explanation

45% NS (half-normal saline) is a hypotonic solution because it has a lower solute concentration (osmolality of 154 mOsm/L) compared to blood plasma (285 mOsm/L).
This lower concentration creates an osmotic gradient that causes water to move from the bloodstream into the cells.
This action helps to rehydrate cells and is used to treat conditions like hypernatremia (high sodium) and cellular dehydration.

Option B: 9% NS (Normal Saline) is an isotonic solution, meaning it has the same solute concentration as blood plasma. It does not cause a significant fluid shift into or out of cells.
Option C: 3% NS is a hypertonic solution. It has a much higher solute concentration than blood, which pulls water out of cells, causing them to shrink.
Option D: 5% Dextrose in Water (D5W) is isotonic in the IV bag but becomes physiologically hypotonic after the body metabolizes the dextrose. While it has a hypotonic effect, 0.45% NS is a true hypotonic solution by its composition and the most direct answer.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Tonicity of Intravenous (IV) Solutions as background academic context rather than a clinical decision trigger.
Administering the correct type of IV fluid is critical for patient safety. Using the wrong solution can lead to serious complications.
Administering a hypotonic solution to a patient at risk for increased intracranial pressure (e.g., head injury) is contraindicated because it can worsen cerebral edema by shifting fluid into brain cells.
Nurses must carefully monitor patients receiving hypotonic fluids for signs of fluid shifts, such as changes in level of consciousness, which could indicate cerebral edema, or worsening hypotension.

How to Approach the Question

First, identify the key term in the question: 'hypotonic'.
Recall the definition of a hypotonic solution: a solution with a lower solute concentration than body fluids, which causes water to move into cells.
Mentally review the common classifications of IV fluids: hypotonic, isotonic, and hypertonic.
Evaluate each option: 0.45% NS is half the strength of isotonic saline, making it hypotonic. 0.9% NS is the standard for isotonic. 3% NS is a high concentration, making it hypertonic. D5W is isotonic in the bag but has a hypotonic effect.
Compare the options. 0.45% NS is the most direct and classic example of a hypotonic solution.
Select the option that best fits the definition of a hypotonic solution.

Concept Tested & Keywords

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E6 Nursing Fundamentals Potter Perry 12e Part 5 p. 68-70

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Attempt every question from this paper in a timed mock, then review the full solution for each one.