0.45% normal saline is a?

AIIMS Rishikesh & Jodhpur NO - 2017

Pharmacology

Medium

Appeared in: AIIMS Rishikesh & Jodhpur NO - 2017

Explanation

45% Normal Saline (NS) is classified as a hypotonic solution because its solute concentration (osmolality of 154 mOsm/L) is lower than that of human blood plasma (275-295 mOsm/L).
Due to the principles of osmosis, when a hypotonic solution is infused, water moves from the area of lower solute concentration (the bloodstream) to the area of higher solute concentration (inside the body's cells).
This fluid shift rehydrates the cells, making it useful for treating conditions of cellular dehydration, such as hypernatremia or as a maintenance fluid.
It is also known as 'half-strength normal saline' because its sodium chloride concentration is half that of 'normal' (isotonic) saline (0.9% NS).

Option B: Isotonic solutions have the same osmolality as body fluids. The standard isotonic saline solution is 0.9% NaCl, not 0.45%.
Option C: Hypertonic solutions have a higher osmolality than body fluids. 0.45% NS has a lower osmolality.
Option D: Colloids are solutions containing large molecules (like proteins) that do not readily pass through capillary membranes and are used as plasma volume expanders. 0.45% NS is a crystalloid solution, containing small molecules that can easily move between fluid compartments.

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.
When administering hypotonic fluids like 0.45% NS, nurses must vigilantly monitor for signs of a fluid shift from the vascular space into the cells. This includes assessing for hypotension (due to decreased blood volume) and changes in neurological status (which could indicate cerebral edema).
Hypotonic solutions are contraindicated in patients at risk for increased intracranial pressure (e.g., head injury, stroke), as the fluid shift into brain cells can worsen cerebral edema and lead to severe complications.
What if? If a patient has severe hyponatremia (low sodium) with neurological symptoms, the correct fluid would be a hypertonic solution (like 3% Saline), not a hypotonic one. Giving 0.45% NS would worsen the hyponatremia and increase the risk of seizures and brain swelling.

How to Approach the Question

First, identify the core of the question, which is to classify the tonicity of '0.45% normal saline'.
Recall the standard benchmark for intravenous saline solutions: 0.9% Normal Saline is defined as an 'isotonic' solution, meaning it has a similar solute concentration to human blood.
Compare the given concentration (0.45%) to the isotonic benchmark (0.9%). Since 0.45% is exactly half the concentration of isotonic saline, it must have a lower solute concentration.
Apply the definitions of tonicity: a solution with a lower concentration is 'hypotonic', the same concentration is 'isotonic', and a higher concentration is 'hypertonic'.
Based on this comparison, conclude that 0.45% normal saline is a hypotonic solution.
Eliminate 'Colloid' as it refers to a different type of solution based on molecule size (large proteins), whereas saline is a crystalloid (small molecules).

Concept Tested & Keywords

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