Which of the following is not an isotonic fluid?

Appeared in: Chitranjjan National Cancer Institute Kolkata - 2021

Explanation

Dextrose 5% in normal saline (D5NS) is classified as a hypertonic solution.
It is a combination of two substances: 5% dextrose and 0.9% sodium chloride (Normal Saline).
This combination results in a high solute concentration (osmolality) that is greater than that of blood plasma.
When infused, its hypertonicity causes water to shift from the intracellular and interstitial spaces into the intravascular space.

Option A: 9% Sodium Chloride, also known as Normal Saline (NS), is the standard isotonic solution. Its osmolality is very close to that of blood plasma.
Option B: Ringer's Lactate (RL) is another common isotonic solution. It contains multiple electrolytes in concentrations similar to plasma.
Option C: Dextrose 5% in water (D5W) is considered isotonic in the IV bag. Although it becomes physiologically hypotonic once the dextrose is metabolized, it is not hypertonic.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of intravenous (IV) fluids based on tonicity as background academic context rather than a clinical decision trigger.
Administering hypertonic solutions like D5NS requires vigilant nursing assessment for signs of fluid volume overload, such as crackles in the lungs, shortness of breath, jugular vein distention, and peripheral edema.
Patients receiving hypertonic fluids must be monitored for hypernatremia and changes in neurological status, as rapid fluid shifts can be dangerous.
What if? If a patient had critical, symptomatic hyponatremia (low sodium), a more potent hypertonic solution like 3% Saline might be ordered to rapidly pull water out of swollen brain cells. This is a high-risk intervention requiring intensive care monitoring, and D5NS would not be sufficient.

How to Approach the Question

First, identify the negative keyword 'NOT'. This tells you to look for the one option that is different from the others, specifically the one that is not isotonic.
Second, recall the definitions of the three main types of IV fluids: isotonic (same concentration as blood), hypotonic (lower concentration), and hypertonic (higher concentration).
Third, analyze each option based on its composition. 0.9% (Normal Saline) and RL (Ringer's Lactate) are classic isotonic solutions.
Fourth, consider the special cases. D5W is isotonic in the bag but becomes hypotonic in the body. D5NS is a combination of an isotonic solution (NS) and dextrose, which makes the final product hypertonic.
Fifth, based on the analysis, Dextrose 5% in normal saline is the only hypertonic solution among the choices.
Finally, select this option as it is the one that is 'NOT' isotonic.

Concept Tested & Keywords

Concept Tested: Classification of intravenous (IV) fluids based on tonicity.
Stem keywords: isotonic fluid
Lead-in keywords: not
Negative lead-in flag: The question asks to identify the option that is an exception, meaning it is NOT an isotonic fluid.

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

E6 Nursing Brunner Adult Health 3SA Vol 1 Part 1 p. 142-144

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