Isotonic solution

Appeared in: KPSC Staff Nurse - 2015

Explanation

9% Sodium Chloride (Normal Saline) is an isotonic solution, meaning its concentration of solutes is similar to that of human blood plasma.
Its osmolarity is approximately 308 mOsm/L, which is close to the normal plasma osmolarity of 275-295 mOsm/L.
When administered, it primarily stays in the extracellular fluid (ECF) compartment, making it effective for increasing intravascular volume without causing major fluid shifts into or out of cells.
It is the only solution that can be administered with blood products.

Option B: 45% Sodium Chloride (Half-Normal Saline) is a hypotonic solution, with an osmolarity of about 154 mOsm/L. It has a lower solute concentration than plasma.
Option C: 10% Dextrose in water (D10W) is a hypertonic solution. Its osmolarity (around 505 mOsm/L) is significantly higher than that of plasma.
Option D: 25% Dextrose in water (D25W) is a highly hypertonic solution with a very high osmolarity (over 1200 mOsm/L).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Types of Intravenous (IV) Solutions and Tonicity as background academic context rather than a clinical decision trigger.
Administering the correct type of IV fluid is a critical nursing responsibility to ensure patient safety and prevent complications.
Using a hypotonic solution in a patient with increased intracranial pressure (ICP) can worsen cerebral edema and lead to brain herniation.
Administering isotonic fluids requires monitoring for signs of fluid volume excess (hypervolemia), such as crackles in the lungs, edema, and hypertension, especially in patients with heart failure or kidney disease.

How to Approach the Question

First, understand the question's core concept, which is identifying an 'isotonic solution'.
Define 'isotonic' in a clinical context: a solution with a solute concentration similar to blood plasma (osmolarity of roughly 275-295 mOsm/L).
Recall or deduce the tonicity of the common IV fluids listed in the options.
Evaluate each option: 0.9% NaCl is the standard isotonic solution. 0.45% NaCl is half the concentration, making it hypotonic. Dextrose solutions above 5% are hypertonic.
Select the option that matches the definition of an isotonic solution.

Concept Tested & Keywords

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

Practise the full KPSC Staff Nurse - 2015

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