What are hypotonic salt solution

Isotonic, hypotonic, and hypertonic solutions are widely used in the healthcare setting and as a nurse you must know how each of the solutions work on the body and why they are given.

In nursing school and on the NCLEX exam, you will be required to know what type of IV fluids are considered isotonic, hypotonic, and hypertonic. In this article, I give you an easy overview of each solution and how they work on the cellular level.

In addition, I have an isotonic, hypotonic, and hypertonic quiz you can take to test your knowledge on this content.

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Isotonic, Hypotonic, & Hypertonic Fluids for Nursing Students

First, let’s get familiar with the cell and how tonicity works through osmosis.

The cell is divided into two parts: (intracellular & extracellular). Each part is made up of a solution and depending on the tonicity of the fluid you can having shifting of fluids from outside of the cell to the inside via osmosis.

The cell loves to be in an isotonic state and when something happens to make it unequal (like with hypotonic or hypertonic conditions) it will use osmosis to try to equal it out.

Osmosis allows molecules of the solvent to pass through a semipermeable membrane from a less concentrated solution to a higher concentrated solution. The key thing to remember here is that everything will move from a LOW concentration to a HIGH concentration.

Remember when we are talking about isotonic and hypo/hypertonic we are talking about how it looks outside of the cell compared to inside.

Easy Overview of Isotonic, Hypotonic, & Hypertonic Solutions


Iso: same/equal

Tonic: concentration of a solution

The cell has the same concentration on the inside and outside which in normal conditions the cell’s intracellular and extracellular are both isotonic.

It is important to be familiar with what fluids are isotonic and when they are given.

Isotonic fluids

  • 0.9% Saline
  • 5% dextrose in water (D5W)**also used as a hypotonic solution after it is administered because the body absorbs the dextrose BUT it is considered isotonic)
  • 5% Dextrose in 0.225% saline (D5W1/4NS)
  • Lactated Ringer’s

Isotonic solutions are used: to increase the EXTRACELLULAR fluid volume due to blood loss, surgery, dehydration, fluid loss that has been loss extracellularly.


Hypo: ”under/beneath”

Tonic: concentration of a solution

The cell has a low amount of solute extracellularly and it wants to shift inside the cell to get everything back to normal via osmosis. This will cause CELL SWELLING which can cause the cell to burst or lyses.

Hypotonic solutions

  • 0.45% Saline (1/2 NS)
  • 0.225% Saline (1/4 NS)
  • 0.33% saline (1/3 NS)

Hypotonic solutions are used when the cell is dehydrated and fluids need to be put back intracellularly. This happens when patients develop diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemia.

Important: Watch out for depleting the circulatory system of fluid since you are trying to push extracellular fluid into the cell to re-hydrate it. Never give hypotonic solutions to patient who are at risk for increased cranial pressure (can cause fluid to shift to brain tissue), extensive burns, trauma (already hypovolemic) etc. because you can deplete their fluid volume.


Hyper: excessive

Tonic: concentration of a solution

The cell has an excessive amount of solute extracellularly and osmosis is causing water to rush out of the cell intracellularly to the extracellular area which will cause the CELL TO SHRINK.

Hypertonic solutions

  • 3% Saline
  • 5% Saline
  • 10% Dextrose in Water (D10W)
  • 5% Dextrose in 0.9% Saline
  • 5% Dextrose in 0.45% saline
  • 5% Dextrose in Lactated Ringer’s

When hypertonic solutions are used (very cautiously….most likely to be given in the ICU due to quickly arising side effects of pulmonary edema/fluid over load). In addition, it is prefered to give hypertonic solutions via a central line due to the hypertonic solution being vesicant on the veins and the risk of infiltration.

Take the Isotonic, Hypotonic & Hypertonic Solution Quiz