Example of isotonic fluid?

Appeared in: AIIMS Delhi NO - 2017

Explanation

Isotonic fluids have a solute concentration (tonicity) similar to that of blood plasma, preventing major fluid shifts between compartments.
Ringer's Lactate (RL) is a classic example of an isotonic solution, with an osmolarity of approximately 274 mOsm/L.
It is a balanced electrolyte solution used for volume expansion and to correct dehydration.
Because its tonicity matches the body's, it increases extracellular fluid volume without causing cells to shrink or swell.

Option A: 45% NS (Normal Saline) is a hypotonic solution, not isotonic. Its solute concentration is lower than that of blood plasma.
Option C: Mannitol is a hypertonic solution, specifically an osmotic diuretic. Its concentration is much higher than that of blood plasma.
Option D: This option is incorrect because the choices represent three different types of fluid tonicity (hypotonic, isotonic, and hypertonic).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of Intravenous Fluids as background academic context rather than a clinical decision trigger.
Isotonic solutions like Ringer's Lactate and 0.9% Normal Saline are the cornerstone of fluid resuscitation for patients with hypovolemia (low blood volume) from hemorrhage, severe vomiting, or diarrhea.
Nurses must monitor patients receiving any IV fluid for signs of fluid volume excess (hypervolemia), such as crackles in the lungs, edema, and shortness of breath, especially in patients with heart failure or kidney disease.
What if? If a patient had severe hyponatremia (low sodium) with cerebral edema, a hypertonic solution like 3% NaCl would be used instead of an isotonic one to pull fluid from the brain cells and reduce swelling.

How to Approach the Question

First, identify the core concept of the question, which is 'isotonic fluid'.
Recall the definition of an isotonic solution: a fluid with a solute concentration similar to blood plasma.
Mentally classify each option based on its tonicity.
Option A, 0.45% NS, is half-normal saline, which is hypotonic.
Option B, RL (Ringer's Lactate), is a known isotonic solution.
Option C, Mannitol, is an osmotic diuretic, which is hypertonic.

Concept Tested & Keywords

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

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

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