Which of the following is hypotonic solution?

RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

Pharmacology

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

Explanation

45% saline, also known as half-strength normal saline, has a lower solute concentration (osmolarity of 154 mOsm/L) than human plasma (290 mOsm/L).
When administered, this lower concentration causes a net movement of water from the bloodstream into the interstitial fluid and cells, leading to cellular hydration.
It is classified as a hypotonic crystalloid solution and is primarily used to treat cellular dehydration and hypernatremia (high sodium levels).

Option B: 5% dextrose in water (D5W) is considered isotonic in the IV bag (~252 mOsm/L). Although it exerts a hypotonic effect in the body after the dextrose is rapidly metabolized, 0.45% saline is a true hypotonic solution from the start.
Option C: 10% dextrose in water (D10W) is a hypertonic solution (~505 mOsm/L). Its high concentration of dextrose pulls fluid from the cells into the vascular space.
Option D: 5% dextrose in 0.9% saline (D5NS) is a hypertonic solution (~560 mOsm/L). It combines an isotonic solution (0.9% saline) with 5% dextrose, resulting in a significantly higher osmolarity than plasma.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Tonicity of Intravenous (IV) Fluids as background academic context rather than a clinical decision trigger.
Administering hypotonic solutions requires careful nursing assessment for signs of fluid shifts, particularly cerebral edema (headache, confusion, decreased level of consciousness), as fluid moves into brain cells.
Hypotonic fluids are generally contraindicated in patients at risk for increased intracranial pressure (e.g., head trauma), those with extensive burns, or patients with liver disease, as it can worsen third-spacing and edema.
What if the patient was in hypovolemic shock? An isotonic solution (like 0.9% Saline or Lactated Ringer's) would be the fluid of choice, not a hypotonic solution. Isotonic fluids expand the intravascular volume without causing major fluid shifts into the cells, which is critical for restoring blood pressure.

How to Approach the Question

First, identify the key concept in the question stem, which is 'hypotonic solution'.
Recall the definitions of tonicity: hypotonic (lower solute concentration than cells), isotonic (same concentration), and hypertonic (higher concentration).
Analyze each option based on its composition. Remember that 'normal saline' is 0.9% NaCl and is isotonic. Therefore, 0.45% saline is 'half-normal' and must be hypotonic.
Evaluate the dextrose solutions. D5W is a special case (isotonic in bag, hypotonic in body). Higher concentrations of dextrose (>5%) are hypertonic.
Consider combined solutions like D5NS. Adding dextrose to an isotonic solution makes the final product hypertonic.
Compare the options and select the one that is most clearly and directly classified as hypotonic, which is 0.45% saline.

Concept Tested & Keywords

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