0.45% NS is?

AIIMS Delhi NO- 2019

Pharmacology

Medium

Appeared in: AIIMS Delhi NO- 2019

Explanation

45% Normal Saline (NS), also known as half-normal saline, is classified as a hypotonic solution.
It has an osmolarity of approximately 154 mOsm/L, which is lower than the normal osmolarity of blood plasma (around 275-295 mOsm/L).
When administered, it causes fluid to shift from the intravascular space into the intracellular and interstitial spaces, leading to cellular hydration.
It is used to treat conditions like hypertonic dehydration and to provide free water to aid kidney function.

Option B: An isotonic solution has an osmolarity similar to that of blood plasma. The standard isotonic saline solution is 0.9% NS.
Option C: A hypertonic solution has a higher osmolarity than blood plasma, causing fluid to move out of cells. Examples include 3% or 5% NS.
Option D: Colloids are solutions containing large molecules (like proteins or starches) that do not easily cross cell membranes and primarily stay in the intravascular space to expand plasma volume. 0.45% NS is a crystalloid, containing small, diffusible salt molecules.

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.
Nurses must select the correct IV fluid based on the patient's condition (e.g., dehydration, fluid overload, electrolyte imbalance) as incorrect administration can lead to serious complications like cerebral edema or fluid volume overload.
When administering hypotonic solutions like 0.45% NS, it is crucial to monitor the patient's neurological status for signs of cerebral edema (e.g., confusion, headache, lethargy), especially in patients at risk for increased intracranial pressure.
What if? If a patient presented with severe hyponatremia and neurological symptoms (like seizures), a hypertonic solution (e.g., 3% NS) would be indicated to rapidly increase serum sodium and pull fluid out of swollen brain cells. Administering 0.45% NS would be contraindicated and dangerous in this scenario.

How to Approach the Question

Identify the core of the question: It asks for the classification of a specific IV fluid, 0.45% NS.
Recall the definitions of tonicity: hypotonic, isotonic, and hypertonic, relative to the body's plasma.
Remember that 0.9% NS is the baseline for 'normal' or isotonic saline.
Reason that since 0.45% is half the concentration of 0.9%, it must have a lower solute concentration (osmolarity) than plasma.
Conclude that a solution with a lower concentration than plasma is, by definition, hypotonic.
Evaluate the options based on this deduction and differentiate from colloids, which are classified by particle size, not just tonicity.

Concept Tested & Keywords

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