Identify the isotonic fluid among the following?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Medical & Surgical Nursing

Medium

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Explanation

Isotonic fluids have an osmolality close to that of the body's own plasma (275-295 mOsm/L), meaning they do not cause significant fluid shifts between the intracellular and extracellular compartments.
Both 0.9% Normal Saline (NS) and Lactated Ringer's (RL) are standard isotonic solutions used to expand the extracellular fluid volume, making them suitable for treating conditions like hypovolemia.
5% Dextrose in Water (D5W) is also classified as an isotonic solution based on its tonicity in the IV bag (~272 mOsm/L).
However, D5W becomes physiologically hypotonic once infused because the dextrose is quickly metabolized by the body, leaving behind free water.
Since all three fluids are classified as isotonic based on their initial composition, and an 'all the above' option is available, it is the most comprehensive and correct answer.

Option A: This is an incomplete answer. While 0.9% NS is a correct example of an isotonic fluid, it is not the only one listed. The question has an 'all the above' option which must be considered.
Option B: This is an incomplete answer. While 5% Dextrose is classified as isotonic based on its initial tonicity, it is not the only correct option provided.
Option C: This is an incomplete answer. While Ringer's Lactate (RL) is a correct example of an isotonic fluid, other options are also correct, making 'all the above' the best choice.

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.
Understanding IV fluid tonicity is crucial for safe nursing practice. Administering the wrong fluid type can lead to serious complications like cellular dehydration or cerebral edema.
Nurses must recognize that D5W, despite being isotonic in the bag, does not expand the intravascular volume and is not used for fluid resuscitation in hypovolemic shock. It primarily provides free water and calories.
What if? If a patient has increased intracranial pressure (ICP), D5W would be strictly contraindicated. Its physiologically hypotonic effect would cause fluid to shift into the brain cells, worsening cerebral edema and increasing ICP further.

How to Approach the Question

First, identify the core concept of the question, which is 'isotonic fluid'.
Define 'isotonic' in the context of IV therapy: a solution with a solute concentration similar to blood plasma.
Systematically evaluate each option against this definition.
Recall that 0.9% NS and RL are standard isotonic solutions.
Remember the special characteristic of 5% Dextrose (D5W): it is classified as isotonic but acts as a hypotonic solution in the body.
Observe that an 'all the above' option is present. Since options A, B, and C all fall under the classification of isotonic fluids (based on their initial tonicity), this becomes the most complete and correct answer.

Concept Tested & Keywords

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